I took the 1st dose of AstraZeneca vaccine. Will I be immunized if I get Pfizer now? | Brazil

The shortage of AstraZeneca vaccine against covid-19, which affects cities in at least five states in the country, led some places to use the immunizing agent from to do for the second dose of those who had taken AstraZeneca.

THE vaccine interchangeability it has already been studied and used in several countries around the world. In Brazil, it is recommended by the Ministry of Health for pregnant women who have taken the first dose of AstraZeneca.

See below for the main answers to the following questions about the strategy:

  1. I received the first dose of vaccine from AstraZeneca. Will I be immunized if the second is from Pfizer?
  2. So why do we keep the schedule with two vaccines from the same manufacturer?
  3. Is there any risk in mixing the two vaccines?
  4. Can we mix all the vaccines?
  5. Will this change the vaccine passport?

1. I received the first dose of vaccine from AstraZeneca. Will I be immunized if the second is from Pfizer?

Yes. In Europe, several countries used Pfizer to complete the regimen of those who had received AstraZeneca when this vaccine was discontinued due to very rare adverse effects. Furthermore, studies have proven its effectiveness.

“With thousands of people in Europe vaccinated with this scheme, it was found that the levels of neutralizing antibodies were even higher than among those who had taken the two doses of the same vaccine, AstraZeneca or Pfizer”, says infectologist Alexandre Naime, member of the Committee of Extraordinary Monitoring of Covid-19 of the Brazilian Medical Association (AMB).

2. So why do we keep the schedule with two vaccines from the same manufacturer?

According to Isabella Ballalai, vice president of the Brazilian Society of Immunizations (Sbim), the difference is small and does not justify changing the entire vaccine strategy in progress. “It’s a fact that we use more to think about the reinforcements. We know that, for the third dose, the ideal is the heterological scheme. The biggest challenge in Brazil since the beginning has been stock management for first and second doses, which is why the ideal is to stock up with the same vaccine. Studies published several months ago have already shown that this strategy is quite safe.”

3. Is there any risk in mixing the two vaccines?

According to Naime Barbosa, there is even less adverse effect for those who had mild reactions to the first dose of AstraZeneca. “We’re talking about the second dose in the context of circulating the delta variant, which requires two doses. You have no protection against severe forms of the disease caused by Delta if you haven’t received the second dose. That’s why these Pfizer stocks that arrived in Brazil should be prioritized to complete the schedule of those who took only one dose. This is the priority indicated by the Brazilian Medical Association (AMB). Then, we should give the booster dose to the elderly, vaccinate adolescents with comorbidities and, only then, vaccinate adolescents without comorbidities”

4. Can we mix all vaccines?

There are no studies on a heterologous regimen with CoronaVac, which has a shorter interval between doses. And Janssen’s vaccine is a single dose. So the possible scheme, so far, involves AstraZeneca and Pfizer.

5. Will this change the vaccine passport?

There is no consensus among experts on this issue. Entry into other countries will depend on the rules of each one. For Naime Barbosa, the strategy should not bring any problems because the vaccination schedule will be complete with two doses with vaccines recognized here and abroad. Thousands more people were vaccinated this way. Ballalai says that as this heterologous scheme is not yet routine abroad, having been used by countries where there was a shortage, as in Brazil, it may be that some of them will not accept it. When in doubt, it is important to confirm the rules of each destination before making a trip.