Learning Objectives for this Presentation:
By the end of the presentation, participants will be able to understand the impact of different rotavirus vaccination strategies.

Background:
The first rotavirus vaccine licensed in the United States, Rotashield, was associated with a serious but rare adverse event—intussusception (IS). New rotavirus vaccines will soon be licensed, and IS incidence rates suggest that natural cases of IS will occur by chance following immunization, likely raising concerns about whether such cases were “caused” by vaccine.

Objectives:
To model and compare the number of IS cases expected by chance alone under two rotavirus vaccination strategies.

Methods:
We used national DTP vaccine coverage rates and IS incidence by age (months) to model the number of IS cases that would occur by chance alone within two weeks post-vaccination for two immunization strategies: (1) a Strict Schedule limiting immunization to within one month of the designated age for each dose, versus (2) a Free Schedule allowing infants to be immunized against rotavirus at any time up to one year of age.

Results:
The number of IS cases during the two-week post-vaccination window was 24% lower for the Strict versus the Free Schedule (138 vs. 182). This reduction was due to the lower number of infants fully immunized with the Strict Schedule (vaccine coverage for three doses, 67% vs. 89%). Risk of IS occurring by chance in the two-week post-vaccination window was the same between schedules (2.27 vs. 2.26/100,000 doses). Most cases occurred following the second or third dose.

Conclusions:
A rotavirus vaccination schedule with fewer age restrictions did not differ in risk of IS due to chance alone in the two-week post-vaccination window compared to an age-restricted strategy. National rotavirus immunization policy should be prepared to address concerns about naturally occurring IS due to chance alone following vaccination.