The DOI matches its Crossref record; 27 of the 28 references it cites were found in a registry or an index, and 1 are not checked yet; 2 of the 18 sources its claims cite were checked for support.
Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant
Open accessPublished version of a preprint
Abstract
Abstract Background The B.1.617.2 COVID-19 variant has contributed to the surge in cases in India and has now been detected across the globe, including a notable increase in cases in the UK. We estimate the effectiveness of the BNT162b2 and ChAdOx1 COVID-19 vaccines against this variant. Methods A test negative case control design was used to estimate the effectiveness of vaccination against symptomatic disease with both variants over the period that B.1.617.2 began circulating with cases identified based on sequencing and S-gene target status. Data on all symptomatic sequenced cases of COVID-19 in England was used to estimate the proportion of cases with B.1.617.2 compared to the predominant strain (B.1.1.7) by vaccination status. Results Effectiveness was notably lower after 1 dose of vaccine with B.1.617.2 cases 33.5% (95%CI: 20.6 to 44.3) compared to B.1.1.7 cases 51.1% (95%CI: 47.3 to 54.7) with similar results for both vaccines. With BNT162b2 2 dose effectiveness reduced from 93.4% (95%CI: 90.4 to 95.5) with B.1.1.7 to 87.9% (95%CI: 78.2 to 93.2) with B.1.617.2. With ChAdOx1 2 dose effectiveness reduced from 66.1% (95% CI: 54.0 to 75.0) with B.1.1.7 to 59.8% (95%CI: 28.9 to 77.3) with B.1.617.2. Sequenced cases detected after 1 or 2 doses of vaccination had a higher odds of infection with B.1.617.2 compared to unvaccinated cases (OR 1.40; 95%CI: 1.13-1.75). Conclusions After 2 doses of either vaccine there were only modest differences in vaccine effectiveness with the B.1.617.2 variant. Absolute differences in vaccine effectiveness were more marked with dose 1. This would support maximising vaccine uptake with two doses among vulnerable groups.
Verified 2026-10-06 · 1 reference not checked yet
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16 Own result · 11 Not checked yet · 9 Own method · 1 Supported · 1 Partly supported · 1 No basis given · accuracy not yet measured
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In the paper
“Several of these mutations may affect immune responses directed toward the key antigenic regions of receptor-binding protein (452 and 478) and deletion of part of the N-terminal domain.23”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Abstract > Conclusions
What the sources say
- Partly supportedcites [23] Li Q, Wu J, Nie J, et al. The impact of mutations in SARS-CoV-2 spike on viral infectivity and antigenicity. Cell 2020; 182(5): 1284.e9- 1294.e9. 32730807 PMC7366990 sourceExperimental — accuracy not yet measured
The Discussion reports that L452R reduced sensitivity to neutralizing antibodies, and Table 1 lists reduced sensitivity to convalescent sera for T478I and Y145del. But this 2020 paper does not assess the delta variant or its specific mutation at position 478 and N-terminal-domain deletion, so it supports the possibility of immune effects at those regions rather than the claim about delta’s mutations specifically. (LLM, conf=0.87)
hedgedconditional- Asserted: passes — The authors put it forward as true.
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- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
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- Partly supported
Every source the paper cites for this claim was checked and supports it.
In the paper
“As compared with recent findings from Qatar on the effectiveness of the BNT162b2 vaccine against the alpha and beta variants,17 our findings suggest that effectiveness against the delta variant after a full vaccination course lies somewhere between these two.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
What the sources say
- Supportedcites [17] Abu-Raddad LJ, Chemaitelly H, Butt AA. Effectiveness of the BNT162b2 Covid-19 vaccine against the B.1.1.7 and B.1.351 variants. N Engl J Med 2021; 385: 187- 189. 33951357 PMC8117967 source
The cited paper reports Qatar estimates for BNT162b2 effectiveness against documented alpha (B.1.1.7) and beta (B.1.351) infections at 14 or more days after the second dose: 89.5% and 75.0%, respectively (main text and Table 1; page not provided). The citing authors’ comparison with their own delta finding is their conclusion, not a finding attributed to this source. (LLM, conf=0.94)
hedged- Asserted: passes — The authors put it forward as true.
