The high prevalence of norovirus infection among children in countries with increased diarrheal disease burden highlights a need for vaccine development, according to recent research in Clinical Infectious Diseases.
“Norovirus is a common cause of childhood diarrhea which remains the second-leading cause of under 5 morbidity and mortality globally,” Saba Rouhani, DrPH, MSc, of Johns Hopkins School of Public Health, and colleagues wrote. “This study highlights the significant burden of norovirus at eight sites in variable epidemiologic settings using a unified protocol and sensitive diagnostic methods.”
The researchers studied a birth cohort of 1,457 children from Bangladesh, Brazil, Pakistan, Peru, South Africa, Tanzania, Nepal and India where high rates of malnutrition and diarrheal disease occur. Participants were enrolled by age 17 days and followed until age 24 months from November 2009 to February 2012. During the study period, 7,077 diarrheal stools were collected for testing. The researchers classified a subset of 199 children, who also provided comparison asymptomatic samples, to evaluate incidence rates and acquired immunity.
Study data indicated that 89% of participants experienced at least one norovirus infection before 24 months. Furthermore, 22.7% of all diarrheal samples tested positive for norovirus pathogens. The researchers said norovirus severity was comparable to other enteropathogens, excluding rotavirus.
Genogroup II infections (n = 346) were more prevalent than genogroup I infections (n = 157), among the study population. Acquired immunity was observed only in children with prior genogroup II infections, with a 27% reduction in risk for future norovirus infection (P = .01).
“We estimate that an effective vaccine could avert approximately 99 million episodes of diarrhea among children aged 6 to 24 months,” Rouhani and colleagues wrote. “This work demonstrates the clear burden of norovirus in early childhood, particularly genogroup II, and evidence for natural immunity, thus providing strong impetus for ongoing vaccine development.”
In a related editorial, Benjamin A. Lopman, PhD, MSc, of the CDC’s Division of Viral Diseases, and Nicholas C. Grassly, DPhil, of the department of infectious disease epidemiology at the Imperial College London, highlighted some of the limitations of Rouhani and colleagues’ study, while emphasizing the importance of their large-scale norovirus research.
“The identification of potentially modifiable host factors such as acquired immunity and undernutrition that can mediate risk of infection and disease outcomes are important advances,” Lopman and Grassly wrote. “However, these factors do not fully explain which children get infected and how severe their disease is. Interactions with other pathogens, commensals, and host genetic factors likely play a role. Although the picture of norovirus is starting to become clearer, there are many details still to fill in.” – by David Costill
Disclosure: The researchers report no relevant financial disclosures.