What do we know about the covid-19 vaccine mix for the booster dose?

(CNN) — The US Food and Drug Administration (FDA) is discussing the option of allowing Americans to may receive a different booster dose of the coronavirus vaccine to the first doses they received in principle.

So far the FDA has only authorized the booster dose of Pfizer’s COVID-19 vaccine for some adults. It is currently considering the authorization of boosters for the Moderna and Johnson & Johnson vaccines.

This is the most effective vaccine against covid-19 in the United States. 0:43

What is known about the covid-19 vaccine mix?

So far there is no official recommendation on mixing covid-19 vaccines, but a preliminary study suggests that there are no side effects when mixing vaccine types, especially Pfizer and Moderna vaccines, which use the same technology from MRNA.

Ahead of FDA experts meeting this week to determine whether or not to mix booster doses, the National Institutes of Health (NIH) presented FDA vaccine advisers with early information on an ongoing study showing that it doesn’t matter which vaccine people got first and which booster they got. According to this study, it is safe to mix vaccines for boosters and the immune system response was accelerated.

Boosters with mixed vaccines also gave a good response to the delta variant.

While there are still no extensive scientific studies on the mixture of vaccines or its side effects, Dr. Elmer Huerta, public health expert and contributor to CNN en Español, he said on his podcast “Reality Vs. Fiction” that making this decision without consulting a doctor should be seen as a form of self-medication. This especially if vaccines are combined to comply with a procedure to be able to enter certain countries, or if there is distrust of the previously received vaccine.

“Revaccination for immigration reasons and being able to enter the United States or Europe, or due to distrust of the vaccines received, there are no scientific studies in this regard … they should be considered as forms of self-medication not supported by scientific studies, and they should only be done with the authorization of a doctor, “said Huerta.

“However, combining vaccines to complete an interrupted vaccination schedule is undoubtedly a medical necessity, since it implies obtaining – with the second dose of another vaccine – the protection that was interrupted after receiving the first interrupted dose,” he added. Vegetable plot.

USA: recommend booster doses of J&J vaccine 3:21

Is there a better combination of vaccines than others?

Huerta cited studies done in Germany, Spain and the United Kingdom that have determined that the first dose of AstraZeneca can be completed with a second dose of the Pfizer and Moderna vaccines.

“Those studies were prompted by the suspension of the AstraZeneca vaccine in Europe earlier this year,” Huerta said.

Another combination studied to complete a vaccination schedule, according to Huerta, is the one that interchanges the Pfizer and Moderna vaccines, a combination allowed in Canada, but which in the United States, the CDC recommends only in exceptional situations.

A third combination that has been studied, cited by Huerta, is one that allows the completion of the vaccination schedule that began with the Russian Sputnik V vaccine —which is not authorized in the United States, but is authorized in some Latin American countries— with a dose of AstraZeneca and Moderna. This study was done in Argentina due to the shortage of the second dose of Sputnik V, Huerta said.

The Chilean government concluded – based on a study not yet published in a scientific journal – that it is possible to reinforce the two doses of the Sinovac vaccine with one from AstraZeneca or Pfizer, while the Uruguayan government approved the reinforcement of Sinovac with a single dose. from Pfizer.

In the Dominican Republic, a booster dose with the AstraZeneca and Pfizer vaccines has been approved, the same as in Peru, whose Minister of Health reported that those who have received two doses of the Sinopharm vaccine may receive a booster dose with some of those two vaccines.

Now, the FDA may approve a booster dose of mRNA vaccines (Pfizer or Moderna) for people who received a J&J vaccine.

USA: Recommend third booster dose of Moderna 3:41

“There should be no preference for mixing certain vaccines”

Last week, the FDA asked members of the Vaccines and Related Biologicals Advisory Committee (VRBPAC) to comment on the possibility of mixing vaccines to implement possible drafting changes in emergency use authorizations for the three vaccines licensed in the US: Moderna, Pfizer and J&J.

VRBPAC member Dr. Amanda Cohn, who is also medical director for the National Center for Immunizations and Respiratory Diseases at the US Centers for Disease Control and Prevention, said she would help CDC guide the use reinforcements.

“I don’t think there is any kind of need from a public health perspective to have a preference for mixing or matching certain vaccines,” Cohn said at the meeting.

“But I think from a public health perspective there is a clear need in some situations for people to get a different vaccine. For example, the doses of J&J, for the 14 million people who have been vaccinated, many of those people may not have access to a second dose of J&J. So if there is no language allowed in the FDA data sheets or emergency use authorization, those people are left behind, “he said.

In addition, he noted, there is a rare side effect of blood clotting known as thrombosis with thrombocytopenia syndrome, or TTS, which is more common in young women and is associated with the J&J vaccine.

“The same is true if a person is a 30-year-old woman who may feel that she is now at risk for a reaction after receiving a first dose of J&J before TTS was recognized, so it can be allowed, for example That woman get a different type of vaccine, ”Cohn said.

“And conversely, it allows, for example, in nursing homes where the majority of residents received mRNA vaccines, for a pharmacy to enter a nursing home and only have one booster vaccine product for people who received Modern or Pfizer. “

Therefore, if a nursing home resident receives their first two doses with the Pfizer or Moderna vaccine, it would be fine to receive a booster with a different brand.

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