One of the doubts that arises from the beginning of the vaccination program against covid-19 is whether the vaccines also prevent infection (asymptomatic forms) in addition to preventing the disease and its complications (hospitalizations and deaths). The clinical trials did not allow an answer to this question, since naive people were included, that is, people who had not suffered from covid-19 previously, and possible cases were not followed up in the absence of symptoms.
Resolving this question is very important because it allows the desired group immunity to be achieved more effectively.
Resolving this doubt is of great importance, since if the vaccines also protect against infection, they will allow to control the transmission of the virus and achieve much more effectively the much desired group immunity.
The first data and studies on this topic are beginning to be published. A study carried out by the Public Health Agency of England indicates that the risk of vaccinated adults transmitting the virus to people with whom they live is much lower than in those who are not vaccinated. The study has included 552,984 people who lived at home with someone with Covid-19, and who therefore could be considered close contacts. When the covid-19 case was an unvaccinated person, 10% of the contacts were infected, while if the case had received a dose of AstraZeneca or Pfizer vaccine at least 21 days ago, the percentage of infection in the contacts was reduced to 5.7% and 6.2%, respectively, for each type of vaccine. The authors conclude that for adults who became infected with coronavirus three weeks after receiving vaccines from Pfizer or AstraZeneca, the risk of intrafamily transmission was 40-50% lower than for adults infected but not vaccinated.
The reduction in the risk of contagion is observed already from day 14 after vaccination, which corresponds to the time it takes for our body to generate protective antibodies. And, also very relevant, this risk reduction does not depend on age, gender or the intensity of contact. Anyone who lives with a vaccinated person benefits from this lower risk of becoming infected. This effect could be even greater in contacts of people vaccinated with two doses.
These results are comparable to those of another study conducted in Scotland that also showed a lower risk of infection in household contacts of vaccinated healthcare professionals.
We are leaving the toughest times of the covid pandemic behind us, but we cannot relax
Why do vaccinated people transmit the virus less? The viral load in vaccinated people who become infected is lower than in those not vaccinated, which would explain this lower transmissibility.
The fact that vaccination reduces not only the risk of developing a serious disease, but also the risk of infecting it, is another great news in the fight against the pandemic. Although these results only refer to the home environment, this is the one with the highest risk, since the degree of contact between cohabitants is higher than in other environments, with secondary transmission rates of up to 37%, according to some studies. We are leaving the toughest times of the pandemic behind us, but we cannot relax. A vaccinated person can also become infected, and a vaccinated person can also infect. It is less likely, but it is possible.
Magda Campins She is head of the Preventive Medicine and Epidemiology Service at the Vall d’Hebron Hospital in Barcelona.
Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.