US investigates potential safety signal with Pfizer Covid boosters
The FDA and the CDC are investigating a “preliminary signal” of whether there might be an increased risk of stroke for people who got Pfizer and BioNTech’s updated Covid-19 vaccine booster.
In a statement posted on the CDC’s website, the agency said its monitoring system for vaccine side effects had been triggered to look for a potential issue with the shots in people ages 65 and older.
The CDC called the findings highly preliminary, and said that “no other safety systems have shown a similar signal and multiple subsequent analyses have not validated this signal.” That included analysis of other large vaccine datasets from Medicare, the United States Department of Veterans Affairs, the companies’ own monitoring programs and a vaccine side-effect reporting collection tool known as VAERS.
That means that it’s possible the warning could end up being statistical noise, or a side effect that’s very rare but enough to trigger an early warning: “Often these safety systems detect signals that could be due to factors other than the vaccine itself,” the CDC said. No such signal was found with Moderna’s updated booster.
Pfizer, in an emailed statement, said it was aware of the government’s report and that its own data showed lower rates of strokes following vaccination in patients who had been vaccinated, compared with typical rates of stroke. “Vaccine safety remains of utmost priority for Pfizer and BioNTech,” the company said.
Any vaccine carries some level of risk or side effect, though typically far smaller than the consequences of diseases they are meant to guard against.
The CDC said it wasn’t making any changes to its vaccine recommendations at this time. According to data collected by the agency, 69% of the US population has completed the original vaccine series, and 16% — about 50 million people — have received the updated booster.
The shots remain very effective in preventing hospitalization or death from Covid-19. Unvaccinated people are about six times more likely to die from the disease than are vaccinated people, according to ongoing surveillance data collected by the agency. That gap grows substantially when comparing unvaccinated people to those who have received the updated booster dose. The US continues to report more than 2,000 Covid-related deaths a week.
Vaccine risk tracking
The CDC identified the safety signal through its vaccine-safety datalink system, or VSD, which it calls a “near real-time” monitoring system. The system triggered an investigation to look at whether people 65 and over who got Pfizer’s booster were more likely to have a stroke in the 21 days after getting the shot than in days 22 to 42 after vaccination.
“Although the totality of the data currently suggests that it is very unlikely that the signal in VSD represents a true clinical risk, we believe it is important to share this information with the public,” the CDC said in its statement.
The safety signal was specific to Pfizer’s updated bivalent vaccine, which targets two different strains of the coronavirus and was rolled out last year. The original and updated vaccine are huge sellers for Pfizer and its partner BioNTech.
The agencies didn’t share the specific rate or the number of stroke cases that they are investigating. The data will be up for discussion at the FDA’s Vaccines and Related Biological Products Advisory Committee meeting on Jan. 26.
In 2020, when Johnson & Johnson’s vaccine was first rolled out to the public, reports came back of clots and strokes in a handful of people who had received it.
A review of the J&J vaccine side effects, published in the Annals of Internal Medicine, found 3.83 cases per million doses of the J&J shots developed blood clots and low platelet counts during the December 2020 to August 2021 period. The cases were more common in women, and about 15% of hospitalized cases were fatal. The review also looked at the Pfizer and Moderna mRNA vaccines in use at the time, and found the rates were far lower — 0.00855 cases per million doses.
The side effects of the J&J vaccine, while relatively rare, were widely covered by the media at the time and contributed to a drop in use of the company’s shots.
