Effectiveness of Measles Vaccination and Immune Globulin Post-Exposure Prophylaxis in an Outbreak Setting-New York City, 2013.

Background: Measles, mumps, and rubella vaccine (MMR) or immune globulin (IG) are routinely used for measles post-exposure prophylaxis (PEP). However, current literature on the effectiveness of measles PEP is limited and variable. Here, we examined the effectiveness of MMR and IG PEP among children exposed to measles during an outbreak in New York City (NYC) in 2013.

Methods: Contacts were identified by the NYC Department of Health and Mental Hygiene between 13 March 2013 and 30 June 2013. Immunity to measles and receipt of PEP was determined for contacts. PEP effectiveness [(1 - relative risk of developing measles) × 100] was calculated for MMR, IG, and any PEP (MMR or IG) for nonimmune contacts aged <19 years.

Results: A total of 3409 contacts were identified, of which 208 (6.1%), 274 (8.0%), and 318 (9.3%) met the inclusion criteria for analysis of MMR, IG, and any PEP effectiveness, respectively. Of the contacts included, 44 received MMR PEP and 77 received IG PEP. Effectiveness of MMR PEP was 83.4% (95% confidence interval [CI], 34.4%, 95.8%). No contact who received IG PEP developed measles; effectiveness of IG PEP was 100% (approximated 95% CI, 56.2%, 99.8%). Effectiveness of receiving any PEP (MMR or IG) was 92.9% (95% CI, 56.2%, 99.8%).

Conclusions: Contacts who received PEP were less likely to develop disease. Our findings support current recommendations for administration of PEP following exposure to measles. These results highlight the importance of a rapid public health outbreak response to limit measles transmission following case identification.