One year after the start of the covid pandemic, what are our weapons to fight the virus? Several vaccines have been developed in record time. And if their effectiveness is now demonstrated, many questions still remain unanswered, as raised in an article entitled “Covid-19 in 2021 – a lingering uncertainty“published on March 4 in the JAMA.

The two authors, specialists in infectious diseases at the American universities of Emory and Michigan, take stock of the knowledge acquired on vaccines and the gray areas that remain to be clarified.

To date, two messenger RNA vaccines (Pfizer and Moderna) and one vector vaccine (Johnson & Johnson) have been authorized in the United States. Europe has not yet authorized the Johnson & Johnson vaccine but also has the AstraZeneca vaccine, also a vector vaccine.

Also read: INFOGRAPHIC – We explain how the different types of vaccines work

All these vaccines “have been shown to be safe and very effective in preventing severe cases of covid and death “ note the specialists. Who to distribute them to? For the authors, people eligible for vaccination “should receive the available vaccine“at that moment, whatever it is. But when the doses are less limited, mRNA vaccines should be reserved for people who are at higher risk of severe forms, such as the elderly or the immunocompromised.

  • Prevent infection or transmission?

Vaccines are effective, but do they block the very transmission of the virus or the onset of symptoms? The best way to fight the pandemic would be to block both infection and transmission, but no evidence is available at this time. The next few months should allow us to find out more.

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Read also: Covid: “good reasons to hope” that the vaccine also prevents the transmission of the virus

  • Are vaccines effective against variants?

The answer to this question is uncertain. The Pfizer and Moderna vaccines appear to be effective against the British variant. But too little data is available to date on other vaccines and other variants, such as the South African or Brazilian variant.

  • Once vaccinated, what behavior to adopt?

Who says vaccinated does not say unmasked! The respect of barrier gestures must continue, because there is no data for the moment to know whether a vaccinated person can transmit the virus or not.

In the United States, health authorities indicate that 14 days after receiving the second dose of a covid vaccine and for a period of three months, vaccines no longer need to isolate themselves if they are in contact. Not in France, where the government confirms that we must continue to isolate ourselves in case of contact with a positive person.

  • How long are we immunized?

It is not known exactly how long the immunity will last after vaccination.“and”vaccine boosters may be needed given growing evidence of virus evolution and new variants“acknowledge the authors of the study.

But what scientists are sure of is that vaccines work at two levels of the immune system: at the level of antibody production and at the level of activation of memory lymphocytes, whose lifespan – and therefore l effectiveness – in the body can be very long.

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  • Can the vaccines be mixed?

The first dose with one vaccine, the second dose with another, is it possible? Currently not. No data allows to know to date whether such a mixture would be effective but several studies are underway to examine the effectiveness of the combinations which could in theory “strengthen protection against covid“note the authors of the publication.

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Note: the question will not arise for the Johnson & Johnson vaccine, which requires only one dose.

  • Can we receive a single dose?

Pfizer, Moderna or AstraZeneca vaccines are administered in two doses. In France, the Haute Autorité de Santé recommends that people who have already had covid receive only one dose of these vaccines. The disease would indeed be enough to trigger an immune memory and the first dose would then act as a reminder.

This is not the case in the United States, where health authorities fear that a single dose will offer only partial protection, which would contribute to the emergence of new variants, recalls the article in JAMA.

  • Will the covid become seasonal?

For the two specialists, “it is likely that in the coming months, covid will be phased out from some countries but will continue to spread to others “.

And in the longer term? “SARS-CoV-2 could become endemic“i.e. exist constantly, like HIV or the herpes virus for example,”or seasonal, with outbreaks during the winter monthslike the flu virus. Here again, only time will tell.