COVID-19 vaccine: Fever, headache are normal side effects, experts say

The Food and Drug Administration has issued emergency use authorization for the COVID-19 vaccine for people 16 and older. As a result, the Pfizer-BioNTech COVID-19 vaccine will be distributed in the U.S.

“The FDA’s authorization for emergency use of the first COVID-19 vaccine is a significant milestone in battling this devastating pandemic that has affected so many families in the United States and around the world,” FDA commissioner Dr. Stephen M. Hahn, said in a press release on Friday. “Today’s action follows an open and transparent review process that included input from independent scientific and public health experts and a thorough evaluation by the agency’s career scientists to ensure this vaccine met FDA’s rigorous, scientific standards for safety, effectiveness, and manufacturing quality needed to support emergency use authorization. The tireless work to develop a new vaccine to prevent this novel, serious, and life-threatening disease in an expedited timeframe after its emergence is a true testament to scientific innovation and public-private collaboration worldwide.”

Dr. Peter Marks, the director of the FDA’s Center for Biologics Evaluation and Research added, “With science guiding our decision-making, the available safety and effectiveness data support the authorization of the Pfizer-BioNTech COVID-19 Vaccine because the vaccine’s known and potential benefits clearly outweigh its known and potential risks. The data provided by the sponsor have met the FDA’s expectations as conveyed in our June and October guidance documents. Efforts to speed vaccine development have not sacrificed scientific standards or the integrity of our vaccine evaluation process. The FDA’s review process also included public and independent review from members of the agency’s Vaccines and Related Biological Products Advisory Committee. Today’s achievement is ultimately a testament to the commitment of our career scientists and physicians, who worked tirelessly to thoroughly evaluate the data and information for this vaccine.”

Shown to be more than 90 percent effective in phase III clinical trials, the vaccine has been vetted by an independent panel of experts who found no significant side effects and deemed it safe for the general public.

But as the rollout of the vaccine begins, experts are cautioning about a potential set of reactions that some may experience after getting the shot — including fever, fatigue and muscle aches. All reactions in the Pfizer trial were characterized as mild or moderate, and reportedly resolved within a few days. And the reactions, experts say, are not only normal, but signs that the vaccine is performing its desired goal.

In an earlier interview with Yahoo Life, Dr. Florian Krammer, a renowned professor of vaccinology at the Icahn School of Medicine at Mount Sinai, explained why. “You may get elevated temperature, headache or muscle aches. What happens there is that your innate immune system recognizes that there's something in your body that doesn't belong there and sounds the alarm,” Krammer said. “If you feel sick, it’s not because a virus is infecting you, it’s because the vaccine is triggering [an immune response].”

Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security, agrees. “Fever is a normal side effect of vaccination and is something to expect after you get this vaccine,” Adalja, who may be getting the vaccine as soon as next week, tells Yahoo Life. “It is a sign of the immune system reacting to the vaccines, so it’s a sign that the vaccine is performing its intended function.”

The other concern many have expressed is the potential for an allergic reaction, which two individuals in the U.K. have reportedly experienced. But Adalja points out allergies to vaccines are very rare, and that both those who experienced this reaction in the U.K. were high risk. “These are individuals who had a history of severe allergic reactions to the degree that they were prescribed EpiPens,” says Adalja. “And so thus far, this isn't something that people need to worry about — outside of those individuals who carry around EpiPens or who have severe allergies to foods, to other vaccines or to medications.” (A reported 3.6 million Americans carry EpiPens, according to a 2016 report by the Wall Street Journal.)

The FDA plans to move forward with approval of the Pfizer COVID-19 vaccine. Here's what you need to know about the potential reaction. (Photo: Getty Images)
The FDA plans to move forward with approval of the Pfizer COVID-19 vaccine. Here's what you need to know about the potential side effects. (Photo: Getty Images)

To be sure, the majority of those who receive the vaccine will likely have few if any side effects. In Pfizer’s trial data, the only two side effects experienced in more than 2 percent of study participants were fatigue, and headache. An even smaller number of participants developed muscle aches or fever. But that’s not to say they can’t occur. In an editorial published by JAMA Internal Medicine, nursing researcher Kristen R. Choi said that she experienced a reaction after getting the second dose of the Pfizer vaccine. Choi has not yet been informed whether she received a placebo or the real vaccine, but assumes the latter.

“I took my temperature and looked at the reading: 104.9 degrees Fahrenheit. This was the highest fever I can ever remember having, and it scared me. I took acetaminophen and drank a glass of water. When the [Pfizer] research office opened at 9 a.m., I called to report my reaction to the injection,” Choi writes. “Thankfully, my fever had come down to 102 degrees Fahrenheit by then. The research nurse said, ‘A lot of people have reactions after the second injection. Keep monitoring your symptoms and call us if anything changes.’ My fever hovered around 99.5 degrees Fahrenheit for the rest of the day. By the next morning, all my symptoms were gone except a sore, swollen bump at the injection site.”

Although a medical professional herself, Choi says she was caught off guard by the symptoms, and even had a fleeting thought that it might be COVID-19. Adalja emphasizes that this outcome isn’t possible. “It is impossible to get COVID-19 from the Pfizer vaccine because the Pfizer vaccine only contains a gene for the virus,” says Adalja. “You cannot get the whole SARS-CoV-2 virus from something that doesn't include the whole SARS-CoV-2 virus.”

Choi is now hoping to inform others that this reaction may happen, and that if it does, it is normal.

“Despite the extensive information I had on the research process and vaccine, on a personal level I did not get the message that I should anticipate [an immune] response,” writes Choi, adding at the end, “every physician and nurse in the U.S. needs to be prepared to have a conversation about adverse effects with patients.”

For the latest coronavirus news and updates, follow along at According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.

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