Dr. Moncef Slaoui, the leader of the Trump administration’s vaccine program for COVID-19 called Operation Warp Speed, said that both Pfizer and Moderna’s drugs are safe but produced noticeable side effects in 10% to 15 % of people who received the vaccine in clinical trials.

According to CNBC, those who did suffer side effects reported redness and pain at the infection site along with fever, chills, muscle aches and headaches.

“The longer, more important kind of adverse events such as autoimmune disease or others have not been reported in a different way between the placebo group and the vaccine group in these two trials, which is very reassuring, ” Slaoui said.

According to the New York Post, although the volunteers who took part in the phase 3 trials weren’t told if they were injected with the vaccine or a placebo, the participants who experienced flu-like side effects such as muscle aches, fever and headaches assumed they got the drug.

One volunteer, 45-year-old Carrie from Missouri, said she experienced a headache, fever and body aches, after her first shot in September. Giving only her first name, she told The Sun that her side effects were more severe after her second dose last month. Carrie believes that she received the actual vaccine based on her experiences.

Glenn Deshields, 44, from Austin, Texas, suffered “severe hangover” symptoms that fortunately soon cleared. A post-vaccine antibody test that came back positive confirmed his suspicion that he did receive the vaccine and not the placebo, according to the Post.

Slaoui said that side effects can last up to a day and a half, according to CNBC.

According to NPR, The FDA’s Vaccines and Related Biological Products Advisory Committee will review the new findings along with previous information on the safety and side effects of the vaccines before granting emergency approval in the next few weeks. The Pfizer drug is up for review December 10 in an open session that includes the general public. The agency says it will not cut corners to ensure the welfare of the millions anticipated to receive the vaccines.

Dr. Carlos del Rio, of the Emory Vaccine Center at Emory University, who was involved in testing the Moderna vaccine, said the side effects from the drug were similar to those triggered by the shingles vaccine.

“You feel terrible for a day or two but then you’re fine,” he said, according to NPR, adding that the discomfort is a small price to pay to have protection from a potentially deadly disease. “We’re going to have to do very good messaging to people this is not COVID-19, it’s a side effect of the vaccine and it’s OK to have it,” he said. “It actually means the vaccine is working.”