1386. Effectiveness of Measles-Containing Vaccine during a Measles Outbreak, Pohnpei, Federated States of Micronesia - 2014
Session: Oral Abstract Session: Pediatric Vaccines: Measles and Pertussis
Saturday, October 10, 2015: 11:00 AM
Room: 32--ABC
Background: In June 2014, the state of Pohnpei in the Federated States of Micronesia reported the first measles outbreak in 20 years.  Pohnpei had 1-dose measles-containing vaccine (MCV) coverage of 85% and 2-dose coverage of 72% among 2 year olds in 2013.  Of outbreak cases, 71% had previously received ≥1 dose of MCV.  A mass vaccination campaign targeted persons aged 6 months to 49 years.  We assessed vaccine effectiveness (VE) of MCV using a secondary attack rate (SAR) study.

Methods: A measles case was defined according to the Council of State and Territorial Epidemiologists guidelines.  Data on exposure and symptoms were collected for household (HH) contacts of the primary case (the first measles case in the HH); immunization records provided vaccination status. Secondary cases were HH contacts with rash onset 7-21 days after rash onset in the primary case.  SAR was defined as the proportion of secondary cases among HH contacts.

Results: 318 contacts from 80 HH were included; median age was 14 years and 157 (49%) were female.  VE of pre-outbreak doses was 33% (95% CI -93, 77) for 1 dose, 62% (95% CI 2, 85) for 2 doses and 100% (95% CI 94, 100) for 3 doses.  VE of pre-outbreak doses received in 2010 or later was 87% (95% CI 51, 97), but VE for doses received before 2010 ranged from 40-59% (p>0.05).  VE of campaign doses received > 4 days before primary case rash onset was 92% (95% CI 70, 98).  VE was 79% (95% CI 18, 94) for doses received 1-4 days before primary case rash onset, 77% (95% CI 27, 93) for doses received on the day of primary case rash onset until 3 days afterwards, and 55% (95% CI -27, 84) for doses received 4-21 days after primary case rash onset.

Conclusion: Vaccine failure was a major source of measles susceptibility in this outbreak as evidenced by the low overall VE of MCV, especially among 2-dose recipients.  Potential reasons for lower VE among persons vaccinated before 2010 include historical cold chain inadequacies or waning of immunity.  High VE for recent vaccinations is reassuring. VE of doses given > 4 days before primary case rash onset supports rapid implementation of vaccination campaigns in outbreak settings. The high VE of doses given 4 days before to 3 days after primary case rash onset highlights the benefit of identifying and vaccinating susceptible contacts in the post-exposure prophylaxis period.

Craig Hales, MD1, Mark Papania, MD1, Maribeth Larzelere, MPH2, Sameer Gopalani, MPH3, Emmaculate Lebo, MD4, Gregory S. Wallace, MD, MPH, MS1, Edna Moturi, MD4, Paul Rota, PhD1 and Mona Marin, MD1, (1)Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, GA, (2)Immunization Services Division, Centers for Disease Control and Prevention, Atlanta, GA, (3)Department of Health and Social Affairs, Palikir, Micronesia, (4)Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, GA

Disclosures:

C. Hales, None

M. Papania, None

M. Larzelere, None

S. Gopalani, None

E. Lebo, None

G. S. Wallace, None

E. Moturi, None

P. Rota, None

M. Marin, None

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