No new blood clots have been reported after the United Kingdom restricted the use of AstraZeneca’s coronavirus vaccine for people under the age of 40.
Reuters reported Wednesday that a study published by The New England Journal of Medicine looked at the incidence of vaccine-induced immune thrombocytopenia and thrombosis (VITT), a rare blood clotting disorder that has been labeled a side effect of the vaccine.
Sue Pavord, a consultant hematologist who led the study, told reporters that the side effect usually affects younger people who were otherwise healthy, Reuters reported.
But she said an initial spike of cases of the incident have subsided since Britain decided in May to only offer the vaccine to those over the age of 40.
“We haven’t seen new cases for the last four weeks or so and this has been a tremendous relief,” Pavord said, according to Reuters.
People under the age of 40 in the U.K. will usually be offered mRNA vaccines manufactured by either Pfizer of Moderna.
The study, published Wednesday, looked at 294 hospital patients in the U.K. who were suspected to have VITT between March 22 and June 6.
All the patients, who were between the ages of 18 and 79, were hospitalized within five to 30 days after receiving their first vaccine dose.
By the end of the study, about 16 million first doses of the AstraZeneca vaccine had been administered to people over the age of 50, and 8 million first doses were administered to those under age 50.
The study found that the incidence of VITT in people under the age of 50 was at least 1 in 50,000 among patients, and for those over the age of 50 was 1 in 100,000.
The blood clotting issue has also been labeled as a rare side effect of Johnson & Johnson’s one-dose vaccine.
AstraZeneca and J&J are reportedly looking into modifications to address the blood clotting risk.