Third dose of the vaccine: why, when and how it would be given
The reasons why a booster dose is needed for those vaccinated against covid and what the mechanism is is part of what the Contestadog responds.
In recent weeks, the question of whether we will need a third dose of the covid vaccine has become a topic of scientific discussion and Sunday lunches. If you discussed it with your friends, family or office colleagues, the Contestadog, from WatchDog PAUTA, got the following question: am I going to need a third dose?
Vaccinated and with our mobility pass we went to find the answer. In Chile, as of Tuesday, July 20, 11,843,564 people had completed the vaccination process (either the two-dose or a single-dose schedule), that is, on the order of 78% of the target population.
Despite the high rate of inoculation, the Ministry of Health has already begun to prepare for the third dose, which could provide greater protection to people against the delta variant and those that occur in the future.
Countries like Israel have already started this process, while others like the United States, Germany and France are waiting for results that will ensure its implementation in the entire general population and not just groups or special cases. In Chile, studies are also being carried out before giving the yes.
The Undersecretary of Health, Paula Daza, assured that the current scenario suggests that a third dose will be needed. When? The date has not been confirmed, but it is said that it should be six months after completing the scheme to boost the level of antibodies.
Health experts say that the question of whether a third dose will be needed is not the only one, but also when and how to administer it.
By the way, there is talk of "third dose" because 96% of those who have the complete scheme have received the inoculations consisting of two injections (such as those of the Sinovac laboratories and Pfizer-BioNTech).
Why is it needed?
Sergio Lavandero, director of the Advanced Center in Chronic Diseases of the University of Chile, explains that "vaccines protect us from the coronavirus by generating levels of defense in our body against antibodies and protective cytotoxic T lymphocytes." When these defense levels drop after a few months, a third dose may be needed to raise them again.
Mario Rosemblatt, immunologist and executive director of Science & Life Foundation, shares that “it is normal that once the antigen has disappeared -either from the vaccine or from a natural infection with the virus-, the antibodies go down or disappear. The important thing is that the immunological memory, both cellular and of antibodies, remains ”. At that time a third dose would be necessary, since the permanence of the "immunological memory" is not entirely clear in the case of those vaccinated with Sinovac.
According to figures from the Ministry of Health, 75% of the immunized Chilean population was vaccinated with Sinovac. This is an inactivated virus vaccineTherefore, it has a lower immunogenic capacity than messenger RNA vaccines, and a greater possibility that the duration of immunity of the vaccinated person is shortened. The World Health Organization (WHO) recommended that those vaccinated with Pfizer-BioNTech and AstraZeneca-Oxford should also consider a third dose, and not just those vaccinated with Sinovac.
Is it possible to mix vaccines from different laboratories?
One of the biggest unknowns is whether people will be able to receive different vaccines than the ones they had in their first and second doses. According to Lavandero, “we must wait for the results to determine if we are revaccinated with the same previous vaccine or if there is addition of a different one. The latter also requires prior safety studies ”.
The question should be resolved with the clinical study that the Ministry of Health began on July 9, in which 560 volunteers participate and that will allow the conclusion of the best design to combat covid-19 and its variants.
The technique of mixing vaccines is already being used in Chile with those who received the first dose of AstraZeneca and completed their schedule with Pfizer. The question is what is the best mechanism: combine vaccines or keep the same for the third.
Something that Rosemblatt and Lavandero agree on is that the application of the third dose should be done in the same order that was applied this year, that is, giving priority to the elderly, health personnel, risk groups and then in order from oldest to youngest.
How often will we have to get vaccinated?
Both in Chile and in other countries there is still no consensus on how often the population should be vaccinated to protect it from covid-19. However, Mario Rosemblatt adds that "we do not have much evidence in this regard, but the few known cases indicate that after six months there are no problems and with a good response."
WatchDog PAUTA is a joint fact-checking project between the Faculty of Communication of the Universidad de los Andes and GUIDELINE. It seeks to take items on the agenda and track their veracity from a positive, not an inquisitive perspective.
The Contestadog section answers questions that come from the audience through social networks.