Mere days after Pfizer announced its new “90% effective” coronavirus vaccine, reports have emerged about “severe” side effects volunteers for the vaccine trial experienced, including fevers and headaches.

According to the British Daily Mail, Carrie, one of the 43,538 participants in Pfizer’s vaccine trial, “said she suffered a headache, fever and aches all over her body, comparable to the flu jab, with the first one. But after the second these became ‘more severe.’”

The Pfizer vaccine will be administered in two doses three weeks apart.

Glenn Deshields, another participant, “said he suffered side effects not dissimilar to a ‘severe hangover.’” The man from Texas said he believes “he received the vaccine because when he had an antibody test with doctors it came back positive.