Newborn screen can protect infants from vaccine-acquired rotavirus

A vaccine designed to protect infants against rotavirus, the leading cause of childhood diarrhoea, can actually cause the disease in infants born with severe combined immunodeficiency, said experts at Baylor College of Medicine in a study that appears in the current edition of the New England Journal of Medicine.

The vaccine provides substantial benefit against rotaviral infection. Worldwide, it has prevented potentially deadly infections in millions of children. However, infants who are born lacking a protective immune system because of their genetic disorder can actually acquire the viral infection from the vaccine, the researchers said. The vaccine, given in three doses between 6 and 32 weeks of age, is live, but it has been weakened so that it does not present a threat of infection to children with normal immunity.

In this report, experts examined three cases in which infants developed rotavirus disease after receiving the live attenuated rotavirus vaccine. "All three infants (in the study) were vaccinated before they were diagnosed with severe combined immunodeficiency," said Dr Paula Hertel, assistant professor of pediatrics-gastroenterology at BCM and Texas Children’s Hospital, co-author of the study. "If the children could have been caught in a screening test done within days of birth, they may not have received the vaccine."

Expanded testing

While current routine newborn screening does test for many diseases, severe combined immune deficiency is not one of them.

Usually, experts recommend that children with severe combined immune deficiency not receive live vaccines. However, this vaccine must be given before most children are diagnosed with the immune disorder. The Advisory Committee on Heritable Disorders in Newborns and Children recently recommended that severe combined immunodeficiency be included as a part of the newborn screen.

"The disease in these infants was confined to the gastrointestinal tract, but in other cases there is potential that it could disseminate to other organs besides the intestines," said Dr Stuart Abramson, associate professor of paediatrics in the section of allergy and immunology at BCM and Texas Children’s Hospital and senior author of the study.

No immune system protection

Children with severe combined immunodeficiency lack protection provided by key components of the immune system – the T- and B-cells. As a result, these children have no protection against many infections that can become life-threatening. Fortunately, the disorder is rare, affecting between 1 in 50,000 to 100,000 live births.

Scientists analysed the viral genetic material in stool specimens from the three children. This enabled them to determine that the rotavirus was of vaccine origin. This study led to a change in the vaccine exclusions listed on the vaccine manufacturer’s label to include a history of severe combined immunodeficiency.

The children did not successfully fight the infection until they underwent bone marrow transplantation or enzyme replacement therapy that gave them a functioning immune system, said Abramson.

The vaccine is very important for healthy infants, and in the United States, rotavirus cases decreased by 50 percent after the first season of vaccinations against the illness, said Hertel.

(Source: Baylor College of Medicine: New England Journal of Medicine: February 2010)