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Cited by 551SARS-CoV-2 and COVID-19 ResearchCOVID-19 epidemiological studiesCOVID-19 Clinical Research Studies

Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections

Open access
Altarawneh, Heba N., Chemaitelly, Hiam, Ayoub, Houssein H., Tang, Patrick, Hasan, Mohammad R., Yassine, Hadi M., Al-Khatib, Hebah A., Smatti, Maria K. +16 more·2022·New England Journal of Medicine
DOI 10.1056/nejmoa2203965PMC PMC9258753

Published version of a preprint

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Abstract

BACKGROUND: The protection conferred by natural immunity, vaccination, and both against symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection with the BA.1 or BA.2 sublineages of the omicron (B.1.1.529) variant is unclear. METHODS: We conducted a national, matched, test-negative, case-control study in Qatar from December 23, 2021, through February 21, 2022, to evaluate the effectiveness of vaccination with BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna), natural immunity due to previous infection with variants other than omicron, and hybrid immunity (previous infection and vaccination) against symptomatic omicron infection and against severe, critical, or fatal coronavirus disease 2019 (Covid-19). RESULTS: The effectiveness of previous infection alone against symptomatic BA.2 infection was 46.1% (95% confidence interval [CI], 39.5 to 51.9). The effectiveness of vaccination with two doses of BNT162b2 and no previous infection was negligible (-1.1%; 95% CI, -7.1 to 4.6), but nearly all persons had received their second dose more than 6 months earlier. The effectiveness of three doses of BNT162b2 and no previous infection was 52.2% (95% CI, 48.1 to 55.9). The effectiveness of previous infection and two doses of BNT162b2 was 55.1% (95% CI, 50.9 to 58.9), and the effectiveness of previous infection and three doses of BNT162b2 was 77.3% (95% CI, 72.4 to 81.4). Previous infection alone, BNT162b2 vaccination alone, and hybrid immunity all showed strong effectiveness (>70%) against severe, critical, or fatal Covid-19 due to BA.2 infection. Similar results were observed in analyses of effectiveness against BA.1 infection and of vaccination with mRNA-1273. CONCLUSIONS: No discernable differences in protection against symptomatic BA.1 and BA.2 infection were seen with previous infection, vaccination, and hybrid immunity. Vaccination enhanced protection among persons who had had a previous infection. Hybrid immunity resulting from previous infection and recent booster vaccination conferred the strongest protection. (Funded by Weill Cornell Medicine-Qatar and others.).

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Crossref · 10.1056/nejmoa2203965

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Claims the paper makes

0 of 52 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    Among 315 random SARS-CoV-2-positive specimens sequenced, 300 (95.2%) were omicron and 15 (4.8%) were delta.

    “Of these specimens, 300 (95.2%) were confirmed to be omicron infections and 15 (4.8%) to be delta (or B.1.617.2)1 infections.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [2] Altarawneh HN, Chemaitelly H, Hasan MR, et al. Protection against the omicron variant from previous SARS-CoV-2 infection. N Engl J Med 2022; 386: 1288- 1290. 35139269 PMC8849180 source

      Not checked in the free run.

    • cites [3] Chemaitelly H, Ayoub HH, AlMukdad S, et al. Duration of mRNA vaccine protection against SARS-CoV-2 omicron BA.1 and BA.2 subvariants in Qatar. Nat Commun 2022; 13: 3082- 3082. 35654888 PMC9163167 source

      Not checked in the free run.

    • cites [4] Abu-Raddad LJ, Chemaitelly H, Ayoub HH, et al. Effect of mRNA vaccine boosters against SARS-CoV-2 omicron infection in Qatar. N Engl J Med 2022; 386: 1804- 1816. 35263534 PMC8929389 source

      Not checked in the free run.

  • Findingown data

    For symptomatic BA.1 infection, three doses of BNT162b2 with no previous infection had an estimated effectiveness of 59.6% (95% CI, 52.9 to 65.3).

