Measles Outbreak Associated With Low Vaccine Effectiveness Among Adults in Pohnpei State Federated States of Micronesia 2014.

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Open Forum Infect Dis. 2016 Mar 24;3(2):ofw064. doi: 10.1093/ofid/ofw064. eCollection 2016.

Measles Outbreak Associated With Low Vaccine Effectiveness Among Adults in Pohnpei State Federated States of Micronesia 2014.

Hales CM¹ Johnson E² Helgenberger L³ Papania MJ¹ Larzelere M¹ Gopalani SV³ Lebo E⁴ Wallace G¹ Moturi E⁴ Hickman CJ¹ Rota PA¹ Alexander HS² Marin M¹.

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Abstract

Background.  A measles outbreak in Pohnpei State Federated States of Micronesia in 2014 affected many persons who had received ≥1 dose of measles-containing vaccine (MCV). A mass vaccination campaign targeted persons aged 6 months to 49 years regardless of prior vaccination. Methods.  We evaluated vaccine effectiveness (VE) of MCV by comparing secondary attack rates among vaccinated and unvaccinated contacts after household exposure to measles. Results.  Among 318 contacts VE for pre campaign MCV was 23.1% (95% confidence interval [CI] -425 to 87.3) for 1 dose 63.4% (95% CI -103 to 90.6) for 2 doses and 95.9% (95% CI 45.0 to 100) for 3 doses. Vaccine effectiveness was 78.7% (95% CI 10.1 to 97.7) for campaign doses received ≥5 days before rash onset in the primary case and 50.4% (95% CI -52.1 to 87.9) for doses received 4 days before to 3 days after rash onset in the primary case. Vaccine effectiveness for most recent doses received before 2010 ranged from 51% to 57% but it increased to 84% for second doses received in 2010 or later. Conclusions.  Low VE was a major source of measles susceptibility in this outbreak; potential reasons include historical cold chain inadequacies or waning of immunity. Vaccine effectiveness of campaign doses supports rapid implementation of vaccination campaigns in outbreak settings.