In places with a high percentage of vaccinated adults, infections seem to decrease at the same rate even among children not yet immunized.
Children not yet vaccinated against covid seem to enjoy the indirect protection of vaccinated adults: the first data coming from some realities that have completed or almost completed mass vaccination campaigns remove the initial fears that younger people, not yet vaccinated , can become “viral reserves”, and form pockets of the population in which the coronavirus continues to circulate freely. This does not seem to happen: indeed, in places where most adults are vaccinated, infections among children seem to drop at the same rate, due to herd immunity .
AN IMPRESSIVE REDUCTION IN CASES. An article published in Nature cites some examples of the indirect positive effects of anti-covid vaccines in children. The clearest evidence comes from the Brazilian town of Serrana, in the state of Sao Paulo, where 98% of adults have been vaccinated as part of a project to measure the real-world effectiveness of the CoronaVac vaccine, developed by the Chinese company Sinovac . Although the vaccine did not give exciting results in clinical trials (where it reached 50% efficacy), in Serrana it reduced symptomatic cases by 80% and deaths by 95%.
In the town, only 62% of the 45,000 inhabitants are adults: yet, a similar reduction in symptomatic infections has also been observed in children not yet vaccinated. Fortunately, concerns about the possible circulation of the virus between children and teenagers did not materialize.
MORE DIFFICULT TARGETS. In the US, where just over half of the population (mostly adults) received at least one dose, cases in under 18s dropped by 84% between January and May. The vaccinated population indirectly protects those not yet eligible for the vaccine, a concrete example of the concept of herd immunity. Viruses need hosts to stay in, and the fact that unvaccinated children do not appear to constitute reserves of viral circulation is probably due to the lesser ease of viral transmission in this population group. In the airways of children, cell receptors that allow SARS-CoV-2 to enter are less abundant.
WHO INFECTS WHOM? A valid indicator of the circulation of the virus among children is represented by infections in the school environment. In Israel, where the vaccination campaign has brought infections from 559 to 1.5 cases per 100,000 from mid-January to today, schools reopened in March. The children had not been vaccinated, yet infections in the under 11s fell the same way, from 546 to 1.5 cases per 100,000 people. According to Eric Haas, an epidemiologist at the Israeli Ministry of Health, this suggests that adults infect children and not vice versa , as was assumed in the early stages of the pandemic. Otherwise, when schools reopened, the children would be reinfected en masse.
ScienceThe covid inflammatory syndrome in children
HOW DO WE DEAL WITH THE VARIATIONS? However, there are two factors to consider in order to have a more objective picture of the situation. In Israel, the speed with which the vaccination campaign was completed may have crippled all the chains of viral transmission simultaneously, but not everywhere has it been possible to immunize so quickly, and with such a wide availability of doses.
The second factor to consider is the contribution of the variants . In the United Kingdom, where the vaccination campaign has continued apace, but the vaccination rate is around 60%, and where schools have reopened while the Indian or Delta variant was spreading (B.1.617.2), infections among children and young people have dropped, but not so strikingly. In secondary schools, cases went from 600 out of 100,000 in January to less than 100 out of 100,000 at the end of May. Outbreaks of two or more cases have occurred in about a hundred English schools – out of 25,000 institutions.
VACCINATE IMMEDIATELY, OR WAIT? This indirect protective effect, coupled with the fact that – according to estimates – only 0.14% of children with covid develop severe inflammatory forms, leads some epidemiologists to believe that before vaccinating children, vaccines must be shipped to countries that have not yet began to protect the elderly and health workers. It is also true, however, that no one knows the long-term effects of the virus, that even the very young can carry forms of long covid for months, and that the vaccination of school-age children and adolescents is considered essential to achieve herd immunity and protect adults who cannot be vaccinated for health reasons.
