A nurse who took part in Pfizer Inc's late-stage coronavirus vaccine trial said she experienced several side effects, leading her to worry she may have contracted the disease.
Kristen Choi, an assistant professor of the School of Nursing at the University of California, Los Angeles, enrolled in the study in August and received two shots of the experimental vaccine, reports the Daily Mail.
However, after the second jab, she had a headache, nausea, chills and even reached a fever of nearly 105F (40.5C) - the highest of her life.
She said that she worried that she may have contracted Covid-19 - and that her friends believed she did. Choi said her symptoms disappeared after 24 hours and said that doctors need to warn patients about the side effects so that "the wrong message doesn't go viral."
In an opinion piece, published in JAMA Internal Medicine on Monday, Choi said she enrolled in phase III of Pfizer's coronavirus vaccine trial after seeing an advertisement on Instagram in early August.
She said the recruitment website was inviting and said volunteering to participate felt like the 'honorable thing to do.'
Within a few days of entering her contact information, she received a call from the study coordinator asking her to take part in the trial.
Because the trial is randomized, considered the gold standard of medical research, Choi didn't know if she would be getting the shot or the placebo.
"I thought about why getting the experimental vaccine rather than the placebo mattered for me as a health care worker - and then, even those stakes seemed low when I thought about what randomization must feel like for patients," she wrote.
"I sent up a final prayer for the active vaccine as the research nurse finally administered the blind-to-me injection."
Choi said she didn't experience any side effects aside from soreness at the site of injection.
She returned one month later for the second of two shots but, this time, she had a much different experience.
"My arm quickly became painful at the injection site, much more than the first time," Choi wrote.
"By the end of the day, I felt light-headed, chilled, nauseous, and had a splitting headache. I went to bed early and fell asleep immediately. Around midnight, I woke up feeling worse - feverish and chilled, nauseated, dizzy, and hardly able to lift my arm from muscle pain at the injection site," she added.
Choi recounted waking up at 5:30am and having a fever of 104.9F (40.5C). After taking acetaminophen and drinking some water, her fever fell over the next few hours to 102F (38.9C).
The next day, she called the research nurse who told her to monitor her symptoms and let the team know if anything changed. Choi's fever was low-grade the rest of the day and by the next morning, the only symptom she was "a sore, swollen bump at the injection site."
According to data from Pfizer's phase I trial, adverse effects are common in adults between ages 18 and 55. A total of 75 percent experienced fatigue, 68 percent had a headache, 33 percent experienced chills, 25 percent reported muscle pain and 17 percent had a fever.
Because of this, Choi believes she received the experimental vaccine
"If this vaccine is approved, it is possible that most people receiving the vaccine could have [one] or more reactions to the vaccine like I did," she wrote.
"Fortunately, my experience of having all symptoms together seems to be rare."