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- Supported
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“the results were similar for both vaccines.”
- Also stated in: § Vaccine Effectiveness Estimates · plain
“Results for the first dose were similar for both vaccines, with an absolute difference in vaccine effectiveness against the delta variant as compared with the alpha variant of 11.9 percentage points with the BNT162b2 vaccine and 18.7 percentage points with the ChAdOx1 nCoV-19 vaccine.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Abstract > Results
plain- Asserted: passes — The authors put it forward as true.
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- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
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- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Vaccine Effectiveness Estimates · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Effectiveness after one dose of vaccine (BNT162b2 or ChAdOx1 nCoV-19) was notably lower among persons with the delta variant (30.7%; 95% confidence interval [CI], 25.2 to 35.7) than among those with the alpha variant (48.7%; 95% CI, 45.5 to 51.7); the results were similar for both vaccines.”
- Also stated in: § Vaccine Effectiveness Estimates · plain
“In the “any vaccine” analysis, in which data from the persons who received either vaccine were pooled, effectiveness was notably lower after the first vaccine dose among persons with the delta variant (30.7%; 95% confidence interval [CI], 25.2 to 35.7) than among those with the alpha variant (48.7%; 95% CI, 45.5 to 51.7).”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Abstract > Results
plaincorrelational- Asserted: passes — The authors put it forward as true.
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- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Vaccine Effectiveness Estimates · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“With the ChAdOx1 nCoV-19 vaccine, the effectiveness of two doses was 74.5% (95% CI, 68.4 to 79.4) among persons with the alpha variant and 67.0% (95% CI, 61.3 to 71.8) among those with the delta variant.”
- Also stated in: § Vaccine Effectiveness Estimates · plain
“The effectiveness with two doses of the ChAdOx1 nCoV-19 vaccine was lower than with the BNT162b2 vaccine; however, with the ChAdOx1 nCoV-19 vaccine, the difference in effectiveness between the alpha and delta variants was small (74.5% [95% CI, 68.4 to 79.4] and 67.0% [95% CI, 61.3 to 71.8], respectively).”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Abstract > Results
plaindirect- Asserted: passes — The authors put it forward as true.
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- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Vaccine Effectiveness Estimates · plain
None of the sources cited for this claim have been checked yet.
In the paper
“The effectiveness with two doses of the ChAdOx1 nCoV-19 vaccine was lower than with the BNT162b2 vaccine; however, with the ChAdOx1 nCoV-19 vaccine, the difference in effectiveness between the alpha and delta variants was small (74.5% [95% CI, 68.4 to 79.4] and 67.0% [95% CI, 61.3 to 71.8], respectively).”
- Also stated in: § Discussion · plain
“Vaccine effectiveness against either variant was smaller after the receipt of two doses of the ChAdOx1 nCoV-19 vaccine than after the receipt of two doses of the BNT162b2 vaccine, a finding that is consistent with reported clinical trial findings.7,8”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Vaccine Effectiveness Estimates
What the sources say
- Not checked yetcites [7] Polack FP, Thomas SJ, Kitchin N, et al. Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine. N Engl J Med 2020; 383: 2603- 2615. 33301246 PMC7745181 source
- Not checked yetcites [8] Voysey M, Clemens SAC, Madhi SA, et al. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK. Lancet 2021; 397: 99- 111. 33306989 PMC7723445 source
plaindirect- Asserted: passes — The authors put it forward as true.
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- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Discussion · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Among all the sequenced samples that were linked to the SARS-CoV-2 testing data set, 92.9% were linked to data on vaccination status.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Data Linkage
plaincorrelational- Asserted: passes — The authors put it forward as true.
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A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“These estimates were only modestly lower than the estimate of vaccine effectiveness against the alpha variant.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
plain- Asserted: passes — The authors put it forward as true.
