NEW YORK (Reuters Health) – Over time, vaccine-induced rubella antibody levels decline and seronegativity rates rise, leaving children vulnerable to infection, public health officials report.

“Because rubella is a highly epidemic disease, vigilance will be required to assure continued elimination,” Dr. Charles W. LeBaron of the Centers for Disease Control and Prevention, Atlanta and colleagues caution in the September 15 issue of the Journal of Infectious Diseases.

All states in the US require a second measles-mumps-rubella vaccine dose (MMR2), some at kindergarten entry and others at middle-school entry. In Wisconsin, where proof of MMR2 is required at both time points, the researchers analyzed pre- and post-vaccination serum samples collected in 1994-1995 from 307 children given MMR2 at ages 4 to 6 years and a comparison group of 306 children who received the booster at ages 9 to 11. The endpoint was persistence of antibodies at age 17.

The authors point out that at MMR2 administration, it had been 4 years since the first dose of the vaccine for the younger children and 10 years for the older group.

Before MMR2, the kindergarten children “had higher overall antibody levels” and a significantly lower incidence of negative titers: 9.4% vs 24.5% in the middle-school group.

After MMR2, 62% of the younger group and 66% of the older group showed a fourfold increase in titer, with the incidence of seronegativity reduced to less than 1%.

By age 17, both groups had antibody levels higher than their pre-MMR2 titers. However, the investigators found, the proportions with negative titers in both groups had fallen back to pre-MMR2 levels: 9.7% in the kindergarten group and 20.6% in the middle-school group.

They note that at each serum specimen collection and age, the younger group had significantly higher antibody levels than the older group, despite a much longer interval since the second dose, the researchers note.

“The possibility of rubella susceptibility among those whose titers have waned cannot be ruled out,” the authors warn.

They conclude, “Because rubella is a highly epidemic disease, vigilance will be required to assure continued elimination.”

Reference:
J Infect Dis 2009;200:888-899.