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Covid-19: vaccinated then tested positive, how is this possible?


A nurse in #San #Diego (#California), symptomatic and tested positive a week after receiving a first dose of the #Covid-19 vaccine. 66 residents and 20 employees of an nursing home in #Canada, infected a few days after vaccination. These two episodes, recounted respectively this #Tuesday by ABC #News and this #Wednesday by the #Canadian press, have sparked many comments on social networks. #However, there is nothing impossible or alarming about them. #Explanations.

The nurse in the #United #States and the residents or employees of the #Canadian nursing home all received a first dose of the #Pfizer-BioNTech vaccine. #But vaccinated people are not immediately protected against the onset of symptoms of the disease.

A delay before protection

#First of all, “until the vaccination allows us to have the benefits in terms of protection, there is a delay of about two weeks for the rise of antibodies,” #Jacques #Girard told #Radio #Canada, medical assistant to the director of public health in #Quebec. “#It is quite classic that the effectiveness of the vaccination does not intervene immediately when we have injected the product, there is no surprise to that”, agrees with the #Parisian infectious disease specialist #Nathan #Peiffer- #Smadja, who works at the #Bichat hospital.

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#At #Reuters, the #Pfizer group also insisted that “the vaccine offers some protection against #Covid-19 within about 10 days of the first dose””. #This protection relates to the appearance of symptoms, not necessarily the infection itself. “The vaccine prevents the disease from being generated. #It is likely that it also limits the risk of infection, even if we do not yet have definitive proof, ”explains #Nathan #Peiffer-Smadja.

#Ten days before seeing the first benefits of the product, it is also the delay put forward by the #Food and #Drug #Administration (FDA), the #American drug agency which authorized its marketing.

#Two doses three weeks apart

#But above all, for the vaccine to be as effective as possible, two doses must be administered to patients three weeks apart. #Its efficacy “is considerably enhanced after the second dose, which confirms the need for a series of two-dose vaccines,” #Pfizer insisted. “#We think that the first dose gives you about 50%, and you need this second dose to reach 95%”, added on ABC the infectious disease specialist #Christian #Ramers.

#But even with two doses, the vaccine would not be effective in preventing all patients from developing symptoms. The 95% efficacy announced by #Pfizer is already a very good performance, which has been praised by many doctors around the world, but it does not guarantee absolute protection for all.

#Newsletter #Morning essentials

A tour of the news to start the day

VIDEO. #BioNTech: “#We can provide a new vaccine in six weeks”, in the event of a mutation of #Covid-19

#Finally, in the two examples we are talking about, it is also possible that people were infected before being vaccinated. The incubation period between contamination and the onset of symptoms is on average five days, but it can last up to twelve days. #As ABC sums it up, such a scenario “was not unexpected”.





[ source link ]
https://www.leparisien.fr/societe/covid-19-vaccines-puis-testes-positifs-comment-est-ce-possible-31-12-2020-8416813.php

##Covid19 #vaccinated #tested #positive

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