With the pandemic continuing to reach new heights, the debate has arisen among experts on how to obtain maximum protection as quickly as possible from the limited supply of COVID-19 vaccines currently available.
Suggestions raised so far include delaying the second dose of a two-dose regimen for perhaps three to four months, instead of distributing them at the planned intervals of three to four weeks evaluated in large clinical trials. With this change, more people can now receive their first dose, offeringsome protection. Another possibility is to simply cut the doses in half, which would immediately double the number of people who can be vaccinated now. And regulators in the UK introduced the idea of mixing regimes – with some people getting their first dose of a vaccine from one manufacturer and then receiving a second dose of the vaccine from a different manufacturer based on availability at the moment.
The evidence supporting these suggested adjustments to the vaccine launch is, at best, unstable. But some experts argue that the terrible state of the pandemic justifies a new, perhaps more risky, approach.
Viral crush
“[A]s Mike Tyson said the famous phrase: ‘Everyone has a plan to get punched in the mouth’ ”, Robert Wachter, head of the medical department at the University of California, San Francisco, and Ashish Jha, dean of Brown University School of Public Health, wrote in an opinion article published on Sunday in The Washington Post. In the opinion article, the duo presents an argument for delaying second doses, writing: “When it comes to COVID-19, we are getting punched in the mouth repeatedly. It’s time to change the plan. “
Wachter and Jha note that the researchers did not analyze what happens if a person takes just one dose of a two-dose vaccine schedule. In the USA, the Food and Drug Administration has authorized the use of Moderna’s COVID-19 mRNA vaccine and another mRNA vaccine made by Pfizer and BioNTech. In large Phase III clinical trials, both vaccines showed about 95 percent effectiveness in protecting against COVID-19 – but only after two doses administered 28 days (Modern) or 21 days (Pfizer / BioNTech) in between. It is not clear how effective the vaccine is after just one dose and how long this protection can last.
The single-dose strategy “has not been studied, so we don’t know if and when immunity from the first injection starts to decrease,” wrote Jha and Wachter. “But”, they continue, “the data from Moderna, for example, is comforting. It shows a robust immune response four weeks after the first injection, and most experts believe that immunity is somehow unlikely to collapse in week eight or even week 12 after a single injection. “
Risks and unknowns
That thought seemed enough to influence health officials in the UK. Last week, they announced that they would allow the interval between the first and the second injection to be up to 12 weeks. They also opened up the possibility that people could receive the first and second doses of the vaccine from different manufacturers – for example, a person could receive a first dose of the Pfizer / BioNTech vaccine followed by a dose of the AstraZeneca / COVID-19 vaccine / Oxford University. (The AstraZeneca vaccine is another two-dose vaccine that was approved in the UK last week. American officials expect the FDA to grant emergency authorization in the coming months.)
But other experts are still strongly opposed to the idea of postponing a second dose. Although immune responses may not plummet dramatically in a few months, they will decrease over time. And, as researchers still do not know what level of immune response is needed to prevent infections and diseases, it is not possible to say that a single dose will be enough to prevent people from being infected or sick.
Furthermore, decreased immune responses after a dose can make the coronavirus more dangerous. Some experts have noted that having the virus circulating wildly mixes with many people with weak Immune responses can create the perfect selective pressure for the virus to adapt to escape those immune responses. Coronaviruses mutate naturally over time and several variants – including those in the UK and South Africa – have already emerged and appear to spread more easily among people. So far, these variants do not appear to generate more serious or deadly diseases. And they are not believed to prevent the immune responses of natural infections or authorized vaccines. But partially vaccinating large numbers of people can lead to these nightmare scenarios, some experts fear.
Following science
With the uncertainties and risks, many experts are strongly opposed to tampering with the vaccine plan. This includes the leading infectious disease specialist, Anthony Fauci. Last Friday, Fauci criticized the idea of the US following the UK’s example by allowing a second postponed dose. “I would not be in favor of that,” said Fauci in an interview with CNN.
“The fact is, we want to follow what science tells us and the data we have for both [vaccines] indicate that you give a prime, followed by a boost in 21 days with Pfizer and 28 days with Moderna, ”said Fauci. “And now, this is how we are going, and that is the decision that is made.”
Moncef Slaoui, chief scientist of the US government’s Operation Warp Speed, echoed Fauci’s opposition to postponing second doses in an interview on Sunday with CBS ‘ Face the Nation.
“We have always said that these vaccines will be developed based on science and all decisions will be made transparently based on data,” said Slaoui. “Changing the decisions made, the choices made, which was to give two doses of the vaccine – the second dose gives you an immune response ten times greater than the first dose – without any data that I think I would not be responsible for.”
However, interestingly, Slaoui offered yet another alternative to maximize the vaccine’s implementation:
“Here is the alternative. We know that, for the Modern vaccine, giving half the dose to people between 18 and 55 years old – two doses, half the dose, which means exactly reaching the goal of immunizing twice the number of people with the doses we have – we know that it induces an immune response identical to the dose of one hundred micrograms and, therefore, we are discussing with Moderna and the FDA.
“Of course, ultimately, it will be an FDA decision,” said Slaoui. But, he added, “I think it is a more responsible approach that will be based on facts and data.”