    “The effectiveness of three doses and no previous infection was 59.6% (95% CI, 52.9 to 65.3).”
    Quote in the paperSubstantial claim
  • Findingown data

    For symptomatic BA.2 infection, three doses of BNT162b2 with no previous infection had an estimated effectiveness of 52.2% (95% CI, 48.1 to 55.9).

    “The effectiveness of three doses of BNT162b2 and no previous infection was 52.2% (95% CI, 48.1 to 55.9).”
    Quote in the paperSubstantial claim
  • Findingown data

    For symptomatic BA.1 infection, previous infection plus three doses of BNT162b2 had an estimated effectiveness of 74.4% (95% CI, 63.4 to 82.2).

    “The effectiveness of previous infection and three doses of BNT162b2 was the highest, at 74.4% (95% CI, 63.4 to 82.2).”
    Quote in the paperSubstantial claim
  • Findingown data

    For symptomatic BA.1 infection, previous infection plus two doses of BNT162b2 had an estimated effectiveness of 51.7% (95% CI, 43.5 to 58.7).

    “The effectiveness of hybrid immunity (previous infection and two doses of BNT162b2) was 51.7% (95% CI, 43.5 to 58.7), which was similar to the effectiveness of previous infection alone.”
    Quote in the paperSubstantial claim
  • May combine two claims. 26
  • Classified as probably not a substantial claim. 4

  • May combine two claims.

    Findingown data

    Previous infection, vaccination, and hybrid immunity each showed strong effectiveness greater than 90% against severe, critical, or fatal Covid-19 due to BA.1.

    “Previous infection, vaccination, and hybrid immunity all showed strong effectiveness (>90%) against severe, critical, or fatal Covid-19 due to BA.1 infection, but some of the 95% confidence intervals were wide because of small case numbers (Figure 1B and Table 2).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Among 286 omicron infections with confirmed subvariant status, 68 (23.8%) were BA.1 and 218 (76.2%) were BA.2.

    “Of the 286 omicron infections with confirmed subvariant status, 68 (23.8%) were BA.1 and 218 (76.2%) were BA.2.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Previous infection, vaccination, and hybrid immunity each showed strong effectiveness greater than 70% against severe, critical, or fatal Covid-19 due to BA.2.

    “Previous infection, vaccination, and hybrid immunity all showed strong effectiveness (>70%) against severe, critical, or fatal Covid-19 due to BA.2, but some of the 95% confidence intervals were wide because of small case numbers (Figure 1D and Table 2).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Analysis by time since the immunologic event showed rapid waning of vaccine protection after second and third doses but slow waning of protection from previous infection.

    “The analysis of the effectiveness of previous infection, two-dose vaccination, and three-dose vaccination as a function of time since the immunologic event (previous infection or vaccination) showed rapidly waning vaccine protection after the second and third doses but slowly waning protection from previous infection (Figure 3).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    S-gene target failure is a well-established proxy for BA.1 infection, and non-S-gene target failure is a proxy for BA.2 infection.

    “An S-gene target failure was used as a proxy for BA.1 infection, and a non–S-gene target failure was used as a proxy for BA.2 infection.”
    • Also stated in: § Discussion · boosted
      “Ascertainment of BA.1 and BA.2 infections was based on proxy criteria, but this method of ascertainment is well established.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [24] UK Health Security Agency. SARS-CoV-2 variants of concern and variants under investigation in England: technical briefing 34. January 14, 2022 (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1050236/technical-briefing-34-14-january-2022.pdf).

      Not checked in the free run.

    • cites [29] Abu-Raddad LJ, Chemaitelly H, Ayoub HH, et al. Introduction and expansion of the SARS-CoV-2 B.1.1.7 variant and reinfections in Qatar: a nationally representative cohort study. PLoS Med 2021; 18(12): e1003879- e1003879. 34914711 PMC8726501 source

      Not checked in the free run.

    • cites [30] Challen R, Brooks-Pollock E, Read JM, Dyson L, Tsaneva-Atanasova K, Danon L. Risk of mortality in patients infected with SARS-CoV-2 variant of concern 202012/1: matched cohort study. BMJ 2021; 372: n579- n579. 33687922 PMC7941603 source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductcitation

    The inclusion and exclusion criteria were implemented to allow immunity to build after vaccination and to reduce several potential biases.

