An experimental Covid-19 vaccine being developed by the drug giant Pfizer and the biotech firm BioNTech spurred immune responses in healthy patients, but also caused fever and other side effects, especially at higher doses.
The first clinical data on the vaccine were disclosed Wednesday in a paper released on MedRXiv, a preprint server, meaning it has not yet been peer-reviewed or published in a journal.
The Pfizer study randomly assigned 45 patients to get one of three doses of the vaccine or placebo. Twelve receive a 10 microgram dose, 12 a 30 μg dose, 12 a 100 μg dose, and nine a placebo. The 100 μg dose caused fevers in half of patients; a second dose was not given at that level.
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Following a second injection three weeks later of the other doses, 8.3% of the participants in the 10 μg group and 75% of those in the 30 μg group developed fevers. More than 50% of the patients who received one of those doses reported some kind of adverse event, including fever and sleep disturbances. None of these side effects was deemed serious, meaning they did not result in hospitalization or disability and were not life-threatening.