Many other countries are delaying second doses. Why is that? Are we doing the right thing or do we have something to learn from others abroad?
Two different doses of Pfizer and Moderna are administering their COVID-19 vaccines on a different schedule from many other countries, including the United Kingdom, United States, Germany and Canada. Many people in the United States receive their second dose on schedule, three or four weeks after the first doses of the Pfizer and Moderna vaccines, respectively.
COVID-19 vaccines are a valuable resource that should be used wisely. Two doses of COVID-19 vaccines distributed around the world have left us a secret. Here we explain why the United States was gone from the very beginning and now why the relocation is a mistake.
“Now shifting gears would be a mistake”
The Pfizer and Moderna mRNA vaccines were designed to be administered in two doses, several weeks apart: a master and a booster. It was a pleasant surprise to learn from clinical trials that the first dose provided significant protection against COVID-19, at least in the short term. Based on these data, many countries are delaying the second dose to spread the limited supply to as many people as possible (this is actually the strategy adopted by the UK). It’s easy to think we should do the same, and some American public health experts urged us to do the same.
If you only had two doses, would you think, would you give both to one of your parents or one dose to each? The simplicity of this anecdote hides very real risks to individuals and the wider American public.
First, the strategy of administering two FDA-approved doses of Pfizer and Moderna vaccines at three and four-week intervals, respectively, is unquestionably more protective. more than a single dose. This is because the second dose of these mRNA vaccines dramatically increases both the levels of antibodies that neutralize the virus in our blood and our T-cell responses, the arm of the immune system that predicts more robust immunity. Real-world evidence from Israel and the UK shows that the risks of hospitalization and death are much lower after two doses of Pfizer mRNA vaccine. The Biden-Harris administration has promised to pursue science, and in this case this is clear.
Moreover, delaying the second doses at this point will fix the wrong problem. With the FDA’s support for emergency use of the Johnson and Johnson vaccine and Merck’s support to expand its production, the supply of COVID-19 vaccines will increase significantly in the next two months. The Biden-Harris administration predicts that we will have enough resources to vaccinate the entire American population by the end of May. The bottleneck is quickly becoming the speed of vaccine delivery, not the number of available doses.
At a time when the new administration is trying to increase public confidence in all vaccines, a change in policy can now confuse the public. Many people may wonder why it is necessary to take a second dose, especially as the single dose Johnson and Johnson vaccine is currently being launched. Others might be angry with public health officials for only partially protecting themselves against the virus. A change in policy can damage vaccine management systems, just as the sites take their steps.
But one of the main reasons for sticking to science is that we do not know how a change in the vaccine dosage schedule could affect the spread of new mutant variants of the virus that have appeared in recent months.
Variants can arise for different reasons, but a problematic source is that the virus replicates in the presence of relatively low levels of neutralizing antibodies. In this environment, it adapts to survival and produces new variants that are better able to survive immunity caused by existing vaccines as well as immunity caused by natural infection with earlier strains of the virus. Some variants are more contagious, meaning they spread more easily from person to person. Others are more lethal and cause more serious illness.
All of this has implications for the vaccine schedule. At least two laboratory studies found that the B.1.351 and P.1 variants that were first detected in South Africa and Brazil, respectively, evade antibodies induced by a single dose of the Pfizer and Moderna vaccines, whereas the higher antibody levels present after two doses are much more likely to remain protective. In the short-term, if we delay second doses of these vaccines, we could be creating a window of time when our vaccine-primed immune systems protect us against the original, or ancestral strain, but not against some of the new variants. At a population level, there is also a risk of selecting for new variants, creating a much bigger long-term problem.
If we had chosen a dose delay strategy for variants, would we have to boost our immune responses with a third dose of vaccine to control the outbreak? Or does this mishap mean that we have to wait for the second generation vaccines developed by Pfizer and Moderna before we can stop the virus and regain our freedom? Nobody knows, so we shouldn’t take these unnecessary risks.
Deviation from scientific evidence rarely works well when faced with difficult decisions such as how best to allocate the national vaccine stock. The Biden-Harris administration has promised to pursue science, and in this case the science is clear. The current COVID-19 vaccine application program is evidence-based, and we are putting the right thing forward.