    “These inclusion and exclusion criteria were implemented to allow for build-up of immunity after vaccination4,14 and to minimize different types of potential bias, as informed by earlier analyses in the same population.”
    Quote in the paperSubstantial claim0 of 4 sources checked
    • cites [4] Abu-Raddad LJ, Chemaitelly H, Ayoub HH, et al. Effect of mRNA vaccine boosters against SARS-CoV-2 omicron infection in Qatar. N Engl J Med 2022; 386: 1804- 1816. 35263534 PMC8929389 source

      Not checked in the free run.

    • cites [14] 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

      Not checked in the free run.

    • cites [12] Chemaitelly H, Tang P, Hasan MR, et al. Waning of BNT162b2 vaccine protection against SARS-CoV-2 infection in Qatar. N Engl J Med 2021; 385(24): e83- e83. 34614327 PMC8522799 source

      Not checked in the free run.

    • cites [22] Abu-Raddad LJ, Chemaitelly H, Bertollini R. Waning mRNA-1273 vaccine effectiveness against SARS-CoV-2 infection in Qatar. N Engl J Med 2022; 386: 1091- 1093. 35081294 PMC8809505 source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductown data

    The study used a national, matched, test-negative, case-control design in Qatar between December 23, 2021, and February 21, 2022.

    “We conducted a national, matched, test-negative, case–control study in Qatar from December 23, 2021, through February 21, 2022”
    • Also stated in: § Study Design · plain
      “We used a test-negative, case–control design, in which effectiveness estimates were derived by comparing the odds of previous infection or vaccination or both among case participants (persons with a positive PCR test) with that among controls (PCR-negative persons).”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Study design and conductreasoning

    For severe, critical, or fatal Covid-19 outcomes, a one-to-five matching ratio was used to improve statistical precision.

    “To assess effectiveness against any severe, critical, or fatal case of Covid-19, we used a 1:5 matching ratio to improve the statistical precision of the estimates.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductcitation

    Severe, critical, and fatal Covid-19 cases were classified according to World Health Organization guidelines and assessed by trained medical personnel using individual chart reviews.

    “Classification of severe,8 critical,8 and fatal9 Covid-19 cases followed World Health Organization guidelines, and assessments were made by trained medical personnel with the use of individual chart reviews as part of a national protocol applied to hospitalized patients with Covid-19.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [8] World Health Organization. Living guidance for clinical management of COVID-19. November 23, 2021 (https://www.who.int/publications/i/item/WHO-2019-nCoV-clinical-2021-2).

      Not checked in the free run.

    • cites [9] World Health Organization. International guidelines for certification and classification (coding) of COVID-19 as cause of death. April 20, 2020 (https://www.who.int/publications/m/item/international-guidelines-for-certification-and-classification-%28coding%29-of-covid-19-as-cause-of-death).

      Not checked in the free run.

  • May combine two claims.

    Study design and conductown data

    Rapid antigen testing was broadly implemented and probably did not differentially affect PCR testing to introduce bias, as supported by the sensitivity analysis and minimal differences between PCR and rapid antigen tests by exposure category.

    “However, rapid antigen testing was broadly implemented and probably did not differentially affect PCR testing to introduce bias, as supported by the sensitivity analysis (Table S3) and the minimal differences between PCR and rapid antigen tests according to exposure category (Table S7).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductown data

    Some omicron infections may have been misclassified delta infections, but delta incidence was limited during the study period.

    “Some omicron infections may have been misclassified delta infections, but the incidence of delta was limited during the study period (Section S2).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    Most persons received their third dose less than 45 days earlier, which may explain the relatively high effectiveness.

    “However, most persons received their third dose less than 45 days earlier, perhaps explaining the relatively high effectiveness.3”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [3] Chemaitelly H, Ayoub HH, AlMukdad S, et al. Duration of mRNA vaccine protection against SARS-CoV-2 omicron BA.1 and BA.2 subvariants in Qatar. Nat Commun 2022; 13: 3082- 3082. 35654888 PMC9163167 source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductcitation

    Effectiveness was assessed with a test-negative case-control design rather than a cohort design, but an earlier cohort study in the same population yielded similar findings.

