Why is the AstraZeneca vaccine given as a booster dose in Ecuador?

Since last December 1, the Ministry of Health of Ecuador opened the booster vaccination to the population over 18 years of age due to the appearance of the omicron variant of SARS-CoV-2, which causes COVID-19.

Although there are still aspects of this variant that are being discovered, the World Health Organization has already classified it as a concern due to the mutations it registers.

One of the measures that are being applied is to speed up vaccination for those people who have not yet administered a dose or to reinforce those who have already completed six months of the second. Regarding the decision to place the AstraZeneca vaccine as a booster, several people have thought that it is due to a large stock of doses in the country. However, according to information posted in the Social Observatory of Ecuador, 4’429,210 doses of AstraZeneca have arrived in the country until last November 16 and according to the state vaccinometer they have already been placed 3’148.652 doses (between first, second and booster) until December 7, that is, there is still a stock of a little more than 1.2 million doses.

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The booster dose with AstraZeneca will be given to those who have already exceeded six months when receiving the second dose of Pfizer, Sinovac, Covishield, Moderna, Novavax, Sputnik V, Sinopharm, Covaxin, Anhuei Zhifei Longcom, as well as AstraZeneca itself; one dose of Sputnik Light and three doses of Abdala.

Those vaccinated with Janssen / Johnson will receive booster doses from Pfizer; instead with CanSino they will receive the same vaccine. “People over 12 years of age with immunosuppression will receive a booster dose according to the homologous scheme; that is, with the same vaccine that they received previously, ”the Ministry specified in a statement.

The doctor in Medicine and PhD in Pharmacology, Enrique Terán, clears several doubts that Ecuadorians have about the booster process and the AstraZeneca vaccine:

Why is the AstraZeneca vaccine being used as a booster dose in Ecuador?

There was a lot of controversy regarding the AstraZeneca vaccine, the country was involved in this controversy about the safety that the vaccine could have and at the time of greatest vaccination people did not even want to receive AstraZeneca … The explanation behind is that From the evidence we have, which always ends up being insufficient, when we want to boost the immune system “it is better” or it is more effective to exchange vaccines then those who received two doses of Pfizer can receive a third dose of Pfizer, but apparently if they get a third different dose which may be AstraZeneca, which may be Johnson & Johnson the immune memory response is greater than if you received the same vaccine. It is not something formal, that is, The exchange of vaccines does not have to be mandatory, but it seems that it may be a better strategy. So people can ask and what happened if I received two from AstraZeneca what are they going to put on me, the logic would indicate that they should receive Pfizer for precisely this phenomenon of greater empowerment to occur, but it is still hypothetical, it is not something established and therefore so much any booster dose that can be received will produce a positive response in memory.

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On this point, the Ministry of Health, in its guidelines indicates that clinical studies showed that those who received two doses of an inactivated vaccine (CoronaVac) and then the booster with AstraZeneca presented higher levels of IgG against RBD, in addition to greater activity neutralizing against original variant and emerging ones. He mentions that a study in Chile showed that reinforcing any of the three vaccines (Pfizer, AstraZeneca and Sinovac) was able to significantly increase the effectiveness against illness and hospitalization.

In contrast, a booster dose of AstraZeneca for those who received the previous two induced “antibodies at a level that correlates with high efficacy after the second dose and increases T-cell responses.”

What is the difference between a third dose and a booster dose?

The logic behind is that not all vaccines had a two-dose schedule originally, for example, the Johnson & Johnson vaccine in the United States was a single dose, we have the CanSino vaccine that was used here in the country of only one doses and there are some vaccines in development that are of three doses so To speak of a third dose would generate a certain confusion that only and exclusively those who have received a two-dose scheme should receive the same, so it was decided rather to be able to estimate that we have a booster dose… It is highly probable that this concept of booster doses has to be done periodically and therefore, for now, it would seem that we are going to have to receive a booster dose every six months, ideally if the vaccines are optimized it could be that we have to receive an annual booster as is happening with influenza.

