Spanish trial results on mixing AstraZeneca and Pfizer doses: generates more antibodies and mild side effects

Strong immune response and mild to moderate side effects in people under 60 years of age, this is the summary of the results of the Spanish CombiVacs trial, launched by the Carlos III Health Institute (ISCIII), that evaluates the convenience of mixing vaccines from different manufacturers.

Exactly, what was measured were the results of putting a dose of Pfizer after having already received one of AstraZenca, in order to remove from limbo all the people who are still waiting for their second dose of AstraZeneca and who had been delayed due to the appearance of rare cases of thrombi.

Greater protection than with the same manufacturer

The trial involved 676 patients from different age groups and regions of Spain who received a single dose of AstraZeneca, ranging from 18 to 59 years old, who were divided into two groups: one of 226 who received the dose “immediately” and another 450 who received it after 28 days. The results presented this Tuesday are those analyzed 14 days after receiving the dose from Pfizer.

In addition, the protection provided by a second Pfizer puncture is even greater than if it is repeated with the same vaccine: neutralizing antibodies, those that protect the body against the coronavirus, would be multiplied by seven, while two doses of the same drug offer only three times more protection, that is, very mild side effects.

Thus, the preliminary results of the CombiVacs appear to be very similar to the preliminary results of the British equivalent, the Com-Cov trial.

With these results, the Ministry of Health must now make a decision about which vaccine to administer to those under 60 years of age who stayed with the first dose of AstraZeneca, a group of almost two million people and made up of risk professionals and teachers.

However, the experts who advise the Ministry have advanced in an interview that they will probably choose to administer a dose from the same manufacturer, that is, AstraZeneca. “Today’s results support being able to vaccinate patients who have received the first dose of AstraZeneca, but the decision does not correspond to the researchers of this study,” according to Jesús Antonio Frías, coordinator of the ISCIII Clinical Research Network.