The U.S. Food and Drug Administration has approved four vaccines against the 2009 H1N1 influenza virus. The initial lots of the vaccines are expected to become available in a month’s time.

The four vaccines approved are made by CSL Limited, MedImmune LLC, Novartis Vaccines and Diagnostics Limited, and Sanofi Pasteur Inc.

It was