A 5-year follow-up of antibody response in children vaccinated with single dose of live attenuated SA14-14-2 Japanese encephalitis vaccine: immunogenicity and anamnestic responses.

Out of 98 subjects who had participated in the 2000 JE vaccination campaign, 69 people were enrolled in the tests of 2004 and 2005 for the evaluation of long term immune response of a single dose of live attenuated SA14-14-2 JE vaccine. 89.9% of study subjects (62/69) had maintained a high level of neutralizing antibody until 2004 as their GMT was measured as 133 (Min 11, Max 2991). Forty-four subjects were still positive in 2005, 5 years after JE vaccination, and their neutralizing antibody positive rate was significantly higher than that of 69 age-sex matched unvaccinated control subjects: 63.8% (44/69) vs. 14.5% (10/69) (P<0.05). Twenty-four subjects (Group 1) who were seronegative for neutralizing antibody at the 2005 test were given a second dose for revaccination in 2006. Also 49 seronegative (Group 2) subjects who were enrolled as a control group in 2005 were given one dose of primary JE vaccine in 2006. Seven days after vaccination, seropositive rate was discovered to be 76.5% (13/17) and 168.52 (Min 38, Max 2173) in Group 1, while no seroconversion in Group 2. On the 30th day, seropositive rate and GMT were 82.4% (14/17) and 392.01 (Min 22, Max 2197) in Group 1, while 75.7% (28/37) and 45.72 (Min 12, Max 505) in Group 2, respectively. We observed the persistence of neutralizing antibody of single dose of live attenuated SA14-14-2 JE vaccine, 89.9% after 4 years and 63.8% after 5 years, and a rapid secondary immune response on the seventh day after booster dose among those who had been seronegative in spite of the first dose of vaccine. Single dose of live JE vaccine could be effective to provide a long-term protection in JE endemic area, where natural boosting is quite probable in the vaccinees. However, further studies should be carried out to support whether one dose of live JE vaccine is sufficient for people in JE non-endemic area.