Third vaccine dose safe for high-risk patients

Giving a third full dose of an mRNA vaccine to people with medical conditions that impair their immune system’s response to the usual two-shot regimen appears to be safe in terms of side effects, new data show.

Immunocompromised individuals have been advised by medical authorities to get a third full dose as a booster. While studies have generally shown improved antibody levels after the third dose, data on side effects have been limited. For a report posted on Tuesday on medRxiv ahead of peer review, researchers at the Mayo Clinic in Rochester, Minnesota reviewed electronic health records of nearly 48,000 people who received three full doses of either the Moderna or Pfizer/BioNTech vaccine.

There were slightly higher rates of fatigue, nausea, headache, joint and muscle aches, stomach upset, and chills after the third dose than after the second shot. But “reporting of severe adverse events remained low” after the third dose, with rates at or below 0.01%, the researchers said.