Consequences of Undervaccination - Measles Outbreak, New York City, 2018-2019.

BACKGROUND: Measles was declared eliminated in the United States in 2000, but the risk of outbreaks owing to international importations remains. An outbreak of measles in New York City began when one unvaccinated child returned home from Israel with measles; onset of rash occurred on September 30, 2018, 9 days after the child returned home. METHODS: We investigated suspected cases of measles by conducting interviews, reviewing medical and immunization records, identifying exposed persons, and performing diagnostic testing. Measles-mumps-rubella (MMR) vaccine (given as either MMR or measles-mumps-rubella-varicella vaccine and collectively referred to as MMR vaccine) uptake was monitored with the use of the Citywide Immunization Registry. The total direct cost to the New York City Department of Health and Mental Hygiene was calculated. RESULTS: A total of 649 cases of measles were confirmed, with onsets of rash occurring between September 30, 2018, and July 15, 2019. A majority of the patients (93.4%) were part of the Orthodox Jewish community, and 473 of the patients (72.9%) resided in the Williamsburg area of Brooklyn, New York. The median age was 3 years; 81.2% of the patients were 18 years of age or younger, and 85.8% of the patients with a known vaccination history were unvaccinated. Serious complications included pneumonia (in 37 patients [5.7%]) and hospitalization (in 49 patients [7.6%]); among the patients who were hospitalized, 20 (40.8%) were admitted to an intensive care unit. As a result of efforts to promote vaccination, the percentage of children in Williamsburg who received at least one dose of MMR vaccine increased from 79.5% to 91.1% among children 12 to 59 months of age. As of September 9, 2019, a total of 559 staff members at the Department of Health and Mental Hygiene (7% of the agency) had been involved in the measles response. The cost of the Department of Health and Mental Hygiene response was $8.4 million. CONCLUSIONS: Importation of measles and vaccination delays among young children led to an outbreak of measles in New York City. The outbreak response was resource intensive and caused serious illness, particularly among unvaccinated children.

Generalisability of vaccine effectiveness estimates: an analysis of cases included in a postlicensure evaluation of 13-valent pneumococcal conjugate vaccine in the USA.

OBJECTIVES: External validity, or generalisability, is the measure of how well results from a study pertain to individuals in the target population. We assessed generalisability, with respect to socioeconomic status, of estimates from a matched case-control study of 13-valent pneumococcal conjugate vaccine effectiveness for the prevention of invasive pneumococcal disease in children in the USA. DESIGN: Matched case-control study. SETTING: Thirteen active surveillance sites for invasive pneumococcal disease in the USA. PARTICIPANTS: Cases were identified from active surveillance and controls were age and zip code matched. OUTCOME MEASURES: Socioeconomic status was assessed at the individual level via parent interview (for enrolled individuals only) and birth certificate data (for both enrolled and unenrolled individuals) and at the neighbourhood level by geocoding to the census tract (for both enrolled and unenrolled individuals). Prediction models were used to determine if socioeconomic status was associated with enrolment. RESULTS: We enrolled 54.6% of 1211 eligible cases and found a trend toward enrolled cases being more affluent than unenrolled cases. Enrolled cases were slightly more likely to have private insurance at birth (p=0.08) and have mothers with at least some college education (p<0.01). Enrolled cases also tended to come from more affluent census tracts. Despite these differences, our best predictive model for enrolment yielded a concordance statistic of only 0.703, indicating mediocre predictive value. Variables retained in the final model were assessed for effect measure modification, and none were found to be significant modifiers of vaccine effectiveness. CONCLUSIONS: We conclude that although enrolled cases are somewhat more affluent than unenrolled cases, our estimates are externally valid with respect to socioeconomic status. Our analysis provides evidence that this study design can yield valid estimates and the assessing generalisability of observational data is feasible, even when unenrolled individuals cannot be contacted.