September 14. The United States and many other countries around the world are still debating the rollout of an additional dose, or “booster” shot, of the Covid-19 vaccine. On Friday the US Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee will meet to discuss Pfizer’s application to administer a third dose of its Covid-19 vaccine to people ages 16 and older. Though a recent Lancet article advises caution in administering boosters before we have the evidence to fully support that the immunological benefits outweigh any risks.
What is yet to be understood fully, is whether three doses alone will be enough. Science is not static, and our determination of what is needed to protect us against SARS-CoV-2 will change as our understanding of the virus evolves. But if you look at what we know today about the virus and our vaccine-induced and natural immunity, the likelihood is that we will need additional shots.
Coronaviruses, like influenza viruses, are masters at evading the immune system. Their ecological niche is in long-lived animals with competent immune systems. These animals typically have been infected many times over by the virus’ own predecessors. Think of the annual waves of influenza infections and you will have a pretty clear picture of what could potentially lie in store for us with SARS-CoV-2.
A July 31 study found that protection from Covid had faded in proportion to the length of time since vaccination. According to the authors of the study, “Individuals who were vaccinated in January 2021 had a 2.26-fold increased risk for breakthrough infection compared to individuals who were vaccinated in April 2021.” What this study told us was that the levels of vaccine-induced neutralizing antibodies mattered, and when antibodies drop, infections go on the rise.