Applying 2nd dose of Pfizer to those who took AstraZeneca is safe, studies say – 13/09/2021

The City of São Paulo will start to apply doses of the Pfizer vaccine to people who have delayed the vaccine schedule against covid-19 due to the lack of immunizing agents from Oxford/AstraZeneca.

The exchange of vaccines, as the exchange between immunizing agents for the application of the second dose is called, was approved by the Ministry of Health and by the PEI (State Immunization Plan) and the State Scientific Committee, in addition to the WHO (World Health Organization) and it was already authorized in specific cases such as pregnant women who received the first dose of AstraZeneca.

But, as with everything related to vaccination against the new coronavirus, it is common to find people afraid to accept this exchange.

Its make bad?

To start with, let’s make it very clear: it is okay to get the Pfizer vaccine if you have taken the first dose of Oxford/AstraZeneca immunizer. There are already studies showing that this exchange is safe for those who will receive the immunizations.

One of them was carried out in the United Kingdom and compared vaccination schedules with the application of two doses of the same vaccine and the mixture between AstraZeneca and Pfizer with an interval of four weeks between doses.

Published in the journal Lancet on January 9 of this year, the study included 830 adults over the age of 50, chosen at random. They received either the Pfizer vaccine or the AstraZeneca vaccine, first one and then the other.

Scientists noted that people who received mixed doses were more likely to develop mild to moderate symptoms with the second dose of the vaccine, including chills, fatigue, fever, headache, joint pain, malaise, muscle and local pain. injection compared to those who received vaccines from the same company.

However, these reactions were short-lived and no other safety issues were noted.

Recently, a Danish study showed that combining AstraZeneca’s vaccine with a second dose of Pfizer’s (or Moderna’s) immunizer provides “good protection”.

Measure is not ideal

Even though it is safe, the exchange between vaccines is not recommended as a standard by experts and should only be authorized in specific cases, such as in Brazil. According to immunologist Gustavo Cabral, columnist for Live well, “the recommended pattern is that whoever takes the first dose of a given vaccine completes the vaccination with the same immunizing agent, so that the expected results are obtained and scientifically proven.”

Marcello Bossois*, the immunologist responsible for the Brazil without Allergy project, explains that, given the need for an exchange, the best thing would be to mix vaccines with the same technologies. In the case of AstraZeneca, it would be Janssen, which is a single dose — both use a “live virus”, such as an adenovirus (which causes the common cold), which has no capacity to replicate in the human body or harm health.

Even faced with the impossibility of this, he agrees that the measure is right at the moment. “Casting the balance of risks and benefits, corroborated with scientific studies already published, this really gives us confidence to do this and end this pandemic soon,” says the immunologist, emphasizing that measures such as these are monitored by the bodies over the months (and years).

But the mix of vaccines is not new. In 2020, in an interview with Live well, Renato Kfouri, infectologist and director of SBIm (Brazilian Society of Immunizations), had already said that starting immunization with a vaccine from a certain laboratory and ending it with a second dose from another is already used in some cases, such as pneumococcal vaccines , from meningitis and whooping cough.

combine can be even better

As much as it is used to make up for the shortage of vaccines, the measure can add an important point in the immunization of people, as explained by Alexandre Zavascki*, head of infectious diseases at Hospital Moinhos de Vento (RS).

“Studies show that the immune response induced by heterologous vaccination — which uses two types of immunizers — is greater than if a person took equal doses of the vaccine — whether Pfizer or AstraZeneca,” he says.

According to intensive care pediatrician Juarez Cunha, president of SBIm (Brazilian Society of Immunizations) in an interview with Lúcia Helena’s Blog, columnist for Live well, there was already the theory that mixing platforms — like Pfizer’s vaccine with AstraZeneca’s — would boost the immune response.

“After all, it’s as if each vaccine acted on one front. One can stimulate more cellular immunity. And another can promote a greater production of antibodies. In fact, the antibodies themselves can bind to different proteins of the virus, depending on the immunizing agent”, says the doctor.

But it is still early to include the CoronaVac vaccine, for example, as there are still no studies done with the immunizing agent. In fact, research will be needed to check the various possibilities of combinations between all the existing vaccines against covid-19.

* interviews made for a report by Luiza Vidal published on 8/14/2021.