The vaccine does not prevent transmission.
www.aamc.org/news-insights/6-myths-about-covid-19-vaccines-debunked
Myth #2: The vaccines don’t really work that well — they don’t reduce virus transmission.
Most experts have been urging people to continue following public health guidelines, including masking and social distancing, even after they’ve been fully vaccinated with two doses of the Pfizer or Moderna vaccine or one dose of the Johnson & Johnson vaccine — and after enough time has passed for those vaccinations to have taken effect (generally two weeks).
The reason for this recommendation is because while the Pfizer and Moderna vaccines have been shown to have 95% efficacy against illness (and the Johnson & Johnson vaccine is 85% protective against severe disease), the clinical trials were not designed to test whether any of the trial participants contracted COVID-19 but showed no symptoms.
“The experts are saying that the vaccines do not reduce transmission, but that is an inaccurate statement,” Gandhi says. “Vaccines have always decreased transmission. What they should be saying is that the clinical trials were not designed to test for asymptomatic infection, but there is every biological reason in the world to believe that they will reduce asymptomatic transmission.”
There is already evidence to support this, she says. First, when the vaccines were studied in macaque monkeys (during preclinical testing), they did eliminate asymptomatic infection — researchers swabbed the vaccinated macaques’ noses and found little or no virus. Second, the types of antibodies that are stimulated by most systemic vaccines (IgG and IgA) do tend to block viral infection in the nose (and no viral load in the nose most likely translates to no transmission). Finally, when monoclonal antibodies are given to COVID-19 patients, those antibodies reduce the viral load throughout the respiratory tract, including the nose.
The most convincing evidence, though, is just starting to emerge among real-world data. In Israel, where more than 90% of those age 60 and over have been vaccinated, “cases have plummeted in this population,” Gandhi notes. “Not just hospitalizations, which we expected, but cases [asymptomatic infection] as well.” Moreover, data from vaccinated health care workers recently published in the Lancet and preprint servers show reduced rates of asymptomatic infection and low viral loads in the nose when swabbing after vaccination.
“I think that in a few months, we are going to be able to say with certainty that these vaccines not only protect you, they also protect those around you,” Ranney says.