Coronavirus: Why the covid vaccine does not prevent the transmission of the virus | Science


Vaccination against covid-19 in the province of Huelva.
Vaccination against covid-19 in the province of Huelva.JUNTA DE ANDALUCÍA (Europa Press)

Vaccines against covid prevent hospitalization and death in more than 90% of cases, but not contagion and transmission of the virus. That is why it is expected that there are vaccinated people who become infected with SARS-CoV-2 and can transmit it to other people, even if they have also been immunized.

Do vaccines prevent infection?

Yes, although it is not known how much. This is a problem that could not be well studied in the initial clinical trials on the effectiveness of vaccines. We had to wait for the implementation of the injections in the real world. A study of this type published in April this year and in which almost 4,000 doctors and health workers in the United States participated shows that messenger RNA vaccines – those from Pfizer and Moderna – prevent infection by 90%. Other studies carried out when the delta variant, more contagious, was the majority, saw a decrease in effectiveness against infection, which dropped to 51% in the case of Pfizer and to 73% with Moderna. In Spain, protection against infection ranges between 70% and 90%, according to the latest report on the subject from the Ministry of Health. The study highlights that “a high global effectiveness is maintained even after several months of vaccination and after the arrival and expansion of the delta variant, at the end of June”.

Can you suffer covid while being vaccinated?

The efficacy of vaccines is not 100%, so there can always be a case of this type. In any case, the vast majority of seriously ill covid who are registering in recent months were not vaccinated. Having received the immunization multiplies by 10 or more the protection against the covid.

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What percentage of those vaccinated get seriously ill?

It is very difficult to know and it depends on the situation in each country. In any case, it is a very low proportion. In the United States, the rate of infections among those vaccinated is between 0.01% and 0.54%, according to a tally by the Kaiser Foundation published in late July. The hospitalization or death rate is 0.06% and 0.01%, respectively. This incidence is similar to that registered in Israel (0.02%).

What is happening in Spain?

The Ministry of Health does not provide data on how many cases of infection there are among those vaccinated, although this newspaper has repeatedly claimed them. What is known is that most of the severe cases were not vaccinated. The effectiveness of the vaccine against hospitalization is 90% in those under 80 years of age, and drops to 87% in those of older age, according to the latest report on the subject from the Ministry of Health, dated October 3. The study also highlights that although there is a slight loss of effectiveness of the vaccine against infection after five or more months, for the group aged 80 and over, a “considerable” protection against infection and hospitalization is maintained.

Will it take a third dose for everyone?

For now there are no data to support a third dose for healthy people under 80 years of age, explains Marcos López-Hoyos, president of the Spanish Society of Immunology. This doctor indicates that severe cases among those vaccinated occur only in patients with previous illnesses and in those over 80 years of age. It is not clear why, but part of the explanation is due to the aging of the immune system and because this population group is also the one with the most additional diseases. “This is the group that should receive the third dose. For now, there is no reliable data that is needed for anyone else ”, highlights López-Hoyos.

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Can the transmission of the virus be prevented with vaccines?

Only with the vaccines available, no. But if basic prevention measures such as hygiene, a mask and distancing if necessary are added to them, transmission drops considerably. The simple use of the mandatory mask reduces the incidence of covid by more than 50%, according to a study with data from 200 countries published in the medical journal BMJ. For López-Hoyos, this is clearly the explanation for why countries like Austria or Germany are seeing such a steep increase in cases. “In these countries there are fewer people vaccinated and despite this they relaxed before the basic protection measures. This should make us think that we must maintain the use of a mask and the rest of basic hygiene measures, because today it is the only way we have to stop the transmission of the virus ”, he points out.

What will happen to the coronavirus?

In January of this year, a group of experts in viral evolution predicted that in between 1 and 10 years the covid would have transformed into an asymptomatic infection or, at most, into a mild cold. Of course, the SARS-CoV-2 virus will never disappear. For now, this is the most plausible scenario for countries with high vaccination rates such as Spain, López-Hoyos acknowledges. Like many other infections, including influenza, there will be occasional cases of severe infection in vulnerable people and some deaths will be inevitable, but in general, the population will be protected by vaccines and hygiene measures.

Can a new, more lethal variant emerge?

It is possible, but unlikely. Until now, all the versions of the virus that have become dominant have been the most transmissible – the British or the delta – and not the ones that best escaped the immune system and, therefore, could aggravate the disease – the Brazilian or the South African -.

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George Holan

George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.

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