This winter, for the first time, there were two vaccines available to prevent respiratory syncytial virus, which is especially dangerous for the elderly and infants. Only one of them — Abrysvo, made by Pfizer — was approved for pregnant women and not for young children.
The distinction apparently slipped by some clinicians and pharmacists.
At least 128 pregnant women were mistakenly given the alternative vaccine — Arexvy, by GSK — and at least 25 children under the age of 2 were vaccinated, the Centers for Disease Control and Prevention warned.
Dr Sarah Long, a pediatric infectious disease specialist and consultant to the agency, said she was “blindsided” by the reports. “It’s very unfortunate that this is happening,” he said.
Arexvy has not been tested in pregnant women or children, so information about its effects in these groups is limited. No serious damage from the bugs has yet been confirmed, but the effect was unknown in the majority of reported cases.
Based on the available data, Dr. Long said she was more concerned about young children who received the RSV vaccine than pregnant women who received Arexvy or their babies. Evidence from animal tests “strongly suggests” that Arexvy may make RSV infection worse in children younger than 2 years old, rather than reducing it, according to the Food and Drug Administration.
To prevent this, the CDC recommended that children who missed a vaccine also receive nirsevimab (sold as Beyfortus), a monoclonal antibody that provides strong immune protection, while the RSV season lasts.
Up to 80,000 children under the age of 5 are hospitalized with RSV infections each year in the United States, and the virus is the leading killer of children worldwide.
In 2022, GSK stopped clinical trials of a version of its vaccine in pregnant women after a safety review showed an increased risk of premature birth. The company also found an increase in neonatal deaths, but said it was a consequence of premature births.
GSK is still tracking participants in these trials and sharing the data with the FDA, said Alison Hunt, a company spokeswoman.
In the Pfizer trial, Abrysvo also showed a slightly higher risk of preterm birth up to 37 weeks’ gestation, but the increase was not statistically significant.
However, out of concern about the potential risk of preterm birth, the FDA approved Abrysvo only for pregnant women between 32 and 36 weeks’ gestation. (The goal is to produce antibodies in women that can be passed on to infants, protecting them soon after birth.)
CDC advisors further narrowed the window by recommending shots for pregnant women only from September to January, with the goal of protecting babies born during the RSV peak season.
“In reviewing the data we felt somewhat conservative,” said Dr. Camille Kotton, a physician at Massachusetts General Hospital and one of the agency’s scientific advisors.
“If there was a problem with preterm labor, having it in the last eight weeks of pregnancy would likely have less of an impact than earlier in the pregnancy,” he said.
Some infants who mistakenly received RSV vaccine were intended to receive nirsevimab. The GSK vaccine appears to have been given to some pregnant women because the Pfizer vaccine was not as widely available and pharmacists believed they were interchangeable.
Amy Gardner, 39, a former kindergarten teacher in Cleveland, Tenn., said she tried to locate Pfizer’s RSV vaccine at several pharmacies for her pregnant daughter. In mid-September, on the last day her daughter was eligible to receive the vaccine, she found a pharmacy that said it was stocked, Ms. Gardner said.
But her daughter received Arexby.
“We’re all human, but there have to be more checks and balances than that,” Ms Gardner said. She believes the shooting led to her daughter going into premature labor a few hours later.
The errors were reported to a federal database called the Vaccine Adverse Event Reporting System. Those administering the vaccines may have been confused in part by the similarity of the two names, experts said.
“It’s just horrible – why, why did they do this?” said Dr. Long. “A lot of people were paid a lot of money to come up with these names, and I don’t understand them.”
Dr. Kotton urged the FDA to encourage companies to give similar products clearly distinct names. “When there is going to be a parallel release of vaccines, whenever possible, it would probably be good to have different names,” he said.
Dr. Long said she was concerned about young children receiving RSV vaccines. Because they are not approved for children, pediatricians’ offices, which usually administer vaccines, should not have any in stock.
“It’s important to find out how this happened, because we don’t want it to happen again,” he said.
