how long immunity lasts with a single dose

Although its administration is not yet planned in Argentina, the “light” version of the vaccine Sputnik V, authorized by Russia, was received as positive news by a large part of the scientific community; given the context of the epidemiological emergency, plunged into a scenario of global vaccine shortage.

However, they persist doubts and questions in the absence of publications and scientific studies referring to the duration of the immune response over months and during how long are the neutralizing antibodies kept. Is it necessary to apply reinforcement? In research, the data is unknown.

The new strategy developed by the Gamaleya Institute of a single component (Adenovirus 26, the same non-replicative human adenovirus that contains the first application of Sputnik V) and a single dose, is identical to the first half of the “traditional” vaccine whose effectiveness against COVID-19 is 91.6% (every 100 people vaccinated only between 9 and 3 can be infected). In addition, it is effective against all new strains of coronavirus, according to the results of laboratory studies at the NITsEM NF Gamaleya Center ”.

In phases 1 and 2, the vaccine was shown to be immunogenic and safe. Currently, he is going through phase 3 of the research. The Russian Direct Investment Fund (RDIF) determines that the light version protects by 79.4% (20 out of 100 may be infected), after 28 days from administration. How did you calculate this level of efficiency? They applied the following formula: the incidence of Covid among the unvaccinated population (1.349%) minus the incidence among the population vaccinated with one dose (0.277%), then divided by the incidence among the population. unvaccinated (again, 1.349%). ).

“The vaccine is tested in two doses of different components 21 days apart. It is known that on day 21, the protection provided by the first component against clinical disease was 72%. The effect of vaccination in this group of people who have received a single dose should be explored, beyond the 21st day after vaccination.

“Outside of this period, the Gamaleya Institute only reported that the efficiency was around 80%, but there are still scientific publications that support it. Patients who have had COVID and who are subsequently vaccinated with a dose of Sputnik develop a high antibody response. Maybe, in this group, the light program has more bases until more information is available ”, analyzes Martín Stryjewski, head of hospitalization at CEMIC and Master in health sciences of the Duke University (NC, USA).

In principle, the efficacy data is superior to that of many other vaccines which require two doses. But it will be necessary investigate whether or not it loses its effectiveness over time. For a large sector of the library, this could be an excellent alternative to reach a larger number of the population in a short time.

“It is true that the efficiency is slightly lower, also much higher than the 50% required by the WHO. There are experiences around the world, mainly in the UK, of how the incidence of covid cases, hospitalizations and deaths has been dramatically reduced with the mass vaccination of people with a single dose. I believe that the number of people who can be vaccinated in less time is more important than the percentage of clinical effectiveness, ”says Leda Guzzi, infectious disease specialist and member of SADI.

Doubts about immunity

According to the Gamaleya Institute, immunization with the light version allows the development of antigen-specific IgG antibodies in 96.9% of vaccinated people, 28 days after application. They also ensured that from this moment there is neutralizing antibodies in 91.67% of people who received this unit dose.

“The duration of the immunity will be known over time. This will likely require boosters or reinforcements, but the most important thing now is to quickly control the viral spread “Underlines Guzzi. This is because, a priori, the single-dose regimen proposed by the light version does not require a second application to complete the immunity. But, if over time it is observed that the neutralizing antibodies start to fall, reinforcement could be put in place.

Guillermo Docena, biochemist, immunologist and principal investigator at Conicet, points out the likelihood that the antibodies will last for a short time. “In general, after two months the levels drop. What remains and gives you long-lasting immunity are the cells that generate them (memory B cells). The ability to produce neutralizing antibodies is long lasting and this is what gives you a memory over time so that in case of reinfection antibodies are produced again “, Explain.

Another information about which there is no certainty is whether the immunity conferred by the vaccine lasts less in the absence of the second component which strengthens the immune response evoked by the first. “For example, almost a third of patients who have anti-COVID antibodies after a natural infection, they lose them within 6 months. Whether the same would happen with people inoculated with Sputnik, and / or whether the possible loss of antibodies would be associated with a loss of immunity, has not yet been resolved, ”says Stryjewski.

“Probably, with the strategy of converting the vaccine into a single dose, the duration of the antibodies is shorter because, in general, all vaccines are scheduled with first doses and boosters. In a context of scarcity and inequality of vaccines, it can be considered as an alternative, but we cannot assume that the protection will be the same than with a complete vaccination ”, summarizes Waldo Belloso, a doctor specializing in infectious diseases.

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