The more data we get, the more it seems that people who are vaccinated do not spread the coronavirus

Now that effective coronavirus vaccines are licensed and distributed, the crucial question is: Does it stop transmission?

In clinical trials, Pfizer and Moderna have shown their injections to prevent severe COVID-19, but they have not tested whether their vaccines prevent asymptomatic cases. Without reducing these symptomless infections, it is difficult to stop the transmission of the coronavirus from person to person. But the evidence is gathering around the idea that people who receive these vaccines are not spreading the virus after all.

“There have been studies that point in a very favorable direction,” Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a briefing last week.

A preliminary study from Israel, for example, found that as of 12 days after vaccination, people who contracted COVID-19 despite Pfizer’s vaccines had four times less virus in their bodies. Reduced viral loads are linked to lower transmission rates.

“We are convinced that vaccination against COVID-19 reduces the chances of transmission of the virus,” Mr. Kate Grabowski and Justin Lessler, two Johns Hopkins epidemiologists, wrote in the Daily Beast last week, adding: “It is may be that protection against transmission. is significantly less than protection against serious disease, but at this point it would be more than shocking if there was no impact. “

Johnson & Johnson’s single-dose COVID-19 vaccine, although not yet licensed in the United States, also appears to be effective in preventing asymptomatic infections, according to data released by the Food and Drug Administration on Wednesday.

The story continues

Vaccinated people may be less contagious if they are infected

Research shows that the more viral particles a person has in their mouth and nose, the more likely they are to pass the coronavirus to others.

“In other words, a higher viral load, good transmissibility; a low viral load, very low transmissibility,” Fauci said.

So a vaccine should reduce transmission if it can ensure that even those who still contract the coronavirus after their injection – whether symptomatic or asymptomatic – have a lower viral load than they would have. other.

The recent Israeli study, which has not yet been peer reviewed, suggests that is the case with the Pfizer vaccine. Researchers examined more than 1,000 people who had tested positive for the virus after being fully vaccinated in Tel Aviv. The viral load of these people in the 12 to 28 day period after their second dose was four times lower than their viral load in the first 11 days after their vaccination.

“These reduced viral loads suggest a lower infectivity, further contributing to the impact of the vaccine on the spread of the virus,” wrote the study authors.

Another study from Israel, which has not yet been peer-reviewed, suggested that Pfizer’s vaccine lowered viral load by as much as 20 times.

Some research suggests that viral loads are related to the severity of the disease, so a patient with a lower viral load is also less likely to have severe COVID-19. This may in part explain why Pfizer’s vaccine drastically reduces the risk of symptomatic infection.

Vaccinated people are less likely to develop asymptomatic infections

To determine whether vaccines really reduce the spread, it is essential to determine whether vaccines prevent asymptomatic cases of COVID-19 in addition to symptomatic infections.

Pfizer and Moderna clinical trials only tested volunteers for COVID-19 if they felt sick. Otherwise, companies should have demanded regular COVID-19 testing for the tens of thousands of volunteers. So, at first, neither company could say whether their vaccines prevent asymptomatic cases.

But Moderna tested trial volunteers the day they received their second injection. And the results suggest that there were fewer asymptomatic infections among the participants who received the real vaccine than among those who received a placebo. Only 14 of the 14,000 and over vaccine group in the trial had asymptomatic cases that day, compared to 38 in the similarly sized placebo group.

That’s a drop of 61.5%, according to Marm Kilpatrick, a disease ecologist at the University of California, Santa Cruz. He written on twitter that data suggests Moderna’s vaccine blocks about 91% of transmission.

Animal studies offer similar results: An October article found that the Moderna vaccine prevented the coronavirus from replicating in the nose, throat and lungs of rhesus macaques four weeks after they were vaccinated. If the viral particles cannot copy each other, it is unlikely that an infected host will transmit the particles to others.

As for Pfizer’s vaccine, new research in Israel (although not peer reviewed) suggests that the vaccine reduces asymptomatic cases by 89%, Reuters reported. Likewise, a preliminary study published in The Lancet found that Pfizer’s vaccine was at least 85% effective in preventing any type of infection – symptomatic or asymptomatic. The study involved more than 23,000 healthcare workers in UK hospitals.

“We provide strong evidence that vaccination of working-age adults will significantly reduce asymptomatic and symptomatic SARS-CoV-2 infection and therefore reduce transmission of infection to the population,” wrote the authors of the study. (SARS-CoV-2 is the clinical name for the coronavirus.)

Data from Johnson & Johnson’s clinical trials on asymptomatic infections also appear promising. The company tested blood samples from nearly 3,000 participants for one type of antibody to the coronavirus 71 days after being vaccinated. (The presence of this antibody suggests that the participants had been infected even though they had no symptoms.) Only two vaccinated people tested positive, while 16 people who received a placebo did.

This suggests that J & J’s vaccine may be 74% effective against asymptomatic infections, although the FDA has noted that more data is needed to be sure.

“There is uncertainty over the interpretation of this data and definitive conclusions cannot be drawn at this time,” the agency said.

Even the Oxford-AstraZeneca vaccine, which is still in clinical trials in the United States, can reduce asymptomatic infections.

An Oxford study, which has not yet been peer reviewed, found that among people who received only one dose, the number of positive COVID-19 tests – among symptomatic and asymptomatic study participants – fell 67%.

Read the original article on Business Insider