In this outbreak, vaccination provided poor protection against varicella, although there was good protection against moderate or severe disease. A longer interval since vaccination was associated with an increased risk of vaccine failure. Breakthrough infections in vaccinated, healthy persons can be as infectious as varicella in unvaccinated persons.

Cases of measles that require hospitalization are a good marker of the burden of clinically severe measles in the United States. Measles hospitalizations routinely are monitored by the National Notifiable Disease Surveillance System (NNDSS). Our objectives were to describe measles hospitalizations reported to the NNDSS in 1985-2002, to use hospital discharge data from independent data sets (the National Hospital Discharge Survey [NHDS] [data available for 1985-1999] and the Health Care Investment Analysts [HCIA] hospital discharge database [data available for 1985-1996]) to provide additional estimates of total measles hospitalizations, and to compare trends in measles-associated hospitalizations. In 1985-2002, a total of 13621 patients with measles reported to the NNDSS were hospitalized (annual average, 757; range, 19-5856 patients). In 1985-1996, a total of 13472 measles hospitalizations were reported from NNDSS, compared with 28047 estimated from the NHDS and 19352 extrapolated from HCIA data. In the NNDSS, the annual total number declined after 1992 to