A man walks past Pfizer’s world headquarters in New York.
Andrew Kelly | Reuters
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clinical data on the vaccine were disclosed Wednesday in a paper released on MedRXiv, a preprint server, meaning it has not yet been peer-reviewed or published in a journal.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.
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.
The vaccine generated antibodies against SARS-CoV-2, the virus that causes Covid-19, and some of these antibodies were neutralizing, meaning that they appear to prevent the virus from functioning. Levels of neutralizing antibodies were 1.8- to 2.8-times the level of that in the recovered patients.
It’s not certain that higher antibody levels will lead to immunity to the virus. To prove that, Pfizer will need to conduct large studies that aim to prove that people who have received the vaccine are at least 50% less likely to become infected. Those studies are expected to begin this summer, mostly in the United States. Pfizer is testing four different versions of the vaccine, but only one will advance to larger studies.
The current study did not include pregnant women, and no other information on the ethnic diversity of participants was noted, although the paper does say that future studies will need to include a more diverse group.
The second dose, a booster shot, was required for immunity. The patients who received the single 100 μg dose had lower antibody levels than those who received two shots of the lower doses.
Fourteen Covid-19 vaccines are currently in human trials, according to the Milken Institute, including entrants from Inovio, CanSino, AstraZeneca, and Moderna. More are expected to start soon, including entrants from Merck, Johnson & Johnson, and Sanofi. In total, 178 vaccines are in various stages of development.
The Pfizer/BioNTech vaccine, like the Moderna vaccine, is based on a technology called messenger RNA, which uses a key genetic messenger found in cells to create protein that the immune system then learns to attack. Moderna has not yet published data on its vaccine but is expected to do so soon.