The current generation of vaccines against rotavirus, the leading cause of diarrheal disease in children under five years old, was introduced just a decade ago. In the intervening years, 81 countries have implemented rotavirus vaccination to prevent diarrheal disease. Earlier this month, 350 experts from 50 countries met in Melbourne, Australia, for the 12th International Rotavirus Symposium to share recent data and assess the state of global rotavirus prevention 10 years later.

Gagandeep Kang gave this year’s Roger Glass Lecture, titled, “Can we do better? Oral vaccines in the developing world.” The lecture contained a comprehensive overview of the current performance of oral vaccines in low- and middle-income countries and identified critical factors affecting oral vaccine performance. Dr. Kang stressed the need to understand how the environment surrounding the vaccine – from a child’s nutritional state to the natural composition of bacteria living in the digestive system – affects vaccine performance.

The symposium’s host city was particularly appropriate this year, as Melbourne is home to Professor Ruth Bishop, a driving force behind the decades-long search for a safe, effective vaccine against rotavirus. Bishop led the team at The Royal Children’s Hospital Melbourne that discovered the virus in 1973 and was the first to demonstrate the development of protective immunity following natural rotavirus infection in infants. For her vast contribution to the field of rotavirus prevention, Bishop was honored at this year’s symposium with a roundtable discussion on women leaders in the scientific advancement of rotavirus.

A primary focus of the symposium was to share recent data on the long-term impacts of rotavirus vaccination, with the goal of informing future policymaking decisions on rotavirus prevention. Representatives from public health agencies and universities around the world, including the World Health Organization’s Global Rotavirus Surveillance Network and U.S. Centers for Disease Control and Prevention, presented findings from surveillance programs that were established to monitor the global burden of rotavirus infection and measure vaccine impact.

As reported in a session devoted to the post-licensure impact of rotavirus vaccination, considerable progress has been made in expanding rotavirus vaccine coverage, which in some countries has reached 85 to 95 percent. However, rotavirus vaccination rates remain low in many other countries, possibly due to perceived low burden of disease in certain areas, insufficient infrastructure to keep the temperature-sensitive vaccines refrigerated, or fear due to risk of possible intussusception – a rare but serious side effect that caused the first-generation rotavirus vaccine to be pulled from the market.

Rotavirus vaccines have proven to be effective at preventing hospitalizations due to diarrheal disease and have the greatest impact on children and infants. Some sites reported a drop in diarrheal disease even in unvaccinated segments of the population, likely due to indirect herd protection through reduced transmission of rotavirus. Despite these successes, a cause for concern highlighted at the symposium is the pronouncedly lower effectiveness of the vaccine when implemented in low- to middle-income countries relative to high-income countries. While it is still unclear why that gap in effectiveness exists, several avenues of research have presented intriguing possibilities.

One potential explanation may lie in the findings of a vaccine effectiveness study performed in Botswana, where the vaccine was reported to be significantly less effective in preventing disease in moderately to severely undernourished children relative to their well-fed counterparts, indicating diet may play a role in how well the vaccine works. Another hypothesis explores the possibility that non-disease-causing bacteria naturally residing in the intestines, which can change based on environmental factors like nutrition and hygiene, may shape how an infant’s body forms an immune response after vaccination.

After a decade of immunization against rotavirus, an estimated 2.4 million deaths will have been averted between 2007 and 2025. This year’s symposium served as an excellent opportunity for experts and stakeholders in the field to come together to plan future efforts to ensure such progress continues.

The 12th International Rotavirus Symposium was convened by the Sabin Vaccine Institute in collaboration with the Bill and Melinda Gates Foundation, the U.S. Centers for Disease Control and Prevention, the U.S. National Institutes of Health Fogarty International Center, Murdoch Childrens Research Institute, the University of Melbourne, PATH and the ROTA Council.