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Triggered vaccination campaigns could reduce size, severity of measles outbreaks
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Supplemental vaccination campaigns triggered by measles outbreaks could significantly reduce incidence and prevent more severe outbreaks, with potential to be practiced as an epidemic control activity, according to a recent modeling study.
“The 2009 WHO guidelines for outbreak response in mortality reduction settings and the WHO Global Measles and Rubella Strategic Plan for 2012 to 2014 extended the ‘static’ control strategies to include the possibility of reactive responses,” Justin Lessler, PhD, MHS, an associate professor in the department of epidemiology at Johns Hopkins Bloomberg School of Public Health, and colleagues wrote. “Outbreak response vaccination was recommended for outbreaks occurring in measles mortality reduction areas, based on evidence that epidemics build sufficiently slowly that large numbers of cases can be averted given a sufficiently prompt reaction.”
To evaluate the efficacy of supplemental vaccination campaigns triggered by disease outbreaks, Lessler and colleagues simulated measles incidence using stochastic age-structured epidemic models based on four different occurrence levels in Nepal, Niger, Yemen and Zambia. The researchers compared case- or serological survey-triggered vaccination campaign scenarios that affected 20% of the susceptible populations with scenarios without triggered campaigns. All simulations included regularly planned supplemental immunization activities to ensue every 5 years with 80% coverage of the target population of children aged 9 to 59 months.
Model results showed that campaigns triggered by outbreaks could prevent an estimated 28,613 (95% CI, 25,722-31,505) cases spanning 15 years in the researchers’ highest incidence setting and 599 (95% CI, 464-735) cases in the lowest incidence setting. By contrast, triggered campaigns reduced the highest cumulative incidence in simulations by 80% at best, and serological survey prompted campaigns prevented 89,173 (95% CI, 86,768-91,577) cases at highest incidence and 744 (95% CI, 612-876) cases at lowest incidence in the simulations; however, they would need to occur annually to yield these outcomes.
“We found that this positive impact is observed even for campaigns reaching 20% or less of the unimmunized population, and the largest impact is observed for serologically triggered surveys,” the researchers wrote. “Overall, however, the magnitude of the impact triggered campaigns is highly dependent on the demographic and vaccine coverage context considered.
“Some triggered campaigns strategies may be triggered so often that they become inefficient.” – by Kate Sherrer
Disclosure: This study was supported by a grant from the Science and Technology Directorate, Department of Homeland Security, the Bill and Melinda Gates Foundation (Award #705580-3) and the RAPIDD program of the Science & Technology Directorate, Department of Homeland Security and the NIH Fogarty International Center. The researchers report no relevant financial disclosures.
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