To address these uncertainties, the IVI in collaboration with NICED conducted a phase 4 cluster-randomized effectiveness trial, which randomized 80 geographic clusters of an urban Kolkata slum to either Vi or a control vaccine. Over two years of follow-up, the Vi group was shown to have 61 percent fewer episodes of typhoid than the control group. Protection of vaccinated children under five years of age by Vi was even higher, 80%. Interestingly, unvaccinated neighbors of Vi vaccinated persons had a 44 percent lower risk of typhoid, indicating that Vi vaccine conferred substantial herd protection. The overall level of protection among all residents of the Vi clusters, regardless of whether they were vaccinated was 57 percent. Since the coverage of residents of the Vi clusters was about 60%, this observation indicates that Vi vaccine prevented as many cases of typhoid in the total population as a vaccine that was nearly 100% protective in vaccinated persons.
"The protection for children under the age of five years is important because this age group has been shown to be at high risk for typhoid fever in many areas where the disease is endemic," said Dr. John Clemens, Director-General of the IVI and an international expert in vaccine evaluation. In a separate IVI study conducted in five Asian countries and supported by the Bill and Melinda Gates Foundation, children less than five years of age were found to have high rates of typhoid in Kolkata, India, Jakarta, Indonesia and Karachi, Pakistan, confirming that the disease is not limited to school-aged children and adults.
The IVI-NICED study, which was supported by the Gates Foundation and the governments of Korea, Sweden, and Kuwait, also revealed that delivering the low-cost Vi typhoid vaccine is l
|Contact: Tae Kyung Byun|
International Vaccine Institute