Variants within the "a" determinant of HBs gene in children and adolescents with and without hepatitis B vaccination as part of Thailand's expanded program on immunization (EPI)
A. Theamboonlers et al., Variants within the "a" determinant of HBs gene in children and adolescents with and without hepatitis B vaccination as part of Thailand's expanded program on immunization (EPI), TOH J EX ME, 193(3), 2001, pp. 197-205
A total of 2229 children selected from five distinct areas of Thailand were
screened for HBs antigen (HBsAg) by ELISA. Out of 51, forty-nine HBsAg-pos
itive children were further examined for HBV-DNA by the polymerase chain re
action, utilizing the region of the hepatitis B Virus (HBV) genome encoding
the major antigenic epitopes of hepatitis B surface antigen. Direct automa
ted sequencing of the "a" determinant region revealed 11 of 49 children to
display variable mutations. The vaccinated and nonvaccinated children had a
mino acid variants clustered between residues 120 and 160. Mutations betwee
n residues 120 and 160 were found at higher frequency in the vaccinated gro
up (4/ 13; 30.8%) than in the nonvaccinated group (7/36; 19.4%), but this w
as not statistically significant. Infections with new HBV variants are cont
racted either vertically or horizontally within the group having received t
he vaccine, a finding confirmed by the presence of amino acid substitutions
critical for immune escape. Hence, neither vaccine nor IgG; has any appare
nt effect on those variants and the children turn into HBV carriers. Howeve
r, the current vaccination program still efficiently protects perinatal tra
nsmission of HBV and unless long term studies lead us to conclude otherwise
, inclusion of the variant strain(s) into a new vaccine formulation is not
deemed necessary.