Can someone who has received the covid vaccine pass the virus on?

Experts doubt whether the Pfizer vaccine can stop new infections

The Pfizer vaccine being administered in care homes is designed to prevent people from getting sick if they get covid. However, preventing the disease does not necessarily stop the transmission of the virus. It appears that the vaccines will be able to minimize the risk of severe covid in 95% of cases and therefore reduce hospital admissions and deaths caused by the coronavirus. Nevertheless, their role in group protection remains unclear: can a vaccinated person become infected and potentially transmit the virus to other individuals?

Three experts consulted by the ARA agree that there is not enough evidence to say that these vaccines will stop the spread. With the information available, they say, they will avoid the symptoms of the disease, both in its mild and severe form, but warn that it is still too early to conclude that vaccinees could avoid infection and not spread it to others, as is already the case with other diseases such as diphtheria: vaccinated people can get the virus without suffering the disease, but they can transmit it to someone who is not vaccinated.

Lack of refrigerators to move vaccines makes it impossible to maintain the planned herd immunity rate

"Preventing infection and preventing disease are different things", Carlos Rodrigo, vaccinologist and clinical director of pediatrics at the Germans Trias y Pujol Hospital, summarizes. The expert rules out, for now, that blocking the infection - which would be the only way to avoid transmission - is a result of the Pfizer vaccine: "It doesn't seem that they would be able to induce a group protection response". Carlota Dobaño, director of the immunology research group at the Institute for Global Health in Barcelona (ISGlobal) (a centre promoted by the La Caixa Foundation), agrees with this statement.

Firebreak effect

"Many of the vaccines that have a protective effect against the disease also act as a transmission firewall, since not developing the virus is associated with a lower viral load and a lower capacity for transmission, but for now we cannot say that in this case it will surely be fulfilled", the immunologist admits. Rodrigo reminds us that the aim of a vaccine is to protect the person who gets it. "It's when the vast majority of the population is vaccinated that the group or community is indirectly protected", he says.

According to Pfizer studies, the vaccine's efficacy in trials is of 95% and this means that virtually everyone who gets it is protected; a "very high" threshold, according to experts. "If afterwards the effectiveness drops a little in the population, many people will still be protected", the director of microbiology of the Vall d'Hebron, Tomàs Pumarola, explains. The flu vaccine, for example, works only among half of those vaccinated and, despite being able to catch the virus, "there are usually no serious cases because the vaccine always gives them some protection".

Josefa Pérez, the first Catalan person to receive the covid-19 vaccine

The experts consulted are confident that virtually none of those vaccinated will develop the disease if infected. "We hope that most people who have been vaccinated will be cured asymptomatically" Dobaño acknowledges, and notes that this will reduce the number of hospitalizations. "Avoiding the disease is the first goal we can achieve and the most important aspect in terms of public health, since it will prevent the health system from collapsing", he explains. That is why the vaccination campaign prioritizes older people. "It will be considered a success if the most fragile are protected" Pumarola says. 

Two doses

The Pfizer vaccine consists of two doses given 21 days apart, and maximum protection is obtained one or two weeks after the second dose is given. In the process, however, a person can be exposed to the virus and become infected. "We think the first dose might be protective enough to prevent serious conditions, but we don't know", Pumarola said. Dobaño agrees: "It would be a short, low-intensity protection."In addition, the symptoms could be confused with those of the infection or with side effects", Rodrigo warns.

Vaccination is not a synonym of relaxation. As long as there is not a vaccination rate of 70 to 90 per cent of the population, which is known as herd immunity, the population will have to wear a face mask, respect physical distance, and exercise extreme hand hygiene, whether they have received the vaccine or not.

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