Link strengthened between routine rotavirus vaccination and indirect benefits

The 2007-2008 rotavirus season was milder than those observed in previous years, with delayed onset, shorter duration and fewer cases reported since the implementation of routine rotavirus vaccination, according to results from the CDC’s National Respiratory and Enteric Virus Surveillance System.

“These changes coincide with increasing vaccine coverage, but the scope of the changes seems greater than that expected on the basis of direct protective effects of vaccination, suggesting possible indirect benefits to unvaccinated individuals,” the researchers wrote. They attributed these benefits to possible “herd effects.”

The researchers analyzed rotavirus trends reported from 33 labs that were part of the NREVSS sentinel network from July 2000 to June 2008. Compared with rotavirus seasons prior to 2006, the following changes occurred after routine vaccination:

Season onset after routine vaccination was delayed 15 weeks — occurring in late February rather than mid-December.

The most recent season lasted 14 weeks compared with a median duration of 26 weeks in the prevaccination era.

lThe 2007-2008 season peaked eight weeks later than usual, with the median national peak occurring in late April compared with early March.

lA greater than 50% decline in the proportion of positive test results in 2007-2008 was reported in 79% of the labs compared with the median from 2000 to 2006 and a greater than 75% reduction in 39% of the labs.

Although nationally representative data on rotavirus vaccine coverage for 2007-2008 are unavailable at this time, information from six sentinel site systems indicated that the median coverage for one dose of rotavirus vaccine among infants aged 3 months has increased to 58% since June 2006 (range: 51%-68%).

“Young infants are likely to experience the most severe disease, with higher rates of viral shedding during their first rotavirus infection, and achieving even moderate levels of vaccine coverage in this age group could substantially affect overall transmission patterns of rotavirus,” the researchers wrote.

These findings echo previous reports of the substantial benefits associated with routine rotavirus vaccination.

Tate JE. Pediatrics. 2009;doi:10.1542/peds.2008-3528.