With the prevalence of the highly transmissible delta variant and the corresponding new wave of COVID-19 cases, there is growing interest in the potential use of booster doses for vaccinated populations.
A review of available data by an international group of scientists supports the conclusion that more lives would be saved by using the current limited supply of vaccines for people who are at appreciable risk of serious disease and do not yet have access to any COVID-19 vaccine.
The review, published in The Lancet, summarizes currently available evidence from randomized controlled trials and observational studies published in peer-reviewed journals and pre-print servers.
The authors note that vaccines remain highly effective against severe disease from all current viral variants, and while their effectiveness against transmission and mild infection has declined somewhat, it has not done so substantially. It is unvaccinated individuals who continue to be the major drivers of transmission and carry the greatest risk for severe disease.
“Strategies for use of COVID-19 boosters should not be based on simplistic arguments such as, ‘some is good; more is better.’ Reliable insights are needed about whether and when immunity has sufficiently waned or viral variants of concern have emerged that meaningfully compromise vaccine efficacy against severe disease, hospitalization and death,” said Thomas R. Fleming, a University of Washington School of Public Health professor of biostatistics and statistics and one of the review’s co-authors.
And boosters aren’t without risk.
“We are really impressed with the safety of existing COVID-19 vaccines but we don't know what the safety will be with continued boosting, and whether we would be taking our remaining shots on goal too readily and too rapidly,” said Fleming.
Finding ways to increase worldwide vaccination rates would hasten the end of the pandemic more than focusing on boosters, according to the review.
“This is a pandemic. We don't beat it by developing individual-level or even country-level strategies; we need strategies that optimize levels of protection worldwide. Regrettably much of the lower income parts of the world haven't yet hit vaccination rates of 10%,” said Fleming.
“Achieving health equity should be a priority in our thinking. Ethically and scientifically, we need to achieve wide-spread protection while reducing the emergence of viral variants of concern. The delta and gamma variants emerged from regions where vaccination rates were low. Scientists should pursue, and political leaders should implement, evidence-based strategies that not only enable us to increase our supply of vaccines established to be safe and effective, but also to ensure their use in a manner, worldwide, to maximize benefits against risks.”
- Deb Nelson, UW Biostatistics Communications