By Tanya Terry
A comparison of COVID-19 mortality rates among adults 65 and over who were unvaccinated and those who received a bivalent booster dose within the preceding six months was the topic of The Centers of Disease and Prevention’s (CDC’s) Morbidity and Mortality Weekly Report released June 16. Similarly to other studies assessing vaccine effectiveness against critical illness and death, the report showed receipt of a bivalent booster dose provided substantial protection against COVID-19–associated death for those in the age group it focused on.
For the report, the CDC estimated mortality rate ratios among unvaccinated people and among those who received bivalent boosters by time since vaccination during three periods of Omicron lineage predominance. The periods looked at were September 18-November 5, 2022, as the time of BA.5 predominance; November 6, 2022-January 21, 2023, as the period of BQ.1/BQ.1.1 and January 22-April 1, 2023 as the period of XBB.1.5 predominance.
Weekly counts of COVID-19-associated deaths and those who received a bivalent booster dose were reported from 20 jurisdictions between September 18, 2022, and April 1, 2023.
The mortality rate ratios were found by dividing rates among unvaccinated people by rates among bivalent booster dose recipients. Average weekly mortality rates were estimated based on data of specimen collection during each variant period by vaccination status and times since bivalent booster dose receipt. For deaths that were not laboratory-confirmed, alternate reference dates were used in lieu of positive specimen collection date (i.e. symptom onset date or date of death or report date when symptom onset date was unavailable.) After detrending the linear changes in weekly rates, rate ratios were calculated by dividing rates among unvaccinated people by rates among bivalent booster recipients.
There were 8,161 combined COVID-19-related deaths over the 20 jurisdictions between September 18, 2022 and April 1, 2023 among those 65 and older who either received a bivalent COVID-19 vaccine booster or those in that age group who were completely unvaccinated from COVID-19.
Among the findings of the report was that higher mortality rates were observed among unvaccinated people during all three periods of Omicron lineage predominance.
Time-stratified mortality rates among unvaccinated and vaccinated people two weeks to two months after receiving a bivalent booster vaccination were also reported by the CDC. They found what represented a moderate decline in vaccine effectiveness between the BA.5- and XBB.1.5-predominant period from 16.3 to 8.4.
However, mortality rates ratios were similar in people who received a bivalent vaccination two weeks to two months earlier or between three and six months before the BQ.1/BQ.1.1-the XBB. 1.5-predominant periods. Those rates rations were 11.4 and 11.0 and 8.4 and 7.3 respectively.
The report showed not only that bivalent COVID-19 booster vaccination provides substantial protection against COVID deaths in adults ages 65 and over, but similarly to other reports evaluating vaccine effectiveness, that there is no evidence of waning up to six months post vaccination.
The CDC recommends all persons stay up to date with recommended COVID-19 vaccines, including one or more bivalent dose for those aged 6 months and over. Additional bivalent vaccine doses are optional for adults aged 65 years and over and immunocompromised persons. The CDC first recommended bivalent COVID-19 vaccines for the elderly living in the United States on September 1, 2022.
Source: Johnson AG, et al. 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.