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- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“The numbers of cases and follow-up periods are currently insufficient for the estimation of vaccine effectiveness against severe disease, including hospitalization and death.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“The alpha variant accounts for between 98% and 100% of S target–negative results in England.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Methods > Data Sources
plaincorrelational- Asserted: passes — The authors put it forward as true.
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- It may state two separate claims as one. 17
- The quote only partly states this claim. 2
- Probably not a substantial claim. 8
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“With the BNT162b2 vaccine, the effectiveness of two doses was 93.7% (95% CI, 91.6 to 95.3) among persons with the alpha variant and 88.0% (95% CI, 85.3 to 90.1) among those with the delta variant.”
- Also stated in: § Vaccine Effectiveness Estimates · plain
“With the BNT162b2 vaccine, a small difference in effectiveness between variants was seen after the second dose: 93.7% (95% CI, 91.6 to 95.3) with the alpha variant and 88.0% (95% CI, 85.3 to 90.1) with the delta variant.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Abstract > Results
plaindirect- Asserted: passes — The authors put it forward as true.
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It may state two separate claims as one.
- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Vaccine Effectiveness Estimates · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Results for the first dose were similar for both vaccines, with an absolute difference in vaccine effectiveness against the delta variant as compared with the alpha variant of 11.9 percentage points with the BNT162b2 vaccine and 18.7 percentage points with the ChAdOx1 nCoV-19 vaccine.”
- Also stated in: § Discussion · plain
“We found that the absolute difference in vaccine effectiveness against symptomatic disease with one dose of vaccine with the delta variant as compared with the alpha variant was approximately 12 to 19 percentage points.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Vaccine Effectiveness Estimates
plain- Asserted: passes — The authors put it forward as true.
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It may state two separate claims as one.
- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Discussion · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Overall, we found high levels of vaccine effectiveness against symptomatic disease with the delta variant after the receipt of two doses.”
- Also stated in: § Discussion · boosted
“A clear effect was noted with both vaccines, with high levels of effectiveness after two doses.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
boosteddirect- Asserted: passes — The authors put it forward as true.
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It may state two separate claims as one.
- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Discussion · boosted
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“In the “any vaccine” analysis, the vaccine effectiveness was 87.5% (95% CI, 85.1 to 89.5) with the alpha variant and 79.6% (95% CI, 76.7 to 82.1) with the delta variant.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Vaccine Effectiveness Estimates
plaindirect- Asserted: passes — The authors put it forward as true.
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It may state two separate claims as one. The quote only partly states this claim.
- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“In an analysis that was restricted to including only persons at least 16 years of age who had symptomatic Covid-19 caused by the alpha or delta variant and who had been vaccinated with either ChAdOx1 nCoV-19 or BNT162b2 according to an appropriate schedule, 19,109 sequenced cases were included (Fig. S1 in the Supplementary Appendix). The alpha variant was detected in 14,837 samples, and the delta”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Data Linkage
plainn = 19,109- Asserted: passes — The authors put it forward as true.
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A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Among sequenced samples that were originally tested with the use of the TaqPath assay, a high correlation was seen between S target status and the two variants under investigation, with 95.3% of the S target–positive cases identified as having the delta variant and 99.6% of the S target–negative cases identified as having the alpha variant (Tables S1 and S2).”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Descriptive Characteristics
plaincorrelational- Asserted: passes — The authors put it forward as true.
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A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Table S3, in which the period after the first dose is stratified according to the period of 21 to 55 days and the period of 56 or more days, shows a possible indication of waning efficacy against the alpha variant with the BNT162b2 vaccine and against the delta variant with the ChAdOx1 nCoV-19 vaccine.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Vaccine Effectiveness Estimates
hedgedconditional- Asserted: passes — The authors put it forward as true.
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A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Few cases of either variant were seen in persons older than 70 years of age, and only nine cases (all of which were with the alpha variant) occurred among care home residents.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Descriptive Characteristics
plainn = 9- Asserted: passes — The authors put it forward as true.
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Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Only modest differences in vaccine effectiveness were noted with the delta variant as compared with the alpha variant after the receipt of two vaccine doses.”
