Bivalent COVID-19 Boosters Kept Protecting Older Adults Against Death for 6 Months

Updated, bivalent COVID-19 vaccines were first recommended on September 1, 2022, and an early analysis showed a bivalent booster added protection against infection and death. The question that followed was how long that protection lasted. For adults 65 and older, the answer from this CDC follow-up: substantial protection against death, with no significant sign of waning for up to six months — though a newer variant chipped away at it slightly.

The data

From September 18, 2022, to April 1, 2023, 20 jurisdictions that link case reports to immunization registries and death records — together about 41 percent of the U.S. population — reported weekly COVID-19 deaths among people 65 and older who were either unvaccinated or had a bivalent booster. There were 8,161 deaths; 58 percent were among people 80 and older, a share that held across vaccination status and time. Death rates peaked in December 2022, and were higher among the unvaccinated throughout.

The analysis compared death rates in three periods, each dominated by a different Omicron lineage:

What it means

• No significant waning. Within each period, people boosted 3 to 6 months earlier were about as protected as those boosted more recently — consistent with other studies of protection against critical illness and death.
• Some immune escape. From the BA.5 period to the XBB.1.5 period, the crude vaccine effectiveness against death among recently boosted people fell from 94 percent to 88 percent, likely because XBB.1.5's spike protein had drifted from the BA.4/BA.5 spike in the bivalent vaccine — relevant to future vaccine composition.

At the time, CDC advised everyone aged 6 months and older to stay up to date, including at least one bivalent dose, with additional bivalent doses optional for adults 65 and older and people with weakened immune systems. With the end of the COVID-19 public health emergency on May 11, 2023, routine monitoring of cases, hospitalizations and deaths by vaccination status stopped; CDC continues to track effectiveness through studies such as the VISION and IVY networks.

Limits

This was an ecologic study of surveillance data, so it could not adjust for prior infection, other illnesses, or testing and prevention habits. Deaths fell during the XBB.1.5 period, limiting statistical power. Only 7 of the 20 jurisdictions counted deaths without laboratory confirmation. Bivalent and original boosters may sometimes have been misclassified; 0.3 percent of people got a second bivalent dose before it was authorized for some groups. And the data may not represent the rest of the country.

Sources

Based on "Notes from the Field: Comparison of COVID-19 Mortality Rates Among Adults Aged ≥65 Years Who Were Unvaccinated and Those Who Received a Bivalent Booster Dose Within the Preceding 6 Months — 20 U.S. Jurisdictions, September 18, 2022–April 1, 2023," by Amelia G. Johnson and colleagues (CDC and state and local health departments), Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention; a work of the United States government in the public domain.