Simultaneous vaccination against covid and flu is safe, study shows

BMJ 2021 ; 375 doi: https : //doi.org/10.1136/bmj.n2411 (published October 1, 2021)

Commentary

In this study, when the influenza vaccine is given at the same time as the second dose of covid-19 vaccine, the immune response is maintained and there are no concerns about safety.

※The study, funded by the National Institutes of Health, is available as a preprint and has not yet been peer-reviewed.

A total of 679 volunteers were recruited from 12 NHS sites in England and Wales, all over the age of 18, all of whom had already received one dose of either Pfizer-BioNutech or Oxford-AstraZeneca vaccine and were awaiting a second dose.

Two covid vaccines and three flu vaccines were tested, yielding a total of six combinations.

Volunteers were randomly assigned to receive either the flu vaccine or a placebo saline injection in the arm opposite the second covid-19 vaccine.

Three weeks later, the group that had received the placebo was given the flu vaccine and vice versa. The participants also attended a third study visit to discuss the side effects they experienced and to provide blood samples.

The primary endpoint was one or more systemic reactions reported within 7 days of the first study vaccination, with a difference of less than 25% considered acceptable.

The most common adverse reactions were pain and malaise around the injection site.

No significant differences were found in four of the six group combinations, and in two combinations there was a slight increase in the number of reports of at least one adverse reaction when both covid-19 and the influenza vaccine were used together, but the reactions were mostly mild or moderate.

The study also found that immune responses to both the flu vaccine and the covid-19 vaccine were maintained when they were given together.