- Also stated in: § Vaccine Effectiveness Estimates · plain
“The difference in vaccine effectiveness was much smaller among persons who had received the second dose of vaccine.”
- Also stated in: § Discussion · plain
“However, the differences in vaccine effectiveness after two doses were small.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Abstract > Conclusions
plain- Asserted: passes — The authors put it forward as true.
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- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
- Also stated in: § Vaccine Effectiveness Estimates · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Key differences with the delta variant included a higher proportion of persons with a history of foreign travel; a higher proportion of persons with cases in the most recent weeks (calendar weeks 18 to 20); a higher proportion of persons with cases in the northwest region, London, and the east of England; and a higher proportion of persons in the “Indian or British Indian,” “Pakistani or British”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Results > Descriptive Characteristics
plaincorrelational- Asserted: passes — The authors put it forward as true.
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A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“In the test-negative case–control analysis, the estimated vaccine effectiveness against symptomatic disease with the delta variant was approximately 36% with a single dose of the BNT162b2 vaccine and approximately 30% with a single dose of the ChAdOx1 nCoV-19 vaccine; the effectiveness was approximately 88% with two doses of the BNT162b2 vaccine and approximately 67% with two doses of the ChAdOx1”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
hedgeddirect- Asserted: passes — The authors put it forward as true.
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It may state two separate claims as one.
- The authors state this as an assumption: The accuracy of sequencing would not depend on the variant.
- The authors state this as an assumption: The propensity among symptomatic persons to get tested would not differ according to variant.
In the paper
“P681R is at the S1–S2 cleavage site, and it appears that strains with mutations at that site may have increased replication, which leads to higher viral loads and increased transmission.24”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Abstract > Conclusions
What the sources say
- Not checked yetcites [24] Johnson BA, Xie X, Kalveram B, et al. Furin cleavage site is key to SARS-CoV-2 pathogenesis. August 26, 2020 (https://www.biorxiv.org/content/10.1101/2020.08.26.268854v1). preprint.
hedgedconditional- Asserted: passes — The authors put it forward as true.
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Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“The use of a test-negative case–control design helped us to control for differences in health-seeking behavior between vaccinated persons and unvaccinated persons.”
- Also stated in: § Study Design · plain
“This approach helps to control for biases related to health-seeking behavior, access to testing, and case ascertainment.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
plaindirect- Asserted: passes — The authors put it forward as true.
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In the paper
“Among sequenced samples that tested positive for the S target, the delta variant was in 72.2% of the samples in April 2021 and in 93.0% in May (as of May 12, 2021).4”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Methods > Data Sources
What the sources say
- Not checked yetcites [4] Public Health England. SARS-CoV-2 variants of concern and variants under investigation in England. Technical briefing 11. May 13, 2021 (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/986380/Variants_of_Concern_VOC_Technical_Briefing_11_England.pdf).
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“Assignment to the delta variant on the basis of S target status was restricted to the week commencing April 12, 2021, and onward in order to aim for high specificity of S target–positive testing for the delta variant.4”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Methods > Statistical Analysis
What the sources say
- Not checked yetcites [4] Public Health England. SARS-CoV-2 variants of concern and variants under investigation in England. Technical briefing 11. May 13, 2021 (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/986380/Variants_of_Concern_VOC_Technical_Briefing_11_England.pdf).
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“The proportion of all positive samples that were sequenced increased from approximately 10% in February 2021 to approximately 60% in May 2021.4”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Methods > Data Sources
What the sources say
- Not checked yetcites [4] Public Health England. SARS-CoV-2 variants of concern and variants under investigation in England. Technical briefing 11. May 13, 2021 (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/986380/Variants_of_Concern_VOC_Technical_Briefing_11_England.pdf).
plaindirect- Asserted: passes — The authors put it forward as true.
