Study: Side effects seen more often when mixing COVID-19 vaccines

A U.K. study published Wednesday reported that side effects to the coronavirus vaccine were seen more often when mixing ones from different makers.

The study, published by The Lancet, had participants take the two vaccine doses needed to become fully vaccinated using two different vaccines — one from Pfizer and BioNTech, and one developed by AstraZeneca and Oxford University — instead of two doses of the same vaccine, as is typical.

The findings showed that increased side effects, including pain, fatigue and chills, consistently went up each time the vaccines were mixed. 

It is a “really intriguing finding, and not something necessarily we were expecting to see such a consistency on,” said Matthew Snape, lead investigator for the trial, Politico reported.

The side effects, despite being reported more often and in greater severity, still did not last long, and reportedly no one had to be hospitalized due to them. 

The initial trial is expanding to included Moderna and Novavax vaccines, along with testing at 12-week intervals instead of four-week ones.

Mixing of the two-shot Pfizer and Moderna vaccines has been approved in the U.S., but only under “exceptional situations.” 

The Novavax and AstraZeneca vaccines are not approved for use in the U.S.

Snape said there has been international interest in these findings, and he has shared the data with groups across the world.