In a recent Morbidity and Mortality Weekly Report (MMWR), america Centers for Disease Control and Prevention (CDC) reported how coronavirus disease 2019 (COVID-19) mortality rates varied amongst unvaccinated and vaccinated adults aged ≥65 years in america between 2022 and 2023.

Study: Notes from the Field: Comparison of COVID-19 Mortality Rates Amongst Adults Aged ≥65 Years Who Were Unvaccinated and Those Who Received a Bivalent Booster Dose Inside the Preceding 6 Months — 20 U.S. Jurisdictions, September 18, 2022–April 1, 2023. Image Credit: GroundPicture/Shutterstock.com

Background

The CDC really useful bivalent COVID-19 vaccines for the primary time on September 1, 2022, for the elderly population of the U.S.

Following these vaccine programs, studies analyzed COVID-19 cases and mortality rates by vaccination status soon after authorization of bivalent COVID-19 vaccines, which showed these vaccines conferred additional protection.

In regards to the report

This follow-up CDC report compiled data on the effect and sturdiness of bivalent COVID-19 booster vaccine amongst adults aged ≥65 years. Specifically, they estimated mortality rate ratios (RRs) in vaccinated people by time since bivalent vaccination during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant’s predominance periods. 

Omicron BA.5 dominated the period between September 18 and November 5, 2022; likewise, Omicron BQ.1/BQ.1.1 and XBB.1.5 dominated between November 6, 2022, and January 21, 2023, and January 22 and April 1, 2023, respectively. The team also estimated RRs for unvaccinated controls.

The CDC retrieved study data, i.e., weekly counts of COVID-19–related deaths amongst unvaccinated individuals and bivalent booster recipients for September 18, 2022–April 1, 2023, from 20 U.S. jurisdictions. Note that the COVID-19 case surveillance data within the U.S. is linked to immunization registries and registration databases on a routine basis.

The CDC estimated average weekly mortality rates based on the date of sample collection during each period evaluated on this study stratified by vaccination status and time lapsed since receiving the bivalent vaccine’s booster dose, i.e., six months. 

They categorized rates for unvaccinated individuals by rates amongst bivalent booster dose recipients after detrending the linear variations in weekly mortality rates. They estimated the remaining 95% confidence intervals (CIs) from the variation in RRs observed. They conducted all analyses per CDC policy and federal law.

Observations

Amongst those≥65 years who received a bivalent COVID-19 vaccine booster or remained unvaccinated, there have been 8,161 COVID-19–related deaths across 20 U.S. jurisdictions between September 18, 2022, and April 1, 2023. 

The proportion of COVID-19-related deaths in 80-year-olds was 58% but inconsistent amongst vaccinated and unvaccinated individuals and across the three Omicron predominance periods. 

Nevertheless, mortality rates amongst unvaccinated individuals across all three periods were high. Quite the opposite, mortality rates amongst adults aged ≥65 peaked throughout the BQ.1/BQ.1.1 dominance period, i.e., December 2022. 

The CDC also reported time-stratified mortality rates amongst unvaccinated and vaccinated people two weeks to 2 months after receiving a bivalent booster vaccination.

They found that mortality RRs markedly reduced between the BA.5- and XBB.1.5-predominant period from 16.3 to eight.4, representing a moderate decline in vaccine effectiveness (VE) from 94% to 88%.

Alternatively, mortality RRs were comparable in individuals who received a bivalent vaccination two weeks to 2 months earlier or between three and 6 months before the BQ.1/BQ.1.1- the XBB.1.5-predominant periods, with RRs of 11.4 and 11.0 and eight.4 and seven.3, respectively.

Conclusions

To summarize, a bivalent COVID-19 booster vaccination provided substantial and sturdy protection against COVID-19–related death in adults aged ≥65 years.

More importantly, there was no corroboration of waning as much as six months post-vaccination, much like other studies evaluating VE against severe disease and death. Thus, CDC strongly recommends that each one people aged ≥6 months remain up up to now with updated COVID-19 vaccines, including a number of additional bivalent dose(s).

Additional vaccine doses are optional for immunocompromised and folks aged ≥65 years.

The SARS-CoV-2 spike protein within the bivalent vaccine is different; thus, CDC reported a slight decrease of 6% in immune evasion throughout the Omicron XBB.1.5 period in comparison with the Omicron BA.5 period.

Nonetheless, the study data are clinically relevant, especially regarding COVID-19 vaccine composition. Within the U.S., the COVID-19 public health emergency ended on May 11, 2023.

So, they discontinued routine monitoring of COVID-19 incidence, hospitalization, and death rates stratified by vaccine status. Yet, CDC continues to watch VE through well-controlled studies (e.g., the IVY networks).