Vaccine efficacy – Rotavirus vaccine RotaTeq (RV5)
A new analysis, published online by The Journal of Infectious Diseases, takes a look at acute gastroenteritis hospitalization (AGE) rates among US children under 5 years old, before and after the introduction of the first Rotavirus vaccine, RotaTeq (RV5) in early 2006. The objective of this analysis was to see if there was any change in gastroenteritis hospitalization rates after the vaccine was licensed for use among infants in the United States. The study I am referring to is this one:
Aaron T. Curns, Claudia A. Steiner, Marguerite Barrett, Katherine Hunter, Emily Wilson, and Umesh D. Parashar
The Journal of Infectious Diseases 2010;201:1617–1624 © 2010 by the Infectious Diseases Society of America. All rights reserved.
Why did they look at gastroenteritis hospitalization rates? Because that disease, commonly referred to as the “stomach flu“, is a viral infection, and rotavirus is the leading cause of severe gastroenteritis in children, credited with causing about 50% of acute gastroenteritis hospitalizations during January-June amoung U.S. children. Logically, if rotavirus causes it, and if an effective vaccine is introduced, we ought to observe statistically significant decreases in gastroenteritis hospitalization rates, and this is what this analysis was set up to do.
Study Summary -The authors gathered approximately 100% complete AGE hospitalization rates for children under 5 years of age, from 18 states, accounting for 49% of the U.S. under 5 children population. Median AGE hospitalization rates from the pre-vaccine years of 2000-2006 were compared with median AGE hospitalization rates from 2007, the first year after the vaccine, and 2008.
Results – Overall AGE hospitalization rates went down by 16% in 2007 and decreased by 45% in 2008. By age group, the reductions line up like this:
- 0-2 months – 28%
- 3-5 months – 42%
- 6-23 months – 50%
- 24-59 months – 45%
Prior to RV5 introduction, children in the 6-11 month age group had the highest hospitalization rates; after vaccine introduction children in the 0-2 month age group had the highest hospitalization rates, and showed the lowest decreases. Given that the first dose of the vaccine is given at 2 months of age, this result is to be expected.
All states experienced reduced rates of hospitalization with the exception of two: Arizona and Nevada which experienced increases of 17.1% and 12.9% respectively, prompting the study authors to note that :
It is noteworthy that 2 participating states, Arizona and Nevada, had 2008 rotavirus seasons that were similar to those in prior seasons. As data become available, it will be of interest to evaluate whether these 2 states had different patterns of RV5 coverage that could explain their distinct 2008 rotavirus seasons.
How should we interpret this analysis? Well, as alwasy the rule of thumb is that one study never proves anything. However, this study does provide strong evidence for a correlation between the RV5 vaccine and lower AGE hospitalization rates. We have to be careful though to remember that correlation does not necessarily imply causation. Given that the post-vaccine data is only for two years, the conclusion that the introduction of the rotavirus vaccine lowered AGE hospitalization rates seems unwarranted at this point. It will be interesting to see if these results hold up 2, 5, 10 years down the road.
Nevertheless, the fact that rotavirus is responsible for 50% of AGE hospitalizations, and the fact that the reductions were more pronounced in the age groups that received vaccines, as compared to the 0-2 month olds who do not, suggests a correlation to some degree. Furthermore, while there is year-to-year variability in AGE hospitalization rates, the 2008 reduction “well exceeded the range of this variability” further suggesting an effect other than regular variability. Lastly, the “consistency of the decrease in acute gastroenteritis hospitalization rates across most states and specifically during the rotavirus season strongly support that these changes resulted from the RV5 vaccination, but the lack of timely national data on RV5 coverage precluded correlation of the decreases with vaccine uptake.” (emphasis added)
Conclusion – This analysis provides good evidence for an association between the introduction of the RV5 vaccine and a considerable reduction in AGE hospitalization rates, especially for 2008. It also provides strong evidence that there may be a correlation between the two, however the lack of nationals RV5 coverage data, and the fact that the post vaccine years provide only 2 data points, preclude us from concluding that the decreases are due to the vaccine. Only further confirmatory studies down the road can provide that additional support that would be needed to conclusively say that the rotavirus vaccine has had a direct effect in reducing AGE hospitalization rates. Until then, we must stick with the strong suggestion that it does.