Preliminary data from pediatric influenza A H1N1 vaccine trials encouraging

Immune responses similar to those observed with seasonal influenza vaccine.

Early results from an ongoing pediatric 2009 H1N1 influenza vaccine trial indicated that a single 15 mcg dose of an inactivated, unadjuvanted vaccine may be sufficient to induce a protective immune response among healthy children aged 10 to 17 years, but younger children may need an additional dose.

“The initial results are encouraging. As we had hoped in children, the 2009 H1N1 influenza vaccine is acting just like seasonal flu vaccine,” Anthony S. Fauci, MD, director of the National Institutes of Allergy and Infectious Diseases, said today during a press briefing.

Blood samples drawn from approximately 600 children eight to 10 days after receiving one 15 mcg dose of vaccine (Sanofi Pasteur) revealed robust immune responses as measured by ≥ 1:40 hemagluttinin inhibition titer in the following:

76% of children aged 10 to 17 years;
36% of children aged 3 to 9 years; and
25% of children aged 6 to 35 months.

Fauci emphasized that the lower antibody titers observed among children aged 6 months to 9 years was not unexpected and is similar to that normally observed in children who receive seasonal influenza vaccine. He projected that vaccine recommendations for younger children will most likely include a second 15 mcg dose to be administered 21 days following the initial vaccine.

“Overall this is very good news for the vaccination program both in regard to supply of vaccine, as well as to its potential efficacy,” Fauci said.

Anne Schuchat, MD, director of the Center of Immunization and Respiratory Diseases at the CDC, suggested that health care providers encourage parents of younger children to vaccinate their children with the seasonal influenza vaccine as early as possible.

“Seasonal flu vaccine is already available so parents can start getting children vaccinated now; they don’t need to wait,” Schuchat said. “Once the 2009 H1N1 influenza vaccine is available, it may be possible for them to get both [seasonal and H1N1 vaccines] at the same time depending on the vaccine formulations.”

Schuchat explained that researchers expect that administering inactivated seasonal and H1N1 injections on the same day should be safe based on existing vaccine knowledge, but immune responses to live-attenuated vaccines may be subpar if those are administered concomitantly.

Vaccine availability

These data are the first available regarding 2009 H1N1 vaccine and children; however, Jesse L. Goodman, MD, MPH, director of the Center for Biologics and Research at the FDA, said that results from additional manufacturer trials should be available in the coming weeks.

Health officials projected last week that 3.4 million doses of live-attenuated 2009 H1N1 vaccine should be available in nasal spray formulation by early-to-mid October. Currently, nasal spray is only licensed for healthy children and adults aged 2 to 29 years who are not pregnant, but Schuchat said this is just the beginning of the flow of available vaccines and that additional formulations are expected.

Sanofi Pasteur announced today that the company has received an additional order from the U.S. Department of Health and Human Services to produce bulk antigen equivalent to 27.3 million doses based on 15 mcg of antigen per dose. To date the company has committed to providing a total of 75.3 million doses of influenza A (H1N1) 2009 monovalent vaccine to the U.S. government. – by Nicole Blazek