    “Effectiveness was assessed with the use of an observational, test-negative, case–control design rather than a design in which cohorts of individual persons were followed up. However, the cohort study design applied earlier to the same population yielded findings similar to those of the test-negative design.14,15,31”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [14] 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

      Not checked in the free run.

    • cites [15] Chemaitelly H, Yassine HM, Benslimane FM, et al. mRNA-1273 COVID-19 vaccine effectiveness against the B.1.1.7 and B.1.351 variants and severe COVID-19 disease in Qatar. Nat Med 2021; 27: 1614- 1621. 34244681 source

      Not checked in the free run.

    • cites [31] Butt AA, Chemaitelly H, Al Khal A, et al. SARS-CoV-2 vaccine effectiveness in preventing confirmed infection in pregnant women. J Clin Invest 2021; 131(23): e153662- e153662. 34618693 PMC8631593 source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    Two-dose vaccination with no previous infection had negligible effectiveness against BA.1 and BA.2, but most persons had received their second dose more than eight months earlier.

    “Two-dose vaccination and no previous infection had negligible effectiveness against BA.1 and BA.2, but most persons received their second dose more than 8 months earlier.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Protection from hybrid immunity of previous infection plus two-dose vaccination was similar to that from previous infection alone, at approximately 50%, suggesting that the protection originated from the previous infection rather than from vaccination.

    “The protection conferred by hybrid immunity of previous infection and two-dose vaccination was similar to that of previous infection alone, at approximately 50%, which suggests that this protection originated from the previous infection and not from vaccination.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The findings are explained by short-lived protection of primary-series vaccination against omicron and more durable protection from natural infection.

    “These findings are explained by the short-lived protection of primary-series vaccination against omicron infections3,27 and the more durable protection from natural infection,2,28 as confirmed by the additional analysis of protection as a function of time after previous infection or vaccination (Figure 3).”
    Quote in the paperSubstantial claim0 of 4 sources checked
    • cites [3] Chemaitelly H, Ayoub HH, AlMukdad S, et al. Duration of mRNA vaccine protection against SARS-CoV-2 omicron BA.1 and BA.2 subvariants in Qatar. Nat Commun 2022; 13: 3082- 3082. 35654888 PMC9163167 source

      Not checked in the free run.

    • cites [27] Andrews N, Stowe J, Kirsebom F, et al. Covid-19 vaccine effectiveness against the omicron (B.1.1.529) variant. N Engl J Med 2022; 386: 1532- 1546. 35249272 PMC8908811 source

      Not checked in the free run.

    • cites [2] Altarawneh HN, Chemaitelly H, Hasan MR, et al. Protection against the omicron variant from previous SARS-CoV-2 infection. N Engl J Med 2022; 386: 1288- 1290. 35139269 PMC8849180 source

      Not checked in the free run.

    • cites [28] Chemaitelly H, Ayoub HH, AlMukdad S, et al. Protection of prior natural infection compared to mRNA vaccination against SARS-CoV-2 infection and severe COVID-19 in Qatar. March 18, 2022 (https://www.medrxiv.org/content/10.1101/2022.03.17.22272529v1). preprint. PMC9651957 36375482 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Study design and conductnone given

    One cannot rule out the possibility that bias could arise in unexpected ways or from unknown sources in real-world data.

    “Nonetheless, one cannot rule out the possibility that in real-world data, bias could arise in unexpected ways or from unknown sources, such as subtle differences or changes in test-seeking behavior.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductown data

    A sensitivity analysis that counted rapid antigen-positive results as previous positive testing produced findings similar to the main analyses, indicating that excluding previous rapid antigen-positive tests may not have biased the estimates.

    “A sensitivity analysis in which previous positive testing included both PCR-positive and rapid antigen–positive results showed similar findings to those of the main analyses, which indicates that exclusion of previous rapid antigen–positive tests may not have biased our estimates (Table S3).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationcitation

    The findings were consistent with those of other studies of vaccine effectiveness against omicron infection.

