H1N1 vaccine was safe and effective in young children

VANCOUVER – A novel influenza A (H1N1) vaccine (Panvax H1N1, CSL Limited) yielded strong seroconversion and seroprotection rates in young children, according to findings presented at the 48th Annual Meeting of the Infectious Diseases Society of America.

Pedro Piedra, MD, of the departments of Pediatrics and Molecular Virology and Microbiology at Baylor College of Medicine in Houston, stressed that the H1N1 influenza virus caused the first pandemic of the 21st century.

“A major public health emphasis was placed on the development of an immunogenic and safe monovalent novel H1N1 vaccine,” he said.

The primary aim of the phase-2, multicenter, age-stratified, randomized, placebo-controlled trial was to assess the immunogenicity of the vaccine. The secondary aim was safety.

Trial protocols

There were 227 children aged younger than 3 years and 246 children aged older than 3 years in the final analysis. Participants were randomly assigned to placebo, 7.5 mcg or 15 mcg vaccine in a ratio of 1:4:4. Baseline data were comparable across the three groups, and all injections were delivered intramuscularly.

Vaccinations were administered on days 0 and 21. Blood was drawn from study participants on days 0, 21 and 42.

The primary outcome measure was the percentage of children who achieved seroconversion — which was defined as a > fourfold rise in hemagglutination inhibition — and seroprotection — which was defined as a > 1:40 hemagglutination inhibition titer — 21 days after each vaccine dose.

A 7-day solicited and 21-day unsolicited event diary was used to assess safety.

Day-21 results indicated seroconversion and seroprotection rates of more than 86% of children in the vaccine arms, compared with a 4% seroconversion rate and a 17% seroprotection rate in the placebo arm. Day-42 results indicated more than 98% seroconversion and seroprotection rates in the two vaccine arms and 17% seroconversion and 32% seroprotection among children receiving placebo.

“There was not much difference between the 7.5 mcg and 15 mcg doses,” Piedra said. “Also, if you look at seroconversion by each age group stratification, they are very similar. Age was not a factor in the seroconversion for each vaccine group.”

Piedra said the same was true for seroprotection data as stratified by age.

Fever

Safety profile data indicated that nearly 80% of children had one type of adverse event but that the majority of adverse events were mild and short-lived, according to Piedra. Injection-site pain and redness were the most frequently reported events.

“We included more information for fever [in the trial] because fever is the main adverse event, particularly for children aged 6 months to 3 years,” Piedra said. “The key point here is that you see a dose response by age; the younger children who received the higher vaccine dose had higher rates of fever.”

Piedra said that younger children in the 15-mcg arm also were more likely to experience moderate or severe fever but that most fevers dissipated within 2 days of vaccination.

“Interestingly, we did not see this pattern after the second dose, and we did not see this in older age groups,” Piedra said. – by Rob Volansky

For more information:

• Piedra P. #176. One Dose of CSL 2009 nH1N1 Influenza Vaccine at 7.5 and 15 Micrograms of Hemagglutinin (HA) is Immunogenic and Safe in Children 6 Months up to 9 Years Old. Presented at: the IDSA 48th Annual Meeting; Oct. 21-24, 2010; Vancouver, B.C.

Disclosure:

Piedra reported being a grant investigator with CSL and Sanofi-Pasteur; and being a grant investigator and being on the speaker’s bureau at MedImmune and Roche.

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