Current COVID-19 vaccines prevent the person receiving them from getting sick, especially very sick, and needing to enter an intensive care unit. However, it is still unknown whether or to what extent those approved so far also protect against transmission of the virus. That is, a vaccinated person could become infected without developing serious symptoms, but continue to infect.
EU governments now compete with each other for COVID-19 vaccines
Therefore, despite having received the vaccine, one must follow with all the protection measures to avoid contagion: use of face mask, washing hands, distance security and ventilation of closed spaces. “We do not get tired of repeating it,” he says. Sonia Zuniga, virologist at the National Center for Biotechnology of the Higher Council for Scientific Research (CNB-CSIC).
Vaccines approved in Europe are capable of inducing a good immune response and they generally have very high degrees of effectiveness. But in clinical trials to demonstrate its efficacy and safety, it has only been observed if the drug prevents COVID-19 and protects people who are at higher risk of complications, no data has been published on whether they also stop the transmission of the virus .
The evidence on immunity
The results of the trials published so far show that, on the one hand, vaccines contribute to the immune system making neutralizing antibodies, part of the IgG immunoglobulins detected by serological tests. And, on the other hand, they also activate specific cells of the immune system – the T lymphocytes-, training them to be able to attack SARS-CoV-2 in case of infection.
This immune deployment prevents the virus from attacking the lungs, where it takes up residence and causes severe acute respiratory syndrome pneumonia. But there is a lack of data to know if vaccines also induce a similar immunity in the mucous membranes, where the virus ‘sneaks’ into the body.
In the nose and throat live another type of antibodies, IgA immunoglobulins, which ‘sweep’ the entry of respiratory viruses, such as SARS-CoV-2. If the virus colonizes the upper respiratory system, the pathogen is able to survive, even though it does not cause severe forms of COVID-19. That is why it is so important to maintain the use of masks, hand washing, distances and ventilation, which minimize the risk that the nose continues to be a source of contagion for other people.
In the animal studies there is also no protection against virus infection in the nasal passages, suggesting that transmission may continue. The pathogen survived in the noses of vaccinated non-human primates and subsequently exposed to the virus, despite the fact that the viral load was lower than in non-vaccinated ones, according to preclinical studies by Moderna.
“We do not know how much virus is transmissible,” he warns Beatriz Mothe, a specialist from the infectious diseases service and one of the researchers conducting the clinical trial of Janssen’s vaccine at the Germans Trias i Pujol Hospital, in Badalona. “In addition, we do not have information on the immunity that vaccines produce against the new variants,” he adds.
For his part, Zúñiga points out that preliminary data of vaccination in Israel, the country with the most advanced immunization plan, suggest that the transmission of the virus is declining, although it is still unknown if the vaccines prevent infections. “One possible explanation is that the viral load is lower and you are less likely to infect, although it is not yet clear,” he explains cautiously.
Vaccination prioritizes the elderly and vulnerable
The vaccines approved for now in Europe – which as of March 17 are those of Pfizer-BioNTech, Oxford-AstraZeneca, Moderna and Janssen – are administered by means of two punctures in the arm, separated by less than a month apart. “Intramuscular vaccination is not the most appropriate to induce mucosal immunity and IgA production,” says Zúñiga. The expert adds that a vaccine for intranasal and oral administration takes much longer to develop than the current ones.
In Spain, as in many other countries, the vaccination strategy prioritizes vulnerable groups and the elderly, since age is the main risk factor for hospitalization and death. The reason for vaccinating priority groups, such as residents of non-institutionalized centers for the elderly and highly dependent, is to protect them from the most serious forms of COVID-19.
In conclusion, vaccines against COVID-19 prevent the most serious forms of the disease. Its objective is to reduce mortality from the virus and prevent the health system from collapsing. For this reason, even though a person has received the vaccine, they must continue to maintain all protective measures.