Yearly COVID Boosters for Older Adults May Produce Largest Gains

September 30, 2022
By Nellie Bristol

Under COVID-19’s current course, yearly vaccination focused on high risk populations is most likely to prevent the most hospitalizations and deaths and prove more cost effective than aiming for regular full population immunization, Professor Azra Ghani of Imperial College said September 29. Speaking at a webinar hosted by the Andean Health Organization, Ghani cited mathematical modeling data showing the largest decreases in hospitalizations and deaths derived from providing annual boosters to those over 75. Additional benefit was seen in annual boosters for those over 60. While more frequent vaccination was considered, Ghani said, “We don’t see so much benefit in moving to six monthly vaccines,” she said. “That’s partly because we don’t see too much of a drop off in vaccine efficacy over the first year of boosting, but clearly the yearly boosting is important.”

While its trajectory remains uncertain, if current epidemiology holds, Ghani described COVID-19 as creating gradually smaller waves of infection until it settles into an endemic state. As it does, countries will need to establish long term vaccination protocols. “We’re likely to have high levels of the virus circulating worldwide in the years to come,” she noted. “The question that arises is what strategy should countries pursue? Should we be doing yearly boosts of all age groups, or should we just be focusing on priority groups at highest risk?”

While Ghani’s data showed wider impact on transmission through all-age vaccination, the largest drops in death and hospitalizations occurred by focusing on older adults and others at highest risk. Efficiency, which Ghani said is closely related to cost effectiveness, followed a similar pattern. The biggest efficiency gains occurred through regular vaccination over a three dose only strategy with targeting of older ages more efficient than all age efforts and yearly vaccination more efficient than six monthly. In areas with limited vaccinate supply, she said, targeting the highest risk is substantially more efficient.

Ghani, a professor of epidemiology, was co-author of a Lancet Infectious Diseases article published in June this year that calculated that vaccinations prevented 14.4 million COVID-19 related deaths in 185 countries between December 8, 2020 and December 8, 2021. In low income countries, it noted, an addition 45% of deaths could have been averted if the 20% vaccination coverage target set by COVAX had been met by each country and an additional 111% of deaths could have been averted had the 40% target set by the World Health Organization been met by each country by the end of 2021.

Data supporting the importance of targeting high risk populations for vaccination was part of a set of recommendations reviewed for the webinar by Duke University Senior Program Manager Ernesto Ortiz, MD. Ortiz highlighted a report published September 19 by COVID GAP and the COVID Collaborative that emphasizes the importance of fully protecting older adults, the immunocompromised, and those with preexisting conditions as well as health workers with full vaccination including boosters and access to test-and-treat options. It further calls out the need for data disaggregated by age, gender, health status, and geography, to identify who is most at risk, where they are located, and whether they are being reached effectively.

Ongoing vaccination of adults will require expanding national immunization programs, which often are focused on essential immunizations for children. Developing strategies to incorporate COVID specific services into national immunization and primary care settings is critical not only to long term COVID vaccination, but also will create essential platforms for providing broad access to vaccinations for future disease outbreaks.