Can vaccines against covid-19 transmit the virus?

Now that vaccines against covid-19 arrive at health clinics, researchers turn to other questions that arise along with variants of the SARS-CoV-19 virus: will those who are immunized be protected from all strains that are emerging? Will vaccinees be able to develop or even transmit the disease? The answer is: we still don’t know.

Scientists from dozens of institutions and laboratories, such as those from Pfizer, maker of the BNT162b2 gene vaccine, and the University of California, which maintains the program Long-term Impact of Infection with Novel Coronavirus (LIINC), are now studying the role of the vaccine in stopping the so-called progressive transmission of the disease.

LIINC researcher Leo Torres examines the blood sample of a volunteer infected with covid-19.Source: LIINC / Disclosure

“There are three things that a vaccine can do: prevent you from getting the disease completely, stop progressive transmission and stop symptoms,” he told MIT Technology Review biologist and public health and infectious disease researcher Jeffrey Shaman of Columbia University.

Roughly speaking, there are two types of vaccines: the perfect type (gold standard) causes what is called “sterilizing immunity”, that is, the virus cannot infect the body. An example of this type is the smallpox vaccine, eradicated from the planet (on October 26, 1977, the last case of naturally transmitted disease was recorded in Somalia).

The virus that causes smallpox, a disease eradicated from the planet.The virus that causes smallpox, a disease eradicated from the planet.Source: Callista Images / Reproduction

“Sterilizing immunity means that you don’t carry any viruses. The antibodies and the immune response you generate eliminate it completely from your system, ”says pathologist Dawn Bowdish, of McMaster University.

Low viral load

The consequence of taking a vaccine that causes sterilizing immunity is that the individual who receives it will not transmit the disease to those who did not get it – unlike those who receive the second type of immunizer, which allows infections to develop in the body, but in a light or even imperceptible way (that is, without symptoms).

The antibodies produced fight infection, but the individual still carries a certain amount of the virus in the body, and can transmit them to those who have not yet been vaccinated.

Members of the Mukuru indigenous village in Amapá are vaccinated against covid-19.Members of the Mukuru indigenous village in Amapá are vaccinated against covid-19.Source: Ministry of Defense / Disclosure

That is why, even with the distribution and application of different immunizers progressively increasing worldwide, researchers now need to know whether whoever receives them will be, even vaccinated, a vector of the disease.

This will determine the course of the fight against the pandemic: if masks are still needed and for how long; how the populations of the most affected countries will behave; and the degree of confidence about the benefits that vaccines can bring.

Modeling effectiveness

As soon as Pfizer started distributing its vaccine, it began to accompany volunteers in the US and Argentina to try to find out how often those who were immunized can develop asymptomatic coronavirus infections – it is already known that someone who is vaccinated does not develop the severe form of disease (one that needs a respirator in an ICU), but covid-19 is not yet transmitted.

While data is being collected, some universities, like Emory, have tested computer models to measure the effect of vaccines in blocking virus transmission: the conclusion is that a good vaccine can stop the spread, but not the disease – even so , fewer people would die, because the outbreak would be delayed long enough to prevent more individuals from becoming infected.

Masks and social distance will probably still be needed, even with vaccination.Masks and social distance will probably still be needed, even with vaccination.Source: Getty Images / David Ramos / Reproduction

Since last year, physician and computer modeling specialist applied to Public Health and Health Policy Bruce Y. Lee has studied the effectiveness of covid-19 vaccines. In an article published in American Journal of Preventive Medicine, Lee and other researchers modeled the impacts of the various levels of protection against the disease via collective immunization.

The results indicated that if a vaccine has a protection rate of 80% and if 75% of the population is immunized, the covid-19 pandemic can be stopped without other measures such as social distance. “Otherwise, you will not be able to rely on the vaccine alone to return to ‘normal’,” he says, reinforcing a general mistrust that has not yet been proven: the evidence so far suggests that vaccines should reduce the chance of transmission, but they cannot eliminate -there.

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