Last week, the Advisory Committee of Vaccines and Related Biological Products of the United States FDA authorized a third booster dose for Moderna’s vaccine, and a second booster for the Janssen (Johnson & Johnson) vaccine, which – like the one recommended for the Pfizer– may be administered to people over 65 years of age, to people between 18 and 64 years of age with comorbidities that predispose them to complications if they contract COVID-19, and workers exposed to the contagion (including health workers).
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In addition, the FDA also discussed the possibility of mixing vaccines, an issue that had remained pending when the J&J vaccine booster was discussed. That because one prepublication, released two days before the expert meeting, showed that the booster of this vaccine with Pfizer or Moderna arouses a greater production of antibodies than that produced with a booster of the same vaccine.
The clinical study consisted of administering a booster dose to a group of 458 people, divided into three groups of approximately 150 people each, who had been fully vaccinated with Pfizer, Moderna and J&J.
The groups were then divided into three groups of 50 people, each of whom received a booster with the same vaccine (homologous vaccination) or with different vaccines (heterologous vaccination). In each group, the neutralizing antibodies produced by these booster doses were measured, and then nine groups were evaluated.
The results indicated that the highest neutralizing antibody titers were obtained with homologous vaccinations of vaccines messenger RNA, that is, Modern with Modern, and Pfizer with Pfizer.
“The results open the doors […] that allow mixing vaccines from different technological platforms ”.
The most interesting results occurred in the group that was initially vaccinated with J&J, since it was shown that the volunteers who received the same Johnson & Johnson vaccine as a booster increased their level of neutralizing antibodies four times, while if they received a booster from Pfizer, they increased it 35 times and 76 times if they received a booster from Moderna.
That is why, although the committee approved that people vaccinated with J&J receive a booster of their same vaccine, the possibility remains – as expressed by the FDA’s director of vaccines, Peter Marks – that the booster doses of the J&J vaccine could be messenger RNA.
These results also open the doors of future research that allows mixing and combining vaccines from different technological platforms, with the aim of improving the production of antibodies in vaccinated people.
Aside from recent decisions by the FDA to authorize booster doses for vaccines used in that country (Pfizer, Moderna and J&J), there are already decisions to use booster doses in other countries.
Government Chilean concluded – on the basis of a study not yet published in a scientific journal – that it is possible to reinforce the two doses of vaccine CoronaVac from Sinovac, with one from AstraZeneca or Pfizer; while the government Uruguayan approved the booster for the same vaccine, with one from Pfizer.
On Dominican Republic a booster dose has been approved with the AstraZeneca and Pfizer vaccines.
This is in addition to the recent decision of the Minsa in Peru, which authorized that the front-line personnel who received two doses of the vaccine Sinopharm may receive a booster dose with the Pfizer or AstraZeneca vaccines.
—Reasons to mix—
Apart from mixing vaccines to reinforce complete vaccination schedules, there are three other reasons why many people want to combine vaccines: the need to complete an interrupted vaccination schedule after having received the first dose, distrust of previously received vaccines and the fulfillment of immigration procedures to enter the US or Europe. These last two imply a revaccination of the person.
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 dose.
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In this regard, studies carried out in Germany, Spain and the United Kingdom have determined that the first dose of AstraZeneca can be completed with a second dose of the vaccines from Pfizer and Moderna. Those studies were prompted by the discontinuation of the AstraZeneca vaccine in Europe earlier this year.
Another combination studied to complete a vaccination schedule is the one that interchanges the Pfizer and Moderna vaccines, a combination allowed in Canada, but which in the US the Centers for Disease Prevention and Control (CDC) recommends only in exceptional situations.
The third combination studied to complete an interrupted vaccination schedule is the one that allows completing the vaccination started with the vaccine Sputnik V with a second dose of AstraZeneca or Moderna. This study was done in Argentina due to the shortage of the second dose of Sputnik V.
With respect to the last two, which imply revaccination due to mistrust of the vaccines received or for immigration reasons, There are no scientific studies on this, so the risk of getting vaccinated a second time should be considered as a form of self-medication, not supported by scientific studies, and must be done under the person’s own responsibility and with prior authorization from a doctor.
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