August 13, 2012 — Seropositivity to hepatitis A vaccine given in 2 doses before age 2 years persists until at least age 10 years for most children, whether or not there was exposure to maternal anti-hepatitis A virus (anti-HAV) at the time of vaccination, according to a study published in the August issue of Hepatology.
The number of cases of hepatitis A infection in the United States has decreased markedly since the early 1990s, when routine vaccination of children beginning at 12 months of age began. Persistence of seropositivity is important to monitor because infection after childhood often produces more severe symptoms than earlier infection, and exposure to maternal antibodies could have dampened prolonged response to vaccination.
Umid M. Sharapov, MD, from the Division of Viral Hepatitis, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues assessed hepatitis A seropositivity in 3 cohorts of Alaskan children, most of whom were Alaskan natives or American Indians. Before 1996, when limited vaccination began in this population, hepatitis A was hyperendemic.
The 197 young children included in the trial were randomly assigned to receive vaccine at 6 and 12 months, 12 and 18 months, and 15 and 21 months. The researchers measured seropositivity of at least 10 mIU/mL at 1 and 6 months of age and at 3, 5, 7, and 10 years. The children were randomized for maternal antibody status.
Most of the children remained seropositive at age 10 years. The exceptions were 7% of children vaccinated at 6 and 12 months whose mothers were anti-HAV-negative, 11% of children vaccinated at 6 and 12 months whose mothers were anti-HAV-positive, and 4% of children vaccinated at 15 and 21 months whose mothers were anti-HAV-negative.
The children with the highest geometric mean concentration (GMC) of antibodies had been vaccinated at the oldest ages and were not exposed to maternal antibodies (97 mIU/mL; 95% confidence interval [CI], 71 - 133 mIU/mL).
The children in the youngest cohort whose mothers were anti-HAV-positive had the lowest GMC (29 mlU/mL; 95% CI, 20 - 40 mIU/mL).
"Our finding that the GMCs of anti-HAV were higher in those infants starting the vaccination series after 12 months of age supports current CDC/[Advisory Committee on Immunization Practices] guidelines for the routine administration of hepatitis A vaccine to all children in the United States beginning at the age of 12 months," the researchers conclude. They plan to follow-up the children for at least 5 more years.
Limitations of the study, the authors write, are the loss of some children to follow-up, focus on a single population group, and use of the minimum antibody titer to define seropositivity. They point out that the minimum antibody titer to confer immunity to hepatitis A is not known.
The authors have disclosed no relevant financial relationships.
Hepatology. 2012;56:516-522. Abstract
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