COVID-19: Mixing AstraZeneca and Pfizer Vaccines is Safe and Effective Study Shows

A first dose of the AstraZeneca and a second from Pfizer would be “safe and effective” and would even produce more antibodies than giving the same vaccine in both injections.AstraZeneca COVID-19 Vaccine

Mixing vaccines does not seem to be a problem and would even be “safe and effective,” according to the results of a study conducted in Spain. In preliminary results presented recently and also shared by the scientific journal Nature, the Institute of Health Carlos III (ISCIII), which depends on the Spanish Ministry of Health, and wants to reassure the two million Spaniards who may get a combination of vaccines. “Those who have received a first dose of AstraZeneca can safely and effectively receive as a second dose the Pfizer vaccine,” said Jesús Antonio Frías, who coordinated the Combivacs study, which examined the combined administration of the AstraZeneca and Pfizer vaccines.

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More neutralizing antibodies

In France, another country considering the combination approach, people younger than 55 who received the first dose from AstraZeneca can receive a different vaccine for their second dose. For these patients, the second dose should contain a messenger RNA vaccine, Pfizer or Moderna. This recommendation by the French health authority is dated April 9 and follows reports of thrombosis in several individuals. The use of AstraZeneca’s vaccine was suspended for some time before it was reauthorized again for people over 55. Meanwhile, more than 500,000 patients under 55 who received the AstraZeneca vaccine as a first dose must now receive a second dose from Pfizer or Moderna.

For this study, the researchers compared the immune response of 600 patients. Of these, 442 received Pfizer as a second injection after the first with AstraZeneca, and 221 received only the first dose. The vaccine cocktail of the first group produced a “very satisfactory” antibody count 14 days after the second injection, the researchers said. “In terms of baseline levels, after the second dose of Pfizer, the antibody titer (the number of antibodies) IgG increases up to 150-fold and that of the neutralizing antibodies about seven-fold,” noted Teresa Pérez, coordinator of the serology laboratory at the Carlos III Health Institute.

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No serious side effects

Although this study did not compare vaccination with two doses of the same vaccine, the researchers believe that the results show a better immune response after combining the two vaccines. The level of antibodies “is higher than what is found in the literature,” says José Alcamí, a researcher at ISCIII, showing that the number of neutralizing antibodies increases about three times with the second dose from AstraZeneca and five or six times with the double dose from Pfizer.

No side effects requiring additional medical treatment or hospitalization occurred. Pain at the site of injection (88.2%) was the most commonly reported side effect. About half of the participants experienced headaches (44.4%) and general malaise (41.7%), and in very rare cases, only (2.7%), fever occurred. But almost all symptoms had disappeared by the third day after injection. “The data are very similar to those of the Pfizer study,” noted Magdalena Campins, head of the epidemiology department and coordinator of the study at Vall D’Hebron Hospital in Barcelona.

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Results of the previous study confirmed

These results confirm those of a British study whose data were published a few days earlier in the journal The Lancet. This study showed an increase in mild and moderate reactions without serious safety concerns after combining the vaccines. In addition, the results showed that symptoms did not persist and disappeared within 48 hours. “There were no hospitalizations due to triggered symptoms, and most of this increase in reactogenicity (excessive immunological response to a vaccine, ed.) was observed within 48 hours of immunization,” the researchers said.

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