Covid-19. Does vaccination prevent transmission and infection? What the studies say

Vaccination is very effective on severe forms and on the risk of hospitalizations. But does it completely prevent infection and transmission of the coronavirus? Numerous studies have been carried out on this subject all over the world. Here are their results.

This is a remark that often comes up in the mouths of people who are resistant to vaccination against the coronavirus : “we can transmit the virus even by being vaccinated ” , “being vaccinated does not prevent having the virus ” … But what is it really? Ouest France has compiled the results of several scientific studies on the subject.

It is rare, but it is possible to be infected with the coronavirus despite a vaccination

Regarding coronavirus infection, all studies show that vaccinated people have a much lower risk of developing the disease than unvaccinated people.

According to the Heroes-Recover study , funded by the CDC, the United States’ leading agency for public health protection, the risk of infection is reduced by 91% in fully vaccinated people (that is, – say two weeks after the second dose) with the mRNA vaccines Pfizer-BioNTech and Moderna. A large Israeli study of 1.2 million people suggested 92% effectiveness in fighting an infection after two doses of Pfizer.

But these figures have been revised downwards with the Delta variant. According to a study in Singapore , the effectiveness of Pfizer against infection with this variant is 69%. Another study conducted in Israel cited 64% .

At the margin, since the efficacy is not 100%, it is therefore possible to be infected despite a complete vaccination. This is called a vaccine escape. But these cases remain rare.

According to a CDC study in the United States , 10,262 cases of infections were identified in 46 states after vaccination. Of the 101 million vaccinated during the period when the study was carried out (January 1 to April 30), this corresponds to only 0.01% of those vaccinated.

However, the rare people who are infected despite their vaccination tend to develop symptoms that are less severe and for a shorter period of time than those who have been vaccinated, according to the Heroes-Recover study , updated in June 2021.

Transmission also decreases thanks to vaccination

On transmission, many studies have also been carried out. “The first scientific data are starting to show that vaccination could also reduce the carriage of the virus and therefore its transmission to other people. It is encouraging but we still lack perspective, especially with the variants which are more transmissible ”, wrote for example the ARS of Bourgogne Franche-Comté in May 2021 .

According to a very recent study by the Institut Pasteur pre-published on June 28, 2021 , “unvaccinated people have 12 times more chance of transmitting the virus than vaccinated people” .

A study conducted on Israel and published in the journal The Lancet conducted over the first four months of the vaccination campaign explains that “the high efficacy of the Pfizer vaccine against infection suggests that the vaccine reduces transmission.”

In the United Kingdom, a study published in Nature and carried out on 365,000 households indicates that even after a single dose of Pfizer or AstraZeneca, the risk of transmission is “halved”. Also in the United Kingdom, another large study carried out on 57,000 patients from 24,000 households by the British health agency concludes that transmission within the same household is reduced by 40 to 50% after vaccination. with Pfizer or AstraZeneca.

But again, if the vaccination does reduce the risk of transmission, then transmission is possible for a person to be vaccinated in rare cases. This is why maintaining barrier gestures is important even for vaccinated people.

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