Impact on Epidemic Measles of Vaccination Campaigns Triggered by Disease Outbreaks or Serosurveys: A Modeling Study.

Tuesday, 1st of November 2016 Print

PLoS Med. 2016 Oct 11;13(10):e1002144. doi: 10.1371/journal.pmed.1002144. eCollection 2016.

Impact on Epidemic Measles of Vaccination Campaigns Triggered by Disease Outbreaks or Serosurveys: A Modeling Study.

Lessler J1 Metcalf CJ234 Cutts FT5 Grenfell BT24.

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Abstract

BACKGROUND:

Routine vaccination supplemented by planned campaigns occurring at 2-5 y intervals is the core of current measles control and elimination efforts. Yet large unexpected outbreaks still occur even when control measures appear effective. Supplementing these activities with mass vaccination campaigns triggered when low levels of measles immunity are observed in a sample of the population (i.e. serosurveys) or incident measles cases occur may provide a way to limit the size of outbreaks.

METHODS AND FINDINGS:

Measles incidence was simulated using stochastic age-structured epidemic models in settings conducive to high or low measles incidence roughly reflecting demographic contexts and measles vaccination coverage of four heterogeneous countries: Nepal Niger Yemen and Zambia. Uncertainty in underlying vaccination rates was modeled. Scenarios with case- or serosurvey-triggered campaigns reaching 20% of the susceptible population were compared to scenarios without triggered campaigns. The best performing of the tested case-triggered campaigns prevent an average of 28613 (95% CI 25722-31505) cases over 15 y in our highest incidence setting and 599 (95% CI 464-735) cases in the lowest incidence setting. Serosurvey-triggered campaigns can prevent 89173 (95% CI 86768-91577) and 744 (612-876) cases respectively but are triggered yearly in high-incidence settings. Triggered campaigns reduce the highest cumulative incidence seen in simulations by up to 80%. While the scenarios considered in this strategic modeling exercise are reflective of real populations the exact quantitative interpretation of the results is limited by the simplifications in country structure vaccination policy and surveillance system performance. Careful investigation into the cost-effectiveness in different contexts would be essential before moving forward with implementation.

CONCLUSIONS:

Serologically triggered campaigns could help prevent severe epidemics in the face of epidemiological and vaccination uncertainty. Hence small-scale serology may serve as the basis for effective adaptive public health strategies although in high-incidence settings case-triggered approaches are likely more efficient.

 

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