Rotavirus vaccine: fingers crossed

by revere, cross-posted at Effect Measure

Earaches, respiratory infections and diarrhea are the bane of existence for young parents. All are potentially the result of contagious agents. The most common agent for diarrhea in infants and children is rotavirus, a double-stranded DNA virus, that CDC estimates causes 400,000 doctor visits, 200,000 emergency room visits and 55.000 to 70,000 hospitalizations each year in the under 5 year old age group. Infection produces significant immunity, and while there are seven different serotypes (A through G), 90% of infections are serotype A. In addition to diarrhea, rotavirus infections cause nausea, vomiting and fever, often with dehydration that can be fatal to an infant. By the time a child turns five, he or she is likely to have had a rotavirus infection. So this virus causes a lot of sickness and even more dollars. A recent estimate is that each hospitalization costs about $3600.

If rotavirus infection could be prevented by a vaccine it would have a major public health impact. In the 1990s a vaccine to do just that went on the market. It was thought to be safe but soon reports started appearing that it was associated with an increased risk of intestinal obstruction by intussusception, a blockage of the intestinal tract caused by a telescoping of one length of intestinal tract into another. The rotavirus vaccine was taken off the market. In 2006 US FDA approved a new rotavirus vaccine (RotaTeq, marketed by Merck). As with the previous vaccine, clinical trials appeared to show the new vaccine was safe, but those trials are much smaller than the population that eventually winds up getting a vaccine, so relatively rare events like intussusception aren't picked up. Therefore intensive surveillance for adverse events and particularly for intussusception, was put in place. So far the rate of intussusception after vaccination with the new vaccine is no more than what would be expected if the vaccine were not given, perhaps lower. The surveillance covered a 19 month period after vaccine release during which 9 million doses were distributed. Thus all the evidence suggests the vaccine is indeed safe, but does it work?

This week the Infectious Disease Society of America (IDSA) is holding its 48th Annual Meeting in Washington, DC, and among the papers are reports from CDC and Merck on how well RotaTeq is working (hat tip reader stillwagon):

A vaccine against rotavirus, the leading cause of diarrhea in infants, has led to a dramatic drop in hospitalization and emergency room visits since it came on the market two years ago, doctors reported Saturday.A bonus: the vaccine seems to be preventing illness even in unvaccinated children by cutting the number of infections in the community that kids can pick up and spread.

"We're a little surprised by the degree of impact given the coverage we've achieved," said Jane Seward of the federal Centers for Disease Control and Prevention. Only about half of young children had received the vaccine and very few had received all three doses when the studies were done.

[snip]

Since Merck & Co.'s Rotateq came out in 2006, hospital visits and stays due to the virus have dropped 80 percent to 100 percent, studies by the CDC and several other groups show.

Last winter, rotavirus cases started and peaked two to three months later and were much less extensive than in previous years, CDC scientists report. Hospitals in a network that tracks these cases for the CDC saw more than an 80 percent drop in admissions from them, one study showed.

Another study, by Merck, found a 100 percent drop in hospitalizations and ER visits during the 2007 and 2008 rotavirus seasons compared to previous ones. The study was based on a review of health insurance claims for about 61,000 infants and diagnoses by doctors in routine clinical practice.

Rotateq is an oral vaccine given at two, four and six months of age. In June, a second rotavirus vaccine came on the market -- GlaxoSmithKline's Rotarix. It requires only two doses, completed by four months of age. (Marilynn Marchione, AP)

 

I know there is a lot of suspicion and skepticism about vaccines today. But if true this is pretty good news. We are talking about a virus that kills 1600 babies a day, worldwide. It is a major cause of infant mortality in the developing world. The data suggest a significant "herd immunity" effect (whereby unvaccinated children are also protected by the reduced transmission rate of those immune). This means there is a multiplier effect from using the vaccine.

So we'll see. I'm keeping my fingers crossed, not because I think it will do any good, but because, as Nils Bohr said about the lucky horseshoe over his lab bench, I understand it works even if you don't believe in it.