Covid-19: Delaying the second dose of vaccines appears to be a good strategy for Coronavirus

Since the start of vaccination and facing vaccine shortages and logistical challenges, many states, including Canada and the United Kingdom, have decided to give a first dose to as many people as possible as quickly as possible. From the second dose.

The goal was to quickly vaccinate as many people as possible.

The National Advisory Committee on Immunization said on Tuesday that it will make a formal recommendation, within a week or two, about the interval between the two doses for the elderly and those with immunosuppressed populations.

British example

Thus, delaying the second dose allowed more Britons to be vaccinated more quickly.

Since vaccination began in the UK, more than 50% of the adult population has received at least one dose of the AstraZeneca-Oxford or Pfizer-BioNTech vaccine.

The result is startling: the UK, which recorded an average of 60,000 new cases of COVID-19 per day in January, now has around 5,400 daily cases.

Judging by early clinical trials of vaccines and subsequent epidemiological data, the first dose is very effective. But at this point, it is not known how long the immunity that this first dose (or even the two doses or natural infections, for that matter) will remain effective.Shady Saad Roy of Princeton University explains in a statement.

The British success is even more appealing considering that nearly 100% of new infections in the country are caused by the popular British variant, which is much more transmissible and lethal.

So it is clear that vaccination is effective against this variant.

A model for projecting the future

To make successful predictions about the incidence of COVID-19 and the level of immunity of the population, researchers created simple models of different vaccine regimens and different hypotheses about the immune response.

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Due to the immune and epidemiological uncertainties surrounding these findings, we should definitely use simple models to project ourselves into the future.Caroline Wagner, associate professor at McGill University and lead author of the article explains.

One dose is not enough

As the researchers expected, their models show this The first dose will reduce the number of cases in the short term by vaccinating a larger population more quickly. However, if that first dose triggers a less powerful immune response, the subsequent waves may strike harder..

However, as our vaccine capacity increases, we may speed up vaccination or move closer to the recommended two-dose schedule, so these long-term epidemiological effects are likely to be less clear.Professor Wagner adds.

Weaker immune response?

Another possible consequence of a partial immune reaction is that the virus escapes the immune attack. The authors of this work have published in the journal Science (A new window) (In English) Model Conditioning The dynamics of life Simple immune evasion.

Their theory is that In a partially immune subject, virus can develop in the presence of moderate selection pressure and sufficient viral transmission. The authors studied this possibility, along with a series of other scenarios, including more optimistic scenarios, where the potential for adaptation is minimal in a host whose immunity declines after one or two doses of the vaccine.

Indeed, at least one type that can partially evade the immune system is in circulation, Confirms Edward Holmes of the University of Sydney in Australia.

The simple theory teaches us that a host showing moderate immunity can play an important role in the evolution and transmission of variants. That is why the strength and duration of immunity, and especially its effect on retransmission, are factors of prime importance here.Fellow Brian Greenville of Princeton University adds.

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Additionally, the researchers present an intuitive result: Very low rates of vaccine administration may be associated with a greater number of cases and, sooner or later, a higher likelihood of viral adaptation.

This highlights the importance of equitable distribution of vaccines globally, as immune leakage spreads in one place rapidly.Jessica Metcalfe, of the Princeton School of Public and International Affairs, explains.

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