    “Notwithstanding these limitations, findings were consistent with those of other studies of vaccine effectiveness against omicron infection (BA.1 or BA.2 subvariants were not specified).27,32-36”
    Quote in the paperNot a substantial claim0 of 6 sources checked
    • cites [27] Andrews N, Stowe J, Kirsebom F, et al. Covid-19 vaccine effectiveness against the omicron (B.1.1.529) variant. N Engl J Med 2022; 386: 1532- 1546. 35249272 PMC8908811 source

      Not checked in the free run.

    • cites [32] Buchan SA, Chung H, Brown KA, et al. Effectiveness of COVID-19 vaccines against omicron or delta infection. January 1, 2022 (https://www.medrxiv.org/content/10.1101/2021.12.30.21268565v1). preprint. PMC9500552 36136332 source

      Not checked in the free run.

    • cites [33] Hansen CH, Schelde AB, Moustsen-Helm IR, et al. Vaccine effectiveness against SARS-CoV-2 infection with the omicron or delta variants following a two-dose or booster BNT162b2 or mRNA-1273 vaccination series: a Danish cohort study. December 21, 2021 (https://www.medrxiv.org/content/10.1101/2021.12.20.21267966v1). preprint. source

      Not checked in the free run.

    • cites [34] Patalon T, Saciuk Y, Peretz A, et al. Waning effectiveness of the third dose of the BNT162b2 mRNA COVID-19 vaccine. February 26, 2022 (https://www.medrxiv.org/content/10.1101/2022.02.25.22271494v1). preprint. PMC9184525 35680872 source

      Not checked in the free run.

    • cites [35] Šmíd M, Berec L, Májek O, et al. Protection by vaccines and previous infection against the omicron variant of SARS-CoV-2. February 25, 2022 (https://www.medrxiv.org/content/10.1101/2022.02.24.22271396v1). preprint. PMC9129207 35482442 source

      Not checked in the free run.

    • cites [36] Tseng HF, Ackerson BK, Luo Y, et al. Effectiveness of mRNA-1273 against SARS-CoV-2 omicron and delta variants. Nat Med 2022; 28: 1063- 1071. 35189624 PMC9117141 source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    All five forms of immunity investigated showed strong protection against Covid-19-related hospitalization and death, with effectiveness greater than 70%.

    “Even though the five forms of immunity investigated showed large differences in protection against symptomatic infection that ranged from 0 to 80%, they all showed strong protection against Covid-19–related hospitalization and death, at an effectiveness of more than 70%.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductown data

    Extensive sensitivity and additional analyses were conducted to investigate potential bias in earlier studies using similar methods, and these analyses showed consistent findings.

    “Extensive sensitivity and additional analyses were conducted to investigate effects of potential bias in our earlier studies that used similar methods. These included different adjustments and controls in the analysis and different study inclusion and exclusion criteria to investigate whether effectiveness estimates could have been biased.12,22 These analyses showed consistent findings.2,3,12,17,2”
    Quote in the paperNot a substantial claim0 of 5 sources checked
    • cites [12] Chemaitelly H, Tang P, Hasan MR, et al. Waning of BNT162b2 vaccine protection against SARS-CoV-2 infection in Qatar. N Engl J Med 2021; 385(24): e83- e83. 34614327 PMC8522799 source

      Not checked in the free run.

    • cites [22] Abu-Raddad LJ, Chemaitelly H, Bertollini R. Waning mRNA-1273 vaccine effectiveness against SARS-CoV-2 infection in Qatar. N Engl J Med 2022; 386: 1091- 1093. 35081294 PMC8809505 source

      Not checked in the free run.

    • cites [2] Altarawneh HN, Chemaitelly H, Hasan MR, et al. Protection against the omicron variant from previous SARS-CoV-2 infection. N Engl J Med 2022; 386: 1288- 1290. 35139269 PMC8849180 source

      Not checked in the free run.