Will I get adverse reactions like clots when I get the AstraZeneca vaccine?

There is of course a subjectivity in this type of process, there are people who say I when I started Pfizer absolutely nothing happened to me and now that I put on the AstraZeneca reinforcement it hit me a lot, I had impressive discomfort. There is no logical reason why taking the booster dose would produce a major adverse reaction. that the one that would have been had if it is that it was the first or the second dose that was received; So there we must make a call to the tranquility of the population that does not have to suggest that a booster dose of AstraZeneca is going to be bad for them.

The Ministry of Health specified that the booster doses of AstraZeneca for those who received the same vaccine before were less reactogenic than the first two. In addition, it was explained that the reporting rate of vaccine-induced thrombotic immune thrombocytopenia was 8.1 per million vaccinated in the first dose and 2.3 per million vaccinated after the second dose.

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Why is a heterologous vaccination schedule better?

From what we understand is that the immune system is unable to generate a sustained response to SARS-CoV-2, using different types of platforms, that is, vaccines of different manufacture, can generate a better response and perhaps a little more lasting. . That will only be seen over time, but the hypothesis is that by changing, for example, Pfizer which is nucleic acid but AstraZeneca is a vector, then by changing from that platform it may be that the immune system reacts better and may last longer. It will be necessary to see because it is not known exactly what happens if two nucleic acids are placed if they are put, for example, Pfizer and Moderna, a better response is also generated but there is not enough evidence yet; That will only be seen four or six months from now what has happened with these reinforcements.

Why are those of CanSino given the same vaccine?

Because as with the Johnson & Johnson vaccine, as it was a single dose, then the manufacturer says: ‘we have done the studies and if you applied only one when you got the second, it acts like the booster that he had the two-dose vaccines’; Then it will give better results to apply a second dose of the same with the only difference that there has been a greater separation between the first and second dose but it will give the equivalent result. There are some studies of the Cansino vaccine that when it is applied four or six months later it achieves a protection close to 90% while the single dose was with an efficacy around 68%.

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Is getting vaccinated going to protect us against the omicron variant or the new ones that arise?

Yes, we will undoubtedly protect what is not certain yet is how much protection decreases against omicron because against delta we saw a significant decrease. The vast majority of vaccines lowered the protection versus delta by almost 40%, that obviously makes the risk slightly higher, but with omicron we still don’t have a certainty. At first it was said that the reported cases had been in fully vaccinated people. Now that the number of cases has increased there is no longer so much certainty and it seems to be that of course it affects the unvaccinated more than the vaccinated, but there is still no concrete number of how much the protection of vaccines against omicron.

If I got COVID-19, am I not already supposed to be protected against the disease?

In the case of omicron, it seems that it is much more marked that the natural disease does not provide enough protection, so whoever had the disease cannot feel calm that they will be protected from this new variant and there that (it is necessary) to reinforce, which is It is preferable to get the vaccine to improve protection. Those who are vaccinated at the moment with two doses in theory are protected against the original variant against the native one, but as these new variants continue to appear, they put themselves at risk again; At the same time, as it seems that the immunological memory is falling, that person begins to lose that protection, so the recommendation for the country in general is to increase the number of global vaccinated. We must continue to insist that it is convenient for us that more people are vaccinated because the more people are fully vaccinated, with the two doses, the less possibility of virus circulation in the environment and therefore less dangerous. And for those who are already serving more than six months it is the call for this booster dose to keep their immune system fresh and not put themselves at risk of a new infection because we still do not have a good number of people vaccinated.

What lessons have these two years with COVID-19 left us?

There is no doubt that, thanks to vaccination, mortality has been largely controlled. The indicators that we have of deaths in excess of ICU beds, etc., show that the vaccine works. Undoubtedly the appearance of these, let us call these alerts, as omicron also make us understand that it is not a spontaneous phenomenon because someone could say: ah yes, but after two years the virus was already attenuated and it was not necessary so much trouble; the appearance of these new variants makes us see that the thing has not yet been spontaneously controlled. (I)