This page summarizes a CDC report on the bivalent mRNA COVID-19 boosters of 2022–2023, using hospital data from September 13, 2022 to April 21, 2023. Vaccine products and recommendations have changed since; check CDC for current guidance.
On September 1, 2022, CDC's Advisory Committee on Immunization Practices recommended one bivalent mRNA COVID-19 booster for everyone aged 12 and older who had finished at least a monovalent primary series. Early results showed the booster added protection, but it was too soon to tell how long that would last.
The study
CDC's VISION Network looked at adults hospitalized with COVID-19–like illness at five sites in seven states: HealthPartners (Minnesota and Wisconsin), Intermountain Healthcare (Utah), Kaiser Permanente Northern California, Kaiser Permanente Center for Health Research (Oregon and Washington) and the Regenstrief Institute (Indiana).
- Design: test-negative case-control. Patients who tested positive for SARS-CoV-2 were compared with those who tested negative, by vaccination status.
- Groups: unvaccinated; monovalent doses only; or one bivalent booster received 7–59, 60–119 or 120–179 days earlier.
- Adjusted for age, race and ethnicity, sex, calendar day and region, and analyzed separately for people with and without immunocompromising conditions (identified from discharge codes).
- Critical illness meant ICU admission or death in the hospital or within 28 days of admission.
Results
Adults without immunocompromising conditions: 66,141 hospitalizations, 6,907 of them COVID-19 case-patients.
| Time since bivalent booster | Effectiveness against hospitalization | Against critical illness |
|---|---|---|
| 7–59 days | 62% (95% CI 57%–67%) | 69% |
| 120–179 days | 24% (95% CI 12%–33%) | 50% |
| Monovalent doses only (median 376 days since last dose) | 21% |
Effectiveness against hospitalization was similar across age groups. Waning showed from 60 to 179 days (2–6 months) after the booster, the same pattern seen after monovalent doses during Omicron: high at first, then falling. Protection against critical illness held up better, consistent with earlier CDC findings that monovalent mRNA vaccines gave durable protection against the most severe outcomes.
Adults with immunocompromising conditions: 18,934 hospitalizations (22.3% of the total), 1,834 of them case-patients.
| Time since bivalent booster | Effectiveness against hospitalization |
|---|---|
| 7–59 days | 28% (95% CI 10%–42%) |
| 120–179 days | 13% |
| Monovalent doses only (median 355 days) | 3% |
Effectiveness was lower in this group but did not clearly wane, perhaps because immune responses vary widely among people with these conditions, or because the study lacked the power to detect a change. It also lacked the power to compare types of conditions.
What it meant at the time
- As of May 10, 2023, only one in five U.S. adults (20.5%) had received a bivalent booster. Most who had only monovalent doses had their last one more than a year earlier, and may have kept relatively little protection against hospitalization, though more against critical illness.
- On April 19, 2023, CDC allowed adults aged 65 and older and people with immunocompromising conditions to get one or more additional bivalent doses. Waning was the same in younger and older adults, but hospitalization and death rates remained much higher in older adults, suggesting an extra dose might help. People with immunocompromising conditions also remained at higher risk and might benefit, though that needed further study.
- The authors' conclusion: everyone eligible should stay up to date with recommended COVID-19 vaccines.
Limitations
- Prior infection was not accounted for. Much of the population had been infected, and that immunity lowers the risk of illness, so the results show vaccination's added benefit on top of it.
- Incidental cases: some case-patients may have been hospitalized for other reasons while having mild COVID-19, which would lower measured effectiveness.
- Residual confounding is possible, from behavior, prior infection or treatments such as nirmatrelvir-ritonavir (Paxlovid).
- Effectiveness could not be compared by sublineage or by vaccine product.
- Data from seven states may not represent the whole country.
Sources
- Link-Gelles R, Weber ZA, Reese SE, et al. "Estimates of Bivalent mRNA Vaccine Durability in Preventing COVID-19–Associated Hospitalization and Critical Illness Among Adults with and Without Immunocompromising Conditions — VISION Network, September 2022–April 2023." MMWR 72(21). https://www.cdc.gov/mmwr/volumes/72/wr/mm7221a3.htm
- Supplementary table: https://stacks.cdc.gov/view/cdc/128421
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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