Science unclear around fourth COVID-19 shot

Several countries—including Israel, Denmark, Hungary, and Chile—have authorized second booster shots of COVID-19 vaccine, but concerns have recently been raised about whether this is a useful approach.

The findings from a recent study conducted in Israel suggest that a fourth dose of the COVID-19 vaccine does not offer significant protection from the Omicron variant, according to a January 18, 2022 Deutsche Welle article. In addition, the World Health Organization has suggested that blanket booster policies will increase inequity and prolong the pandemic by diverting vaccines toward countries with already-high levels of coverage, resulting in more opportunities for the virus to spread and mutate in less vaccinated countries.

Sarah Fortune, John LaPorte Given Professor of Immunology and Infectious Diseases and chair of the Department of Infectious Diseases at Harvard T.H. Chan School of Public Health, addressed another issue raised in the Deutsche Welle article— that frequent boosters might fatigue people’s immune systems. She explained that when immune systems repeatedly see antigens such as those provided by vaccines, T cell “exhaustion” could result. However, she said that the science is more complicated in the case of COVID-19.

“T cells become dysfunctional when they repeatedly see antigen in certain contexts—and the best studied of that biology are settings like HIV or cancer where the antigen is there all the time, not just repeated vaccination,” she said. At this stage, she said, T cell exhaustion is a concern that researchers should watch out for, but not one that should be guiding policy.

Read the Deutsche Welle article: COVID: Do multiple boosters ‘exhaust’ our immune response?