Main risks associated with postponing the second dose of COVID-19 vaccine, according to Anthony Fauci

Given the shortage of inoculants, health authorities in UK and Canada have decided to postpone application of second dose of COVID-19 vaccine to reach more population at higher risk complications with the first dose.

In the In the United States, more than 40% of adults have received at least one dose of the vaccine, but cases have increased for four consecutive weeks. “We know that These increases are due, in part, to more highly transmissible variants, which we are monitoring very closely, ”he said. Rochelle Walensky, director of the Centers for Disaster Control and Prevention (CDC), during a briefing Monday at the White House.

His warning underscored the concern of Anthony Fauci, the leading infectious disease expert for the United States government, who Americans must receive the two doses of Pfizer and Moderna vaccines on time, even if the extension of these deadlines allowed the United Kingdom to accelerate ahead of the United States in the race for vaccination.

For the specialist, delaying a second dose of the vaccine could put people in a “soft zone” of risk for contracting a more infectious variant of the coronavirus. To the doctor Fauci you are concerned that people who have not had the ‘full effect’ of two doses of the vaccine may be dangerously vulnerable to infection with variants that weaken the effects of antibodies.

In the United Kingdom, the second dose of vaccines manufactured by Pfizer O AstraZeneca it can be delayed up to 12 weeks. The strategy was controversial when it was introduced there, but it has helped the UK to ensure that nearly half of its population has some level of protection with one or more doses of the vaccine.

At this moment, Fauci he rejected and even criticized the UK for employing the unproven strategy (although he later backed down on his harsh words). But Monday he said there was no “right or wrong” strategy for delaying doses. “There are different approaches and opinions,” he acknowledged.

“We have been concerned, and we are still concerned, that when looking at the level of protection after a dose, we can say that it is 80%, but it’s something like a slight 80%, because the level, for example, of neutralizing antibodies against the coronavirus, when you leave it in a single dose, the question is, how long does it last? “, asked the expert.

Research published last month showed that the risk of contracting COVID-19 after a first dose of Pfizer or Moderna vaccines has been reduced by approximately 80% within two weeks of this first injection. But a second dose was given to these people a week or two later, depending on whether or not they had received the vaccine. Pfizer, who has a dosing schedule with an interval of three weeks, or that of Modern, which should be administered four weeks later.

It is not known how well people will be protected with a dose after this second week. And with the variants in circulation, every piece of protection counts. Two doses of either vaccine continue to protect against vaccine avoidance variants from Brazil and South Africa. But the antibodies generated by these vaccines are two to six times less effective at binding to the spike protein that allows the coronavirus to enter human cells.

So, in Dr. Fauci’s opinion, It may not be worth the risk of leaving more people on a single first dose for longer. Neither variant is common in the United States, so the chances of Americans finding them are slim.

Until now, the South African variant and Brazilian variant represent each less than 0.05% of COVID-19 cases in the United States, according to the follow-up of Outbreak.info. Yet they are significantly more infectious than the “wild type” virus, and experts fear they may become more prevalent.

Recently, a scientific study conducted by researchers in Canada has now warned that postponing the second dose may carry risks of further increase in COVID-19 outbreaks in the future. The study was published in the journal Science and was conducted by researchers from Princeton, Harvard and Columbia Universities and the National Institutes of Health in the United States, the Universities of Montreal and Mc Gill in Canada, the University of Oxford and the Wellcome Trust in the UK. Uni, and the University of Sydney of Australia.

Although the work has mainly focused on the Pfizer / BioNTech, Moderna and Oxford / AstraZeneca vaccines, the researchers specified that the results “can be generalized on all platforms”. “Several countries, including the UK and Canada, have said they will delay second doses of COVID-19 vaccines in response to supply shortages, but also in an attempt to rapidly increase the number of people vaccinated,” has explained Chad Saad-Roy, who works in the departments of Ecology and Evolutionary Biology (ESB) and Quantitative and Computational Biology at the Lewis-Sigler Institute in Princeton and was the lead author of the study.

“The original clinical trials of the vaccines, as well as the subsequent epidemiology, are quite optimistic about the effectiveness of the first dose. However, we still do not know how long the long-term protection and duration of single-dose immunity will persist (or the full two-dose cycle or a natural infection, really), ”he added. Saad-Roy.

The study found that one dose may not be enough. He identified that single-dose strategies can, as expected, reduce the number of cases in the short term by immunizing more people more quickly. However, if people’s immune responses after a dose are less robust, subsequent outbreaks may be larger.

Another important finding associated with imperfect immune responses that’s the potential for viral immune breakout, the researchers warned. To begin to address this complex question, the authors adapted an earlier model of viral immune evasion, developed by co-authors. Bryan Grenfell, Oliver G. Pybus and Edward C. Holmes, with other colleagues who were not involved in the work in progress.

“At least one variant has already emerged which can be adapted to partially evade immunity.”noted Dr. Holmes. “The simple theory emphasizes that the evolution and transmission of variants by infected hosts with intermediate levels of immunity can be important. Therefore, the strength and duration of immunity, and in particular their effect on retransmission, are key parameters to be determined, ”he added. Grenfell.

An intuitive finding that the document highlights is that very low vaccine delivery rates may be associated with a higher number of cases and eventually to a higher adaptation potential of the virus. “This strongly emphasizes the importance of equitable distribution of vaccines globally, as leakage of the immune system in one place spreads rapidly “, Explain Jessica Metcalf, co-author of the book, researching at the Princeton School of Public and International Affairs.

In the study published in Science, the scientists wrote: “When vaccine distribution is delayed and vaccination rates are low, our results emphasize the negative epidemiological and evolutionary consequences that may result. In particular, since ethese consequences (for example, the evolution of new variants) could arise as global issues, this underlines the urgent need for global equity in the distribution and administration of the vaccine ”.

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