An allergic reaction is the most common adverse event, but the girls also suffer “other unusual events”, and rashes, pain and swelling, fevers, seizures or convulsions, or severe diarrhea.

The extent of the reactions to the vaccine—designed to protect against cervical cancer—has been uncovered by Canadian researchers, who looked at what happened to 195,270 girls who had been given an average of three doses of the vaccine. Of these, 958 needed hospital treatment and 19,321 visited an emergency clinic within 42 days of immunization.

The rates could be higher still, as the researchers were able to track only those cases where the girl went to hospital.

Bizarrely, the researchers from the University of Calgary gave the vaccine a clean bill of health, and considered it safe, because they were looking for cases of venous thromboembolism (VTE)—where dangerous blood clots form—which had been linked to the HPV. Just four of the girls suffered a VTE after they were vaccinated, but three had other health issues that could have caused the problem.