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In the paper
“Findings were also similar to those in cases that occurred during the first 2 weeks after receipt of the first vaccine dose (Table S4), which helps to rule out unmeasured confounders associated with both the likelihood of being vaccinated and the likelihood of being exposed to a variant.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“Comparison was made with unvaccinated persons and with persons who had symptom onset in the period of 4 to 13 days after vaccination in order to help account for differences in underlying risk of infection.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Methods > Statistical Analysis
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Low sensitivity or specificity of PCR testing could also affect one variant more than another, although this might be expected to affect the alpha variant more than the delta variant, given that, with an emerging variant, more cases may be detected earlier in infection, which may result in higher viral loads and increased sensitivity and specificity.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
hedgedconditional- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Although we controlled for race or ethnic group, region, and an index of multiple deprivation, differences in vaccine coverage among population groups that may have more or less exposure to the delta variant may have affected the secondary analysis but should not have affected the test-negative case–control design.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
hedgedconditional- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
It may state two separate claims as one.
In the paper
“There may also be differences among the populations that received each vaccine — for example, in younger age groups, health care workers are more likely to have received the BNT162b2 vaccine, whereas persons in clinical risk groups are more likely to have received the ChAdOx1 nCoV-19 vaccine.11”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
What the sources say
- Not checked yetcites [11] Hall VJ, Foulkes S, Saei A, et al. COVID-19 vaccine coverage in health-care workers in England and effectiveness of BNT162b2 mRNA vaccine against infection (SIREN): a prospective, multicentre, cohort study. Lancet 2021; 397: 1725- 1735. 33901423 PMC8064668 source
hedgedcorrelational- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Our study has several limitations. The findings are observational and should be interpreted with caution.”
§ Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant > Discussion
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it.
The authors state this as an assumption.
For the secondary analysis, if a vaccine had some efficacy and was equally effective against both variants, a similar proportion of cases with either variant would be expected in unvaccinated and vaccinated persons; if the vaccine was less effective against delta than alpha, delta would make up a higher proportion of cases occurring more than 3 weeks after vaccination than among unvaccinated.
“The underlying assumption was that if the vaccine had some efficacy and was equally effective against each variant, a similar proportion of cases with either variant would be expected in unvaccinated persons and in vaccinated persons. Conversely, if the vaccine was less effective against the delta variant than against the alpha variant, then the delta variant would be expected to make up a higher”
The authors state this as an assumption.
The accuracy of sequencing would not depend on the variant.
“that is, the accuracy of the sequencing would not depend on the variant”
The authors state this as an assumption.
The propensity among symptomatic persons to get tested would not differ according to variant.
“and the propensity among symptomatic persons to get tested would not differ according to variant.”
The paper relies on this without support.
The effectiveness of BNT162b2 and ChAdOx1 nCoV-19 against the delta variant was unclear or limited before this study.
“The effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against this variant has been unclear.”
“Data on the effectiveness of Covid-19 vaccines against clinical outcomes with this variant have been limited.”
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
The source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Modest reductions in vaccine effectiveness against infection and mild disease have been observed with the beta (B.1.351) and delta variants, although effectiveness against severe disease has remained high for at least 6 months after primary immunization with two Covid-19 vaccine doses.”
From Effectiveness of COVID-19 vaccines against the Omicron (B.1.1.529) variant of concern (2021) · cites this paper as [16]
Experimental — accuracy not yet measuredThe cited source says what the claim attributes to it.
In the citing paper
“Real-world setting studies performed, few months into vaccination campaigns, showed high effectiveness of these vaccines [1-8].”
In the citing paper
“In addition, there is evidence of modest reduction in vaccine effectiveness against infection with the delta variant.11”
From Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study (2022) · cites this paper as [11]
In the citing paper
“However, the cohort study design applied earlier to the same population of Qatar yielded findings similar to those of the test-negative case–control design36,38,39, supporting the validity of this standard approach in assessing vaccine effectiveness11,12,36,40.”
From Duration of mRNA vaccine protection against SARS-CoV-2 Omicron BA.1 and BA.2 subvariants in Qatar (2022) · cites this paper as [40]
In the citing paper
“Vaccine effectiveness against symptomatic SARS-CoV-2 Omicron (B.1.1.529)1 infection during the large Omicron wave in Qatar, between December 23, 2021 and February 28, 2022, was estimated using the test-negative, case–control study design, a standard design for assessing vaccine effectiveness11,12,36,40.”
