Assessing vaccine effectiveness against severe COVID-19 disease caused by omicron variant. Report from a meeting of the World Health Organization
Open accessAbstract
Vaccine effectiveness is lower and wanes faster against infection and symptomatic disease caused by the omicron variant of SARS-CoV-2 than was observed with previous variants. Vaccine effectiveness against severe omicron disease, on average, is higher, but has shown variability, including rapid apparent waning, in some studies. Assessing vaccine effectiveness against omicron severe disease using hospital admission as a measure of severe disease has become more challenging because of omicron's attenuated intrinsic severity and its high prevalence of infection. Many hospital admissions likely occur among people with incidental omicron infection or among those with infection-induced exacerbation of chronic medical conditions. To address this challenge, the World Health Organization held a virtual meeting on March 15, 2022, to review evidence from several studies that assessed Covid-19 vaccine effectiveness against severe omicron disease using several outcome definitions. Data was shown from studies in South Africa, the United States, the United Kingdom and Qatar. Several approaches were proposed that better characterize vaccine protection against severe Covid-19 disease caused by the omicron variant than using hospitalization of omicron-infected persons to define severe disease. Using more specific definitions for severe respiratory Covid-19 disease, such as indicators of respiratory distress (e.g. oxygen requirement, mechanical ventilation, and ICU admission), showed higher vaccine effectiveness than against hospital admission. Second, vaccine effectiveness against progression from omicron infection to hospitalization, or severe disease, also showed higher vaccine protection. These approaches might better characterize vaccine performance against severe Covid-19 disease caused by omicron, as well as future variants that evade humoral immunity, than using hospitalization with omicron infection as an indicator of severe disease.
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Including incidental infections or exacerbations in hospitalization-based severe disease definitions would result in a lower vaccine effectiveness against hospitalization if vaccine effectiveness is truly lower against BA.4/5 infection.
“both of which would result in a lower VE against hospitalization if VE is truly lower against BA.4/5 infection [37].”
From Assessing COVID-19 vaccine effectiveness against Omicron subvariants: Report from a meeting of the World Health Organization (2023) · cites this paper as [37]
The sections “Hospitalization with omicron infection rather than for omicron disease” and “Summary and conclusions” explain that incidental infections and exacerbations can make hospitalization-based estimates lower than estimates for severe COVID-19 disease. “Approaches to evaluating vaccine effectiveness” also states that lower effectiveness against omicron infection can lower apparent effectiveness against hospitalization. The paper does not specifically address BA.4/5, so it supports the conditional reasoning but not its application to that subvariant. (LLM, conf=0.84)
Experimental — accuracy not yet measuredA larger percentage of hospitalizations during the Omicron period likely had incidental, rather than causal, infections with SARS-CoV-2.
“Additionally, a larger percentage of hospitalizations during the Omicron period likely had incidental, rather than causal, infections with SARS-CoV-2”
From Assessing COVID-19 vaccine effectiveness against Omicron subvariants: Report from a meeting of the World Health Organization (2023) · cites this paper as [37]
Infections would be more affected by true waning of vaccine effectiveness than hospitalizations.
“and infections would be more affected by true waning of VE [37,41].”
From Assessing COVID-19 vaccine effectiveness against Omicron subvariants: Report from a meeting of the World Health Organization (2023) · cites this paper as [37]
Definitions of severe disease that rely solely on hospitalization might include persons hospitalized with incidental Omicron infection or exacerbations of underlying illness triggered by SARS-CoV-2 infection.
“Alternatively, definitions of severe disease that rely solely on hospitalization might in fact include persons hospitalized with incidental Omicron infection or exacerbations of underlying illness triggered by SARS-CoV2 infection”
From Assessing COVID-19 vaccine effectiveness against Omicron subvariants: Report from a meeting of the World Health Organization (2023) · cites this paper as [37]
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“Additionally, a larger percentage of hospitalizations during the Omicron period likely had incidental, rather than causal, infections with SARS-CoV-2, and infections would be more affected by true waning of VE [37,41].”
Self-citation
- Authors
- Feikin, D. R., Abu-Raddad, L. J., Andrews, N., Davies, M.-A., Higdon, M. M., Orenstein, W. A., & Patel, M. K.
- Affiliations
- World Health Organization (CH)
- Cornell University (US)
- UK Health Security Agency (GB)
- Western Cape Department of Health (ZA)
- Johns Hopkins University (US)
- Emory University (US)
- Corresponding author
- Feikin, Daniel R.
- ORCID
- Venue
- Vaccine
- Publisher
- Elsevier BV
- Published
- 2022-06
- Volume
- 40
- Issue
- 26
- Pages
- 3516-3527
- ISSN
- 0264-410X (ISSN-L)
- PMC
- PMC9058052
- OpenAlex
- W4225285640
- Cited by
- 83
- References
- 26
- Citations by year
- 2026: 4 · 2025: 5 · 2024: 15 · 2023: 40 · 2022: 19
- FWCI
- 9.66
- Type
- journal article
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- Locations
- Vaccine (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Funders
- World Health Organization
- Centers for Disease Control and Prevention
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Keywords
- COVID-19 vaccine effectiveness, Omicron variant, severe COVID-19, hospitalization, respiratory distress, mechanical ventilation, intensive care unit admission, vaccine waning, immune evasion
- MeSH terms
- COVID-19, SARS-CoV-2, COVID-19 Vaccines, Vaccine Efficacy, Humans, United States, World Health Organization
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