Recent estimates from the Global Burden of Disease Study 20151
indicate that although deaths from diarrhea have decreased by 20.8% during the past 5 years, it remains one of the world’s leading killers of children younger than 5 years, causing around 500,000 deaths each year. In this context, rotavirus was found to be the leading cause of diarrhea-associated mortality, accounting for approximately 200,000 deaths annually, most of which (~90%) occurred in low- and middle-income countries of sub-Saharan Africa and southern Asia.2,3
The first licensed rotavirus vaccine (Rotashield, Wyeth-Lederle Vaccines) was withdrawn from the US market in 1999, less than 1 year after its licensure, because of its association with an increased risk of intussusception, estimated at 1 excess case (an additional case that would not have occurred naturally, for example, in the absence of rotavirus vaccination) per 10,000 vaccinated infants. This is a rare severe medical condition in which a segment of the intestine invaginates into the adjoining intestinal lumen, causing a bowel blockage.4
Almost 7 years after the withdrawal of Rotashield, 2 new-generation, oral, live-attenuated rotavirus vaccines became available. These were a 2-dose, monovalent human vaccine (Rotarix, GlaxoSmithKline Biologicals) and a 3-dose, pentavalent bovine-human reassortant vaccine (RotaTeq, Merck & Co.). Before licensure, both had undergone extensive clinical and safety studies involving 101,671 and 84,592 infants, respectively. In these trials, large sample sizes were necessary to rule out any risk of intussusception at a magnitude similar to that of Rotashield.2
Both vaccines proved highly efficacious (>80% protective efficacy) against severe rotavirus gastroenteritis in the United States, Europe, and Latin America.2
As expected, a trend for lower efficacy was seen in resource-limited countries of sub-Saharan Africa and southern Asia, even though the overall impact of vaccination was significant, owing to the high rates of severe rotavirus diarrheal cases in these settings. Importantly, these trials’ results have not revealed any increased risk of intussusception following administration of vaccine doses.
In 2006, the World Health Organization (WHO) reviewed available data from pre-licensure studies in Europe and the Americas and recommended rota-virus vaccine introductions into the national immunization programs (NIPs) of those regions. In 2009, with the availability of additional efficacy data from trials in Africa and Asia, WHO recommended routine rotavirus vaccination for all countries. As of March 2007, 92 (47%) of the targeted 194 countries around the world had introduced rotavirus vaccines into their NIPs, including universal (n = 85) and sub-national (n = 7) introductions.5,6