From Duration of mRNA vaccine protection against SARS-CoV-2 Omicron BA.1 and BA.2 subvariants in Qatar (2022) · cites this paper as [40]
In the citing paper
“In case-control studies from the UK, the BNT162b vaccine was approximately 85% effective for the Delta variant whereas the AZD1222 vaccine was approximately 60% effective 232,233 .”
From The biological and clinical significance of emerging SARS-CoV-2 variants (2021) · cites this paper as [232]
In the citing paper
“With previous variants, vaccine effectiveness against severe disease, including hospitalization and death, has been higher and has been retained for a longer period than effectiveness against mild disease.”
From Effectiveness of COVID-19 vaccines against the Omicron (B.1.1.529) variant of concern (2021) · cites this paper as [16]
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Metadata
- Authors
- Lopez Bernal, J., Andrews, N., Gower, C., Gallagher, E., Simmons, R., Thelwall, S., Stowe, J., Tessier, E., Groves, N., Dabrera, G., Myers, R., Campbell, C. N. J., Amirthalingam, G., Edmunds, M., Zambon, M., Brown, K. E., Hopkins, S., Chand, M., & Ramsay, M.
- Affiliations
- From Public Health England (J.L.B., N.A., C.G., E.G., R.S., S.T., J.S., E.T., N.G., G.D., R.M., C.N.J.C., G.A., M.E., M.Z., K.E.B., S.H., M.C., M.R.), the National Institute of Health Research (NIHR) Health Protection Research Unit in Vaccines and Immunisation, London School of Hygiene and Tropical Medicine (J.L.B., N.A., C.N.J.C., G.A., K.E.B., M.R.), the NIHR Health Protection Research Unit in Respiratory Infections, Imperial College London (J.L.B., M.Z.), and Guy’s and St. Thomas’ Hospital NHS Trust (M.C.), London, and Healthcare Associated Infections and Antimicrobial Resistance, University of Oxford, Oxford (S.H.) — all in the United Kingdom.
- Public Health England (GB)
- ORCID
- Venue
- New England Journal of Medicine
- Publisher
- Massachusetts Medical Society
- Published
- 2021-08-12
- Volume
- 385
- Issue
- 7
- Pages
- 585-594
- ISSN
- 0028-4793 (ISSN-L)
- 1533-4406
- PMC
- PMC8314739
- OpenAlex
- W3184226105
- Cited by
- 2,889
- References
- 26
- Citations by year
- 2026: 37 · 2025: 82 · 2024: 184 · 2023: 431 · 2022: 1320 · 2021: 832
- FWCI
- 219.33
- Type
- journal article
- Language
- en
- Open access
- green
- doi.org
- Licence
- cc-by-nc-nd
- Locations
- New England Journal of Medicine (publishedVersion)
- medRxiv (acceptedVersion, cc-by-nc-nd)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Wellcome Trust
- Public Health England
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Social Sciences › Health › Vaccine Coverage and Hesitancy
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Keywords
- COVID-19 vaccines, B.1.1.7 Alpha variant, vaccine effectiveness, BNT162b2, ChAdOx1 nCoV-19 vaccine, two-dose vaccination, symptomatic COVID-19, test-negative case-control design
- MeSH terms
- Immunogenicity, Vaccine, COVID-19, SARS-CoV-2, COVID-19 Vaccines, Adolescent, Adult, Aged, Aged, 80 and over, Female, United Kingdom, Humans, Male, Middle Aged, Case-Control Studies, Treatment Outcome, Young Adult, Vaccine Potency
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
A language model drew the claims from the paper on 2026-10-06, under version 3 of the claim definition (model deepseek-v4.1-flash, prompt extract-v3).
A second model labelled each claim on 2026-10-06 (model jev-1.13-20260917, definition revision gold-guideline-v0.2).
Cited sources are checked with a language model’s help (gpt-6-sol).
Statistics and arithmetic are recomputed, not judged.
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