Rubella immunity levels in the United States population: has the threshold of viral elimination been reached?

After the 1989-1991 rubella resurgence, rubella vaccination efforts targeted children and women of childbearing age. Utilizing National Health and Nutrition Examination Survey data collected during 1988-1994 and 1999-2004, we assessed whether US levels of rubella seropositivity are consistent with rubella elimination and whether changes are consistent with immunization efforts. Serum samples with rubella antibody levels > or =10 IU tested by rubella immunoglobulin G enzyme immunoassay were considered to be positive. In 1999-2004, the overall age-adjusted rubella seropositivity level was 91.3% (95% confidence interval [CI], 90.5%-92.1%), a significant increase from 88.1% (95% CI, 86.9%-89.1%) in 1988-1994 (P<.001). Among children, seropositivity was highest in children 6-11 years of age (96.2%), followed by adolescents 12-19 years of age (93.7%). Both groups showed significant increases in immunity levels, in comparison with those in 1988-1994 (P<.001). Among adults, seropositivity among women increased (from 88.9% to 91.5%; P=.015), and there was no change among men (from 87.8% to 88.0%; P=.84). In 1999-2004, population rubella immunity levels were at or above the modeled threshold for elimination of rubella virus transmission. Increases in immunity levels are consistent with vaccination efforts.