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The United Kingdom and unknown aspects of the vaccines

In a historic decision, the United Kingdom became the 1st country to authorize use of the Pfizer BioNtech anti COVID-19 vaccine in the light of trial results. This authorization was granted at an impressive speed, on the 2nd December 2020. Only China and Russia had already authorized their vaccines, but without waiting for the conclusions of clinical trials. Decisions by the Americans and the European Union are expected in the coming weeks. The Pfizer vaccine proved to be effective in preventing illness in 95% of the 43,000 participants in trials. However, numerous questions still remain concerning the vaccine, and the same is true of the two other vaccines that have been widely tested: the Moderna and AstraZeneca vaccines.

What are the differences between these vaccines?

The Pfizer and Moderna vaccines are based on RNA technology: a molecule of RNA is encapsulated in a lipid particle which facilitates its entry into the cell. This RNA molecule works as a matrix to enable the fabrication of a viral protein, thanks to the cellular machinery (the spike protein). As for the AstraZeneca vaccine, it is based on a viral vector: a DNA molecule is transported into the cell using a harmless virus.

These differences can be represented thus:

Because of the limitations of current data, it is difficult to compare the advantages and disadvantages of these vaccines, which may turn out to be more effective in certain sectors of the population than in others. There are also differences in logistics and cost (for example, the Pfizer vaccine must be kept at -70°C, while the AstraZeneca vaccine is less expensive). 

Will the vaccine prevent transmission of the virus?

These vaccines enable us to avoid illness. But none so far has been shown to be effective in preventing infection of an individual by the virus or in reducing its transmission in the population. Someone who is vaccinated can therefore be infected but remain asymptomatic, while transmitting the virus to other, possibly vulnerable, people.

How long will the immunity provided by the vaccine last?

There is no quick way of determining the length of long-term immunity. Studies seem to indicate that the immune system develops memory-cells following Sars-CoV-2 infection. However, cases of reinfection have already appeared despite the development of specific antibodies. In addition, the prevalence of such cases of reinfection is not known. It’s therefore important that health authorities pay careful attention to this question of long-term immunity.

Are the vaccines effective on groups of the population such as children or elderly people?

Despite the clinical trials, there are few reliable statistics on different groups of people vaccinated (obese people, the elderly…). Preliminary data simply indicates that the vaccines seem to protect individuals aged over 65. No data exists concerning the vaccination of children or pregnant women.

Can the virus evolve and bypass the immunity provided by the vaccine?

Certain viruses such as the flu rapidly start to acquire numerous mutations in their genome. This is not the case for the Sars-CoV-2 virus, whose genome appears relatively stable. On the other hand, a massive vaccination programme and growing herd immunity may bring pressure on the selection process and accelerate the appearance of mutations. It’s therefore very important to continue to watch out for mutations and thereby work on evolving the next generations of the vaccine.

Numerous questions still exist regarding the vaccines, in part because clinical trials took place over a few months rather than the usual 2 years. But careful monitoring has always been carried out even after commercialization of vaccines in the past, which would seem to be particularly important in the case of  the new anti-COVID-19 vaccines.

[1] Weekly letter november 16-22 2020

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