Seroprevalence rate after one dose of varicella vaccine in infants

Background: Live, attenuated varicella vaccine has been used since 1988 in Korea. However, varicella is still prevalent among both vaccinated and unvaccinated individuals, despite a relatively high level of immunization rate up to 80%. A recent report has demonstrated similar to 20% of primary vaccine failure rate after one dose of varicella vaccine using the fluorescent antibody to membrane antigen (FAMA) assay. Methods: The seroprevalence rate was determined using the FAMA and ELISA assays in 67 Korean infants following one dose of varicella vaccine. Positive fluorescence at a serum dilution of 1: 4 or greater was considered as seropositive. Results: The median age at vaccination was 12 months and the post-immunization sera were obtained on average 6.3 months (range 6 weeks-12 months) after vaccination. Among the 67 vaccinated infants, 56 (83.6%) were seropositive by FAMA assay while 30 (44.8%) were seropositive by ELISA. The geometric mean titers (GMTs) of the seropositive vaccinated infants (n = 56) were significantly lower than the GMTs of 9 individuals with a history of varicella (1:17.0 vs. 1:74.7, P = 0.001). Although there were no significant differences in seropositive rates according to intervals, there was a decreasing trend in the GMTs over time among the 56 seropositive recipients (r(2) = 0.154, P < 0.001). Conclusions: These data can be useful for optimizing the immunization strategy against varicella and should be confirmed by a prospective study including a large number of immunized infants. (c) 2010 The British Infection Society. Published by Elsevier Ltd. All rights reserved.