COVID Vaccine Side Effects Include High Fever, Body Aches and Bad Headaches, Experts Say

As the world inches closer to effective COVID-19 vaccines becoming available, public health experts are warning that people should be prepared for the possibility that they could experience severe, but ultimately unharmful, side effects after being given the vaccines.

Vaccines from Moderna and Pfizer, both given in two doses approximately one month apart, could soon be approved for public use after data released from clinical trials showed that they may be up to 95 percent effective in providing immunity against the virus. While neither vaccine is believed to come with significant life-threatening side effects, experts are warning that those who receive the vaccines should be ready for unpleasant but temporary reactions.

"We really need to make patients aware that this is not going to be a walk in the park," Dr. Sandra Fryhofer of the American Medical Association said during a recent meeting of a group of experts who advise the Centers for Disease Control and Prevention (CDC) on vaccines, according to a Monday report from CNBC.

"They are going to know they had a vaccine," Fryhofer added. "They are probably not going to feel wonderful. But they've got to come back for that second dose."

In the Moderna vaccine trials, the only common "severe" side effect seen after the first dose was pain at the injection site, occurring in 2.7 percent of patients. After the second dose, the most common severe side effect was fatigue, which was seen in 9.7 percent of participants. Muscle aches or pains were experienced by 8.9 percent, while 5.2 had joint pain. Another 4.5 percent had headaches and 4.1 percent experienced pain at the injection site.

Luke Hutchison, a 43-year-old computational biologist who participated in the Moderna trials, told Science magazine that he endured an "unbearable" 102 degree fever after getting an injection of what he assumes was the vaccine, although he can't be certain because participants do not know whether they received a placebo instead.

"I started shaking. I had cold and hot rushes... I was sitting by the phone all night long thinking: 'Should I call 911?'" Hutchison said of his symptoms, which were gone after about 12 hours. "Nobody prepared me for the severity of this."

Pfizer/BioNTech COVID-19 Vaccine
A COVID-19 vaccine from Pfizer/BioNTech is one of several that could soon be available to the public following promising clinical trial data, although experts are urging the public to be prepared to experience temporary, but potentially severe, side effects after being vaccinated. JOEL SAGET/AFP/Getty

All vaccines come with a list of possible side effects, including rare but serious side effects. However, experts have long stressed that with modern vaccines it is not possible to contract the pathogen that one is being vaccinated against by taking the vaccine itself, while any side effects that do occur are nearly always short-lived and far less serious than the disease it provides protection against, even if they are unpleasant.

Detailed safety data from late stage trials of Pfizer's vaccine, developed in collaboration with the German company BioNTech, has not yet been released, but the companies said the vaccine does not present "any serious safety concerns." Initial data showed that fatigue and headaches were the most common side effects, both occurring in fewer than 4 percent of trial participants after the second dose.

Since both vaccines have the potential to result in severe but temporary side effects, possibly more often than other common vaccines like flu shots, some experts have urged doctors and public health officials to inform the public that effects like a temporary but high fever are possible, while taking care to counter those who would use the ultimately harmless side effects to promote anti-vaccination conspiracy theories.

"Public health professionals are going to have to have a story that gets out in front of [stories like Hutchison's]—that responds to the way that people are going to try to make that a story about vaccine injury," Bernice Hausman, a vaccine controversy expert at the Pennsylvania State University College of Medicine, told Science.

Newsweek reached out to CDC for comment.