The reports of side effects caused by the vaccine, which has so far proven safe, comes days after Pfizer and its German partner BioNTech announced the vaccination was 90 per cent effective in preventing coronavirus, with the drug companies expected to seek US emergency use authorisation this month.
During the trials, the more than 43,500 volunteers from six countries were not informed whether they received the vaccine or a placebo.
However, some volunteers reportedly said they were able to tell they had received the vaccine because of certain side effects such as headaches and muscle aches.
According to Glenn Deshields, 44, from Austin, Texas, who spoke to the Press Association, his side effects were similar to a “severe hangover,” but cleared up quickly.
An antibody test taken by Deshields later revealed he had developed antibodies to the virus, convincing him that he had received the real vaccine.
Another volunteer, a 45-year-old woman from Missouri identified as Carrie, said she experienced fever, a headache and body aches after she received her first injection, which she compared to those of a flu injection, with the flu-like side effects reportedly worse after she received her second injection.
In a statement Monday regarding the effectiveness of the vaccine, Dr Albert Bourla, Pfizer Chairman and CEO said: “Today is a great day for science and humanity. The first set of results from our Phase 3 Covid-19 vaccine trial provides the initial evidence of our vaccine’s ability to prevent Covid-19.
“We are reaching this critical milestone in our vaccine development program at a time when the world needs it most with infection rates setting new records, hospitals nearing over-capacity and economies struggling to reopen. With today’s news, we are a significant step closer to providing people around the world with a much-needed breakthrough to help bring an end to this global health crisis. We look forward to sharing additional efficacy and safety data generated from thousands of participants in the coming weeks.”
As of now, there are still lingering questions about how effective the vaccine is by age and ethnicity, and how long immunity may last, Reuters reports.