This is what you need to know about the additional doses proposed to some groups of people, especially because of the arrival of the Delta variant
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Q. Why is the third dose of the Covid-19 vaccine necessary?
R. Because it has been seen that, despite the vaccine efficacy in severe cases of Covid-19, its efficiency in fighting the virus decreases over time. What is known so far is that the antibodies decrease little by little and during the winter the possibility of contagion increases. That is why it has been decided to be prudent in scheduling a third booster dose. It is not known what will happen during the next six months and, at this dose, those most at risk will be safer.
Q. What is the difference between the “third dose” and the “booster dose”?
R. The third dose can be put at 28 days of the second and is intended to complete the vaccination cycle in immunosuppressed people, that is, in those people whose body has not responded effectively to the first two doses. Rather, the booster dose should be inoculated at least six months later of the second dose. In fact, it is considered a second round of vaccination and it takes longer to reactivate the production of antibodies.
Q. From what moment has there been a decrease in the efficacy of the vaccine?
R. On average, between six and nine months after being vaccinated. As has been observed, there is a modest decrease in protection against infection. This decrease varies in percentage depending on the vaccine we are talking about.
Q. Is protection against the virus low in all people? What does it depend on?
R. The older the person, the worse their immune system responds. The first variable that affects the decrease in the effectiveness of vaccination is the age, although there are also other individual factors that are still being investigated.
Q. Does the loss of efficacy affect all vaccines?
R. Yes though Modern it appears to be a somewhat more stable vaccine. According to the studies carried out, it has a higher messenger RNA concentration than that inoculated by Pfizer and, for the moment, it seems to be the vaccine that is least weakened.
P. Does the time that passes between the inoculation of the first and the second dose also influence?
R. Not seem.
Q. What are the indications for Johnson’s vaccine, which is a single dose?
R. Who has received this vaccine is as if they had only received one dose of AstraZeneca (since the two vaccines are very similar). Therefore, they should be the first to get an additional booster dose, without waiting the statutory six months and regardless of their age. This is because a single dose of the vaccine tends to have a more difficult time inducing an immune memory response. In fact, already in phase III studies, Johnson’s vaccine demonstrated less efficacy.
Q. What criteria should the third dose and booster dose schedule follow?
R. Age and risk of serious illness in case of catching Covid-19. People over 60 years they are more prone to hospitalizations because their immune systems are weaker and therefore should be a priority in booster doses. In the case of the third dose, on the other hand, the EMA (European Medicines Agency) establishes another order: immunosuppressed, over 80 years old, health personnel and over 60 with previous pathologies.
Q. Does getting vaccinated again enhance the effect of the first vaccination cycle?
R. It is precisely a way of enhancing the response of the immune system that can even exceed the level of defense achieved with the two initial doses.
Q. How long will the effect of the vaccines last?
R. It is not yet known. There are currently two unknowns: it is not known how long immunity lasts and it is not known either how the virus will vary in the future. If it changes little, the improved vaccines will likely last several years. However, if the virus continues to mutate, a new vaccine may have to be made in about a year.
Q. Is the third dose necessary because of the arrival of the Delta variant or because of the loss of efficacy of the vaccination?
R. It was anticipated by the appearance of the Delta variant because, being much more transmissible, it can also infect the vaccinated (with very low percentages compared to the unvaccinated). This changed the existing scenario. In any case, at some point it would have been equally necessary to reinforce the effect of the vaccines with additional doses, although perhaps later.
Q. How safe is it to take a booster dose?
R. It is not yet known for sure. The EMA approved it for everyone, while the US regulatory agency has only approved it for the weakest people.
** Answer the questions Antonella Viola, immunologist at the University of Padua.
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