[Immunogenicity of additional varicella vaccination 3-5 years after the initial vaccination]

Additional varicella vaccination was carried out targeting 16 subjects who had immune adherence hemagglutination (IAHA) seroconversion following the initial varicella vaccination and did not contract breakthrough varicella after the initial vaccination. The median ages at the initial and additional vaccination were 2.1 (1.1-6.9) years old and 6.1 (4.4-10.5) years old, respectively. The mean interval between the initial and additional vaccination was 4.0 (3.2-5.2) years. IAHA and glycoprotein-based enzyme-linked immunosorbent assay (gpELISA) antibody titers were measured just before and 4-6 weeks after the additional vaccination. Side reaction was surveyed at four weeks after the additional vaccination, and compared with the results at the initial vaccination. IAHA and gpELISA seroconversion rates at the initial vaccination were 100% and 88% respectively. Prior to the additional vaccination, IAHA antibody titers significantly decreased in 50% of the subjects, and became negative in 38% of the subjects. On the other hand, a significant increase in IAHA antibody titers was observed in 25% of the subjects, and this is assumed to be the result of a subclinical infection after the initial vaccination. The positive rate of both antibodies after the additional vaccination was 100%, the mean IAHA antibody titer (Log2) after the initial/additional vaccination in seropositive subjects was 4.6/6.5, and the mean gpELISA antibody titer (Log10) was 2.3/4.0. The mean IAHA and gpELISA antibody titers were higher after the additional vaccination than after the initial vaccination (p < 0.01, p < 0.01). This is considered to be the booster effect due to the additional vaccination. At 0-2 days after the additional vaccination, a rash at the injection site was observed in 56% of the subjects, higher than the incidence after the initial vaccination (13%) (p < 0.05), but no severe systemic side reactions were observed at either the initial or the additional vaccination. In conclusion, an additional varicella vaccination 3-5 years after the initial vaccination is thought to have greater immunogenicity and is considered effective.