NEW YORK (Reuters Health) – H1N1 antibody levels remain high in children a year after immunization with a monovalent adjuvanted pandemic swine influenza vaccine, a UK team reports in Clinical Infectious Diseases online January 19.

Furthermore, “It is safe to administer trivalent seasonal influenza vaccine to children who received a 2-dose regimen of the pandemic influenza vaccines used in the United Kingdom in 2009, and this increased children’s antibody levels against the H1N1 component of the vaccine,” the authors report.

Dr. Saul N. Faust, with the University Hospital Southampton NHS Foundation Trust, and colleagues explain that in 2009, they compared the safety and immunogenicity of two pandemic monovalent influenza vaccines — a nonadjuvanted cell culture-derived whole-virion vaccine and an AS03-beta adjuvanted egg culture-derived split-virion vaccine — in 943 children aged 6 months to 12 years old. Subsequently, concerns arose about the immunogenicity of the seasonal trivalent influenza vaccine (TIV) in children previously given monovalent pandemic vaccine.

For the current follow-on study, the team investigated H1N1 antibody persistence at 1 year and assessed the immunogenicity and reactogenicity of a TIV dose in 323 children from the original study who had received two doses of either monovalent vaccine.

Rates of antibody persistence at a titer of at least 1:40 were 100% with the adjuvanted split-virion vaccine and 32.4% with the whole-virion vaccine in children younger than 3, the investigators found. Corresponding rates in older children were 96.9% versus 65.9%.

A dose of TIV was given to 302 of the children, and all had a protective immunogenic response. The vaccination was well tolerated, the authors report, but reactogenicity in children over 5 years of age was slightly higher among those originally given the adjuvanted vaccine.

As well as demonstrating the safety of TIV vaccination in this setting, Dr. Faust and colleagues conclude, “This study provides serological evidence that a 2-dose regimen of vaccination with an AS03-beta adjuvanted pandemic influenza vaccine may be sufficient to maintain protection across 2 influenza seasons.”

From a public health perspective, they suggest, “Pandemic planners may consider initially administering a single dose of adjuvanted pandemic vaccine to allow higher population coverage from limited dose supply, followed by a booster dose in the next season if the same strain is circulating.”

SOURCE:

H1N1 Antibody Persistence 1 Year After Immunization With an Adjuvanted or Whole-Virion Pandemic Vaccine and Immunogenicity and Reactogenicity of Subsequent Seasonal Influenza Vaccine: A Multicenter Follow-on Study

Clin Infect Dis 2012.