ATLANTA (FRONTLINE MEDICAL NEWS)Norovirus vaccines currently in development should be administered before age 6 months to provide the most benefit, according to the findings of a global age distribution study.

The meta-analysis of data from 35 papers representing children from 23 countries showed that completion of the vaccination schedule by age 6 months could prevent about 85% of pediatric cases, compared with only about 50% of cases with delivery by age 12 months, Kayoko Shioda, D.V.M., of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention, Atlanta, reported in a poster at the International Conference on Emerging Infectious Diseases.

For the study, Dr. Shioda and her colleagues at the CDC looked at studies involving norovirus cases among children under age 5 years. After weighting by the number of pediatric cases in each study, they found that 13% of cases occurred in those aged 0-5 months, 33% occurred among those aged 6-11 months, 36% occurred in those aged 12-23 months, and 18% were in those aged 24-59 months.

The age distribution was younger in developing countries vs. developed countries, in low income vs. high income countries, and in inpatient vs. outpatient and community settings, she said in an interview.

Also, the age distribution of severe cases was younger than for mild cases, she noted.

The findings suggest that early vaccination is particularly important in low-income settings, which had a younger age distribution that might be attributable to poorer hygiene and sanitation and/or higher levels of contact between individuals, she said, noting that the cumulative proportion of cases by 12 months was reduced by 4.1% for every $10,000 increase in per capita gross domestic product after controlling for study settings.

“We have to vaccinate as early as possible in low income countries. Our recommendation is to do vaccination by 1 month,” she added.

The findings were published earlier this summer (Vaccine. 2015, June doi: 10.1016/j.vaccine.2015.05.051 ).

Norovirus is increasingly recognized as a main cause of acute gastroenteritis, which occurs most often in young children. No vaccine is currently available, but one developed by Takeda is currently entering phase III trials, Dr. Shioda said.

This study was supported by the Oak Ridge (Tenn.) Institute for Science and Technology. Dr. Shioda reported having no other relevant disclosures.