The Centers for Disease Control and Prevention (CDC) has now identified 28 cases of blood clots with low platelets in people who received the Johnson & Johnson coronavirus vaccine, agency officials said Wednesday.
The 28 cases were found after more than 8.7 million doses of the single injection vaccine were administered, the agency said. There were no confirmed cases involving any of the mRNA vaccines from Pfizer-BioNTech or Moderna.
According to the agency, four of the 28 people with the condition remained in the hospital as of May 7, one of whom was in the ICU, and two have been discharged to a post-acute care facility.
Health agencies paused use of the vaccine for 10 days last month to investigate the rare and potentially fatal side effect, and to educate providers on how to treat it. Twelve of the patients were treated with heparin, which is a blood thinner normally used for blood clots, but has been shown to make this specific condition worse.
At the time vaccinations were cleared to resume on April 23, the CDC had identified 15 cases out of slightly less than 8 million shots administered.
The agency on Wednesday said all 28 confirmed cases occurred before the pause began on April 13. The median age of patients was 40 and their ages ranged from 18 to 59. Of the 28 cases, 22 occurred in women and six occurred in men.
The CDC said the symptoms of the condition, known as thrombosis with thrombocytopenia syndrome, appear similar to what is being observed following AstraZeneca COVID-19 vaccinations in Europe.
Women who were between the ages of 30 and 39 accounted for the biggest risk group, but the largest increase in cases occurred in women between the ages of 40 and 49.
The CDC said the known potential benefits of the vaccine continued to outweigh its potential risks.