COVID-19 vaccines that are given at the same time as a flu vaccine do not cause significantly worse reactions.
A British study published by the Social Science Research Network found no sign of risk in getting an influenza vaccine and the second dose of a COVID-19 vaccine (AstraZeneca or Pfizer-BioNTech) at the same time. The study consisted of 679 volunteers from April to June 2021 at 12 sites across Britain. All of the volunteers had taken the first dose of a COVID-19 vaccine, either of AstraZeneca or Pfizer; half of them were given a flu shot and the other half a placebo. Jabs were given in opposite arms on the same day. Later, they were monitored for side effects. However, the researchers did not find that any sequence of a flu vaccine and COVID-19 vaccine resulted in worse reactions.
When looking at the safety of both vaccines, the researchers also measured antibodies to the coronavirus in the volunteers. The study then interpreted that concomitant drugs preserve the immune response to both vaccines.
According to the Washington Post, William Schaffner, medical director of the National Foundation for Infectious Diseases, said "'it's terribly important' to get both the flu and coronavirus vaccines." Kelly Moore, president and CEO of the Immunization Action Coalition, also advised to take both the vaccines as COVID-19 and flu vaccines "train your immune system to protect you against completely different viruses" and further stated that "getting one-shot that protects you against one virus will not offer any protection against the other."
According to the Centers for Disease Control and Prevention, "one can get a COVID-19 vaccine and any other vaccines, including a flu vaccine, at the same visit" and further mentioned that the vaccine's potential side effects "are generally the same when given alone or with other vaccines." Moreover, the COVID-19 vaccines were approved with an abundance of caution.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19, including symptoms, prevention, and available treatment, please refer to the World Health Organization or your national healthcare authority.