    • cites [3] Chemaitelly H, Ayoub HH, AlMukdad S, et al. Duration of mRNA vaccine protection against SARS-CoV-2 omicron BA.1 and BA.2 subvariants in Qatar. Nat Commun 2022; 13: 3082- 3082. 35654888 PMC9163167 source

      Not checked in the free run.

    • cites [17] Ayoub HH, Tomy M, Chemaitelly H, et al. Estimating protection afforded by prior infection in preventing reinfection: applying the test-negative study design. January 3, 2022 (https://www.medrxiv.org/content/10.1101/2022.01.02.22268622v1). preprint. PMC11145912 38061757

      Not checked in the free run.

  • May combine two claims.

    Study design and conductcitation

    Matching was not possible for coexisting conditions, but matching on sex, age, and nationality provided demonstrable control of bias in earlier studies.

    “Although matching was performed according to sex, age, and nationality, matching was not possible for other factors, such as coexisting conditions. However, matching according to these factors provided demonstrable control of bias in our earlier studies.11,12,15,21,22”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [11] Abu-Raddad LJ, Chemaitelly H, Bertollini R. Effectiveness of mRNA-1273 and BNT162b2 vaccines in Qatar. N Engl J Med 2022; 386: 799- 800. 35045222 PMC8796790 source

      Not checked in the free run.

    • cites [12] Chemaitelly H, Tang P, Hasan MR, et al. Waning of BNT162b2 vaccine protection against SARS-CoV-2 infection in Qatar. N Engl J Med 2021; 385(24): e83- e83. 34614327 PMC8522799 source

      Not checked in the free run.

    • cites [15] Chemaitelly H, Yassine HM, Benslimane FM, et al. mRNA-1273 COVID-19 vaccine effectiveness against the B.1.1.7 and B.1.351 variants and severe COVID-19 disease in Qatar. Nat Med 2021; 27: 1614- 1621. 34244681 source

      Not checked in the free run.

    • cites [21] Abu-Raddad LJ, Chemaitelly H, Yassine HM, et al. Pfizer-BioNTech mRNA BNT162b2 Covid-19 vaccine protection against variants of concern after one versus two doses. J Travel Med 2021; 28(7): taab083- taab083. 34050372 PMC8194836 source

      Not checked in the free run.

    • cites [22] Abu-Raddad LJ, Chemaitelly H, Bertollini R. Waning mRNA-1273 vaccine effectiveness against SARS-CoV-2 infection in Qatar. N Engl J Med 2022; 386: 1091- 1093. 35081294 PMC8809505 source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductcitation

    Ascertainment of BA.1 and BA.2 infections used proxy criteria, but this method is well established.

    “Ascertainment of BA.1 and BA.2 infections was based on proxy criteria, but this method of ascertainment is well established.24,29,30”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [24] UK Health Security Agency. SARS-CoV-2 variants of concern and variants under investigation in England: technical briefing 34. January 14, 2022 (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1050236/technical-briefing-34-14-january-2022.pdf).

      Not checked in the free run.

    • cites [29] Abu-Raddad LJ, Chemaitelly H, Ayoub HH, et al. Introduction and expansion of the SARS-CoV-2 B.1.1.7 variant and reinfections in Qatar: a nationally representative cohort study. PLoS Med 2021; 18(12): e1003879- e1003879. 34914711 PMC8726501 source

      Not checked in the free run.

    • cites [30] Challen R, Brooks-Pollock E, Read JM, Dyson L, Tsaneva-Atanasova K, Danon L. Risk of mortality in patients infected with SARS-CoV-2 variant of concern 202012/1: matched cohort study. BMJ 2021; 372: n579- n579. 33687922 PMC7941603 source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductown data

    BA.1 or BA.2 ascertainment was not possible for a minority of infections, but this may not have biased results because infections with and without ascertainment had a similar distribution across exposure categories.

    “Ascertainment of BA.1 and BA.2 infections was not possible for a minority of infections. However, this may not have biased our results, since both infections with and without BA.1 or BA.2 ascertainment had a similar distribution among exposure categories (Table S6).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    The results confirmed other findings: approximately 50% protection from previous infection against BA.1 reinfection, approximately 50% protection from mRNA boosters compared with primary series, and negligible mRNA vaccine effectiveness against omicron infection six or more months after the second dose.

