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Three Studies Demonstrate the Safety and Efficacy of Pandemic H1N1 Flu Vaccine

Results are in from studies in the U.S., China, and Hungary.

An estimated 100 million doses of 2009 pandemic influenza A/H1N1 flu vaccines have been administered worldwide since September 2009. Three new reports, containing data previously available only to regulators, provide important information on the safety and efficacy of these vaccines. All vaccines used in these studies were inactivated injected vaccines, produced from a single H1N1 strain recommended by the World Health Organization.

In a randomized U.S. study, 1300 healthy people received one of three formulations of H1N1 vaccine or placebo. At baseline, 20% to 30% of adults and relatively few children had protective levels of H1N1 antibody; 21 days after vaccination, seroprotection rates were 92% to 100% in adults and 45% to 69% in children.

Chinese investigators randomized nearly 13,000 people to receive two doses (21 days apart) of one of eight H1N1 vaccine formulations or placebo. At baseline, few participants had protective H1N1 antibody levels; 21 days after first vaccination, seroprotection rates were 56% to 88% in children younger than 12 and 54% to 98% in older people. After second vaccination, seroprotection rates rose to 93% to 99% and 83% to 100%, respectively.

In Hungary, researchers randomized 355 adults without detectable H1N1 antibodies to receive single injections of a low-dose H1N1 vaccine, with or without simultaneous trivalent seasonal flu vaccination. After 21 days, seropositivity rates were about 70% in both groups.

In the two placebo-controlled studies, seroprotection rates essentially were unchanged in placebo recipients, and low-dose immunizations generally were as effective as higher doses in all but the oldest adults. In all three studies, adverse effects were mild and consisted primarily of injection-site tenderness and low-grade fevers.

Comment: Taken together, these studies suggest that various H1N1 vaccines, given according to current recommendations (1 dose for adults and 2 for children), are safe and effective and that a low-dose immunization strategy can optimize vaccine distribution without compromising efficacy. Perhaps these reports will quell the skepticism and fear with which many patients have greeted the rapid deployment of these novel vaccines.

— Bruce Soloway, MD

Published in Journal Watch General Medicine January 21, 2010

Citation(s):

Plennevaux E et al. Immune response after a single vaccination against 2009 influenza A H1N1 in USA: A preliminary report of two randomised controlled phase 2 trials. Lancet 2010 Jan 2; 375:41.

Liang X-F et al. Safety and immunogenicity of 2009 pandemic influenza A H1N1 vaccines in China: A multicentre, double-blind, randomised, placebo-controlled trial. Lancet 2010 Jan 2; 375:56.

Vajo Z et al. Safety and immunogenicity of a 2009 pandemic influenza A H1N1 vaccine when administered alone or simultaneously with the seasonal influenza vaccine for the 2009–10 influenza season: A multicentre, randomised controlled trial. Lancet 2010 Jan 2; 375:49.

Reader Remarks:

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• H1N1 Vaccine
  M G Mansour, Ain Shams University, 22 Jan 2010 5:35 PM EST
  i wonder about the Pandmrix vaccine distributed in the developing countries like Egypt. Is there any study prove its safety.... [more]
• Infuenza A H1N1 vaccination
  Nebojsa Rajic, 9 Feb 2010 4:17 PM EST
  I hope that authors of those studies will track in follow up their patients (especially children) in 10 to 20... [more]