The Journal of American Medical Association (JAMA) has published an Editorial commenting the data obtained by different studies that try to clarify the reasons for coronavirus infection in already vaccinated people, as well as the need for vaccine reinforcement against the Covid-19.
It is known that after complete vaccination (administration of the two doses of vaccine), the risk of infection by the coronavirus persists, although this risk decreases significantly. For example, in a study carried out in England during the peak of transmission of the Delta variant, it was found that among vaccinated people (n=55,962) the possibility of having the coronavirus was two-thirds lower than among unvaccinated (n=15,135).
It has also been shown that in vaccinated people who become infected, the amount of coronavirus that is detected decreases earlier and faster than in unvaccinated people, so they have less capacity to infect other people and the disease they develop is less severe.
Incidence in cases of hospitalization
Thus, among all the cases hospitalized for COVID-19 between March and August 2021 in the United States, only 15.8% of these admissions corresponded to vaccinated people. The protection of the vaccinated is also similar against the Alpha and Delta variants of the coronavirus. However, it has been found that 6 months after receiving the second dose of Pfizer’s RNA vaccine, its effectiveness may decrease by 50% or more.
This suggests that another booster dose of the vaccine should be given. In this sense, the data obtained in Israel show that protection against the coronavirus is restored after the administration of a booster dose.
Efficiency over time
In summary, vaccines are highly effective in preventing coronavirus infection and in case of infection, the disease is less severe. However, many aspects remain to be clarified, such as the duration of protection after the administration of the booster dose of the vaccine or whether it will be necessary to re-vaccinate from time to time.
On the other hand, the required amount of antibodies that confers protection against virus infection is unknown. Furthermore, when the antibodies decay or disappear, memory B lymphocytes could theoretically protect against the virus. If this hypothesis is confirmed, it would not be necessary to administer booster doses of the vaccine.