    “The results confirmed other findings that we reported recently, including a protection of approximately 50% for previous infection against reinfection with BA.1,2 a protection of approximately 50% for mRNA boosters as compared with primary series,4 and the finding that mRNA vaccines have negligible effectiveness against omicron infection 6 or more months after the second dose.3”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [2] Altarawneh HN, Chemaitelly H, Hasan MR, et al. Protection against the omicron variant from previous SARS-CoV-2 infection. N Engl J Med 2022; 386: 1288- 1290. 35139269 PMC8849180 source

      Not checked in the free run.

    • cites [4] Abu-Raddad LJ, Chemaitelly H, Ayoub HH, et al. Effect of mRNA vaccine boosters against SARS-CoV-2 omicron infection in Qatar. N Engl J Med 2022; 386: 1804- 1816. 35263534 PMC8929389 source

      Not checked in the free run.

    • cites [3] Chemaitelly H, Ayoub HH, AlMukdad S, et al. Duration of mRNA vaccine protection against SARS-CoV-2 omicron BA.1 and BA.2 subvariants in Qatar. Nat Commun 2022; 13: 3082- 3082. 35654888 PMC9163167 source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    No notable differences were observed in the effectiveness against BA.1 and BA.2 of previous infection, vaccination, and hybrid immunity.

    “No notable differences were observed in the effectiveness against BA.1 and BA.2 of previous infection, vaccination, and hybrid immunity.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Protection from previous infection with variants other than omicron against reinfection was moderate and durable, but protection from primary-series vaccination against infection was negligible by six months after the second dose.

    “Protection from previous infection with variants other than omicron against reinfection was moderate and durable, but protection of primary-series vaccination against infection was negligible by 6 months after the second dose.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Recent booster vaccination had moderate effectiveness, whereas hybrid immunity from previous infection and recent booster vaccination conferred the strongest protection against infection, at approximately 80%.

    “Recent booster vaccination had moderate effectiveness, whereas hybrid immunity from previous infection and recent booster vaccination conferred the strongest protection against infection, at approximately 80%.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    All five forms of immunity were associated with strong and durable protection against Covid-19-related hospitalization and death.

    “All five forms of immunity were associated with strong and durable protection against Covid-19–related hospitalization and death.”
    Quote in the paperSubstantial claim
29 of 29

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?

  • Under a sensitivity analysis assuming naturally acquired immunity decayed to 75% in 100 days, population immunity by 31 July 2022 was 36% (31-41%).

    “Sensitivity analyses assuming exponentially decaying immunity from natural infection yielded population immunity of 48% (42–54%) or 36% (31–41%) if such naturally acquired immunity decayed to 85% in 365 days15 or to 75% in 100 days16,17, respectively”

    From Real-world COVID-19 vaccine effectiveness against the Omicron BA.2 variant in a SARS-CoV-2 infection-naive population (2023) · cites this paper as [17]

    The Results report effectiveness against symptomatic Omicron infection, and the study ended on February 21, 2022 (Results, Study Population; page unavailable). Searches for the 75%-in-100-days assumption and the July 31 population-immunity estimate found no passage in our copy addressing either figure. (LLM, conf=0.76)

    Experimental — accuracy not yet measured

  • Prior work has demonstrated Omicron BA.1/2's significant immune escape properties.

    “Prior work has demonstrated Omicron BA. 1/2's significant immune escape properties [13][14][15][16][17] .”

    From Rapidly shifting immunologic landscape and severity of SARS-CoV-2 in the Omicron era in South Africa (2023) · cites this paper as [13]

No citation lists for this paper

No citation lists for this paper yet — checked again daily.

