Back in July 2020, in an interview with CBS Evening News’ Norah O’Donnell, Microsoft co-founder and billionaire philanthropist Bill Gates said that it is likely that an effective coronavirus vaccine will require “multiple doses” to protect American people from the coronavirus – A disease that has a lower mortality rate in children than the seasonal flu.
The only way to end the pandemic for good is to offer a vaccine to almost all of the planet’s 7 billion inhabitants, Bill Gates said.
Finding the right vaccines won’t end the challenge. Gates says it’ll be tricky to ramp up production, particularly since we don’t yet know which candidates will work.
Multiple vaccine doses could be necessary to protect from coronavirus, Bill Gates says https://t.co/dZJa2UVJje
— CBS News (@CBSNews) July 22, 2020
“What we can do now is build different kinds of vaccine factories to prepare,” he says. “Each vaccine type requires a different kind of factory. We need to be ready with facilities that can make each type, so that we can start manufacturing the final vaccine (or vaccines) as soon as we can. This will cost billions of dollars. Governments need to quickly find a mechanism for making the funding for this available.” Gates said.
Many of the newly developed COVID-19 vaccines, such as the ones from Pfizer/BioNTech and Moderna, require two doses, at least three weeks apart. Vaccines that require multiple doses weeks, months, or even years apart are not unprecedented. The Hepatitis B shot, for example, is required for newborns with a second shot required one to two months later.
According to the CDC, there are a few reasons for this. First of all, a single dose may not be enough to provide the necessary immunity to protect one from getting the illness. Multiple doses may increase efficacy and provide much greater immunity. This was the case with the Pfizer clinical trials, in which the data showed that one dose was 52% effective whereas two doses were 95% effective.
Infectious disease physician Carlos Malvestutto says, “The first dose primes the immune system while the second dose induces a vigorous immune response…” Essentially, a second dose provides more antibodies (also called immunoglobulins), which are “proteins produced by the immune system” in order to fight against foreign substances (antigens).
The answer to the question: “Why do some vaccines require multiple doses?” is largely based on the mechanism behind vaccines. Traditional vaccines contain either weak or inactivated versions of the pathogen (which can be a virus or bacteria), provoking an immune response, allowing the immune system to effectively deal with the pathogen if it enters the body again. It is often the inactivated vaccines that need multiple doses because they are not as close to the actual pathogen in comparison to vaccines that use weak, live versions of the pathogen.