Combining two different coronavirus vaccines multiplies adverse reactions

Fever, muscle aches, and general fatigue. Three of the possible adverse reactions to the application of vaccines against covid-19 they triple in cases in which the first and second doses of different formulations are alternated, according to the first results of a study published in The Lancet, although these effects are not serious and can be controlled with paracetamol.

The study was conducted, in particular, with the combination of the drugs from Pfizer and AstraZeneca, while the control groups received the two doses from the same laboratory. Despite the adverse reactions, the researchers emphasize that if the creation of antibodies is not affected, it could accelerate the advance of immunization. The conclusions of the work on the efficacy or safety will not be ready until June.

After several European countries questioned the continuity of the applications with the Oxford-AstraZeneca vaccine due to the appearance of a dozen cases of thrombosis, in the United Kingdom this investigation was initiated to test what happened in case of alternating different formulations between the first and second applications. Preliminary results indicate that, although they indicated that adverse reactions may increase, the effects are not severe, are short-lived, and are relieved with paracetamol.

The still-ongoing trial published by The Lancet called Com-Cov began last February, led by Oxford University researcher Matthew Snape. “If we can show that these combination plans generate an immune response that is as good as normal strategies and without a significant increase in reactions to the vaccine. It would allow more people to complete their covid immunization in less time.”

The research involved 830 volunteers, over 50 years of age, and the period between the first and second dose was decided to defer it to 84 days for almost half of the study participants, so that in the next few days the application will advance for part of the group under study. Results published Wednesday by The Lancet show reactogenicity figures in the other half of the group of volunteers, who received the second dose 28 days after the first application.

Among the preliminary results of the study, it was shown that the increase in adverse reactions increased after the first application for those who received the AstraZeneca vaccine in both applications -only 10 percent had side effects-, while with the Pfizer increases with the second dose.

But those who were inoculated, first alternating the AstraZeneca formula and then the Pfizer formula, showed a greater increase in adverse reactions, which reached 34 percent of the cases, in no case serious. For those who received the Pfizer dose followed by AstraZeneca, the increase in side effects rose to 41 percent, versus 21 percent for those who received Pfizer both times..

“The results suggest that plans to mix doses could cause an increase in missed work the day after immunization,” said the investigator in charge, adding that they did not find serious safety problems, such as thrombi or serious allergies, although did not rule out that they could appear in patients younger than the sample population.


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