References 44 · Cited by 551

Research works printed but not linked: 2

  1. Ayoub HH Tomy M Chemaitelly H et al. Estimating protection afforded by prior infection in preventing reinfection: applying the test-negative study design. January 3 2022 (https://www.medrxiv.org/content/10.1101/2022.01.02.22268622v1). preprint. · DOI
  2. Buchan SA Chung H Brown KA et al. Effectiveness of COVID-19 vaccines against omicron or delta infection. January 1 2022 (https://www.medrxiv.org/content/10.1101/2021.12.30.21268565v1). preprint. · DOI · Paper page

Authors
Altarawneh, H. N., Chemaitelly, H., Ayoub, H. H., Tang, P., Hasan, M. R., Yassine, H. M., Al-Khatib, H. A., Smatti, M. K., Coyle, P., Al-Kanaani, Z., Al-Kuwari, E., Jeremijenko, A., Kaleeckal, A. H., Latif, A. N., Shaik, R. M., Abdul-Rahim, H. F., Nasrallah, G. K., Al-Kuwari, M. G., Butt, A. A., Al-Romaihi, H. E., Al-Thani, M. H., Al-Khal, A., Bertollini, R., & Abu-Raddad, L. J.
Affiliations
  • Cornell University (US)
  • Queen's University Belfast (GB)
  • From the Infectious Disease Epidemiology Group and the World Health Organization Collaborating Center for Disease Epidemiology Analytics on HIV/AIDS, Sexually Transmitted Infections, and Viral Hepatitis, Weill Cornell Medicine–Qatar, Cornell University, Education City (H.N.A., H.C., L.J.A.-R.), the Mathematics Program, Department of Mathematics, Statistics, and Physics, College of Arts and Sciences (H.H.A.), the Biomedical Research Center (H.M.Y., H.A.A.-K., M.K.S., P.C., G.K.N.), and the Departments of Biomedical Science (H.M.Y., H.A.A.-K., M.K.S., G.K.N.) and Public Health (H.F.A.-R., L.J.A.-R.), College of Health Sciences, QU Health, Qatar University, the Department of Pathology, Sidra Medicine (P.T., M.R.H.), Hamad Medical Corporation (P.C., Z.A.-K., E.A.-K., A.J., A.H.K., A.N.L., R.M.S., A.A.B., A.A.-K.), Primary Health Care Corporation (M.G.A.-K.), and the Ministry of Public Health (H.E.A.-R., M.H.A.-T., R.B.) — all in Doha, Qatar; the Departments of Population Health Sciences (H.N.A., H.C., A.A.B., ...
Corresponding author
Abu-Raddad, Laith J.
ORCID
Venue
New England Journal of Medicine
Publisher
Massachusetts Medical Society
Published
2022-07-07
Volume
387
Issue
1
Pages
21-34
ISSN
  • 0028-4793 (ISSN-L)
  • 1533-4406
DOI
10.1056/nejmoa2203965
PMC
PMC9258753
OpenAlex
W4282958946
Cited by
551
References
44
Citations by year
2026: 29 · 2025: 59 · 2024: 117 · 2023: 190 · 2022: 156
FWCI
63.92
Type
journal article
Language
en
Open access
Licence
www.nejmgroup.org/legal/terms-of-use.htm (vor)
Locations
  • New England Journal of Medicine (publishedVersion)
  • medRxiv (acceptedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • Qatar University QSpace (Qatar University) (submittedVersion)
Funders
  • Biomedical Research Program and the Biostatistics, Epidemiology, and Biomathematics Research Core, both at Weill Cornell Medicine-Qatar
  • Ministry of Public Health, Hamad Medical Corporation, and Sidra Medicine
  • Qatar Genome Programme and Qatar University Biomedical Research Center
Topics
  • Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
  • Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
  • Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
Keywords
Omicron variant, BA.1, BA.2, hybrid immunity, natural immunity, prior SARS-CoV-2 infection, COVID-19 vaccination, BNT162b2, mRNA-1273, vaccine effectiveness, symptomatic infection, severe COVID-19 outcomes, critical illness, fatal COVID-19
MeSH terms
COVID-19, SARS-CoV-2, BNT162 Vaccine, 2019-nCoV Vaccine mRNA-1273, Humans, Immunity, Innate, Immunization, Immunization, Secondary, Recurrence, Vaccination, Case-Control Studies

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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.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-06.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-06.

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