Rotavirus Vaccine Withdrawal

Rotavirus Vaccine Withdrawal
(Biotechnology Newswatch, November 1, 1999)

Wyeth-Lederle Vaccines, a division of American Home Products Corporation, has voluntarily withdrawn its RotaShield from the market following reports of increased rates of intussusception in infants who were immunized with the rotavirus vaccine.

The Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention has also withdrawn its recommendation for all infants to receive the vaccine at two, four, and six months of age.

Intussusception, a type of bowel obstruction in which the bowel folds on itself, had been reported in pre-licensure studies of RotaShield and was mentioned in its package insert, but the incidence was not higher than the usual background rate.

However, once the vaccine was licensed and given to about 900,000 infants, more cases of intussusception were reported to the Vaccine Adverse Reporting System (VAERS), a passive surveillance system run by the CDC and the Food and Drug Administration. The vaccine was temporarily halted July 13th, pending the results of ongoing studies.

By October 15th, the VAERS had received 102 reports of intussusception in infants who had received RotaShield. Of those, 57 occurred within 7 days after receipt of the vaccine about four times more than the expected number.

Twenty-nine of the infants required surgery and one died. Further analyses showed that the risk of intussusception was clearly elevated within three to seven days after the first vaccine dose, and still slightly higher than expected at eight to 14 days. There appeared to be no further risk after two weeks.

Studies are now underway to determine how the live, oral, tetravalent rhesus-human reassortment rotavirus vaccine could cause intussusception. This is important because other rotavirus vaccines are currently in development. Most of these are bovine, rather than rhesus-based.

Researchers are puzzled as to why an attenuated virus would be more likely to cause intussusception than would natural rotavirus. Yet that seems to be the case, since the incidence of intussusception does not typically peak in the winter months as rotavirus diarrhea does.

Rotavirus is the most common cause of severe diarrhea in infants and children. It is responsible for 500,000 physician visits, 50,000 hospitalizations, and about 20 infant deaths each year in the United States, and up to one million deaths annually worldwide. Unlike other gastric pathogens, rotavirus isn't reduced by cleaning up the water supply.

A World Health Organization official told the ACIP, "The developing world needs a rotavirus vaccine." ###