WILL THE VACCINES STOP THE CORONAVIRUS?

 

Controlling the pandemic will need vaccines that stop the spread of the virus, a property that is difficult to measure and difficult to achieve.

As countries deploy vaccinations to protect themselves from COVID-19, it is being studied whether the injections also stop those vaccinated from being infected and from spreading SARS-CoV-2. Vaccines that prevent transmission will help keep the pandemic under control, if given to enough people, making it increasingly difficult for the virus to find people it can attack.

Preliminary analyzes suggest that some vaccines are likely to be able to stop the transmission of the virus. But it is not easy to confirm this effect or its forcefulness, because a fall in infections in a given region could be explained by other factors, such as confinements and changes in customs. Furthermore, since asymptomatic carriers also spread the virus, detection of such infections is very difficult.

Will they stop the infections?

Although most clinical trials of COVID-19 vaccines were shown to protect against the disease, there was also evidence that they might prevent infections. A vaccine that is very effective in preventing those vaccinated from becoming infected would help reduce transmission from the outset.

During the trial of Moderna's vaccine, made in Boston, all participants were swabbed for traces of viral RNA. Compared with those who received a placebo, a two-thirds decrease in asymptomatic infections was seen among those who injected the first of the two doses of the vaccine. But since it was only checked twice in each person a month apart, some infections could have been missed.

In the British trial of the vaccine produced by the University of Oxford and AstraZeneca, participants underwent nasopharyngeal swabs every week and asymptomatic infections were estimated to decrease by 49.3 percent in a subgroup of vaccinated compared to the group without. vaccinate.

New York-based Pfizer, the maker of another leading-edge vaccine, has said that to see if its injections can block the infection, it will begin swabbing participants every two weeks in ongoing vaccine trials. carried out in the United States and Argentina.

Will the contagions decrease?

Vaccines may not prevent infections or reduce them significantly. But if once administered they make those infected less infectious, they would help reduce transmission.

Several research groups in Israel are measuring the "viral load" (the concentration of virus particles) of vaccinates who have later tested positive for SARS-CoV-2. Viral load has been found to be a good indication of contagion.

In preliminary work with people who had received the first dose of the Pfizer vaccine, a significant drop in viral load was observed in a small group of those infected with SARS-CoV-2 after 2 to 4 weeks, compared to with whom they were infected in the first 2 weeks. The data is certainly interesting and suggests that vaccination would reduce the contagiousness of COVID-19 cases, even if the infection is not completely prevented. The Oxford-AstraZeneca trial also found that a small group of vaccinated decreased viral load more than in the unvaccinated group.

But for other researchers it is not yet clear if this drop in viral load will be enough to make us less infectious in real life.

Benchmark

To determine whether vaccines stop transmission, close contacts of those vaccinated are being traced to see if they have indirect protection against infection.

As part of the PANTHER study carried out in England with hundreds of health workers, researchers at the University of Nottingham analyzed whether health workers and the people who lived with them had viral RNA and antibodies against SARS-CoV-2 between April and April. August 2020 (around the first wave of the pandemic). According to Ana Valdes, a genetic epidemiologist at the University of Nottingham, after receiving the Pfizer vaccine, some of the health workers and their close contacts who have not been vaccinated will be re-analyzed to see if the risk of infection has decreased in these last. If it decreases, the vaccines are probably blocking transmission.

In Israel, it is also planned to study the households in which a member has been vaccinated. If the vaccinated are infected, it will be possible to see if they spread the virus to another partner.

In a trial in the Brazilian city of Serrana and over several months, the doses of the COVID vaccine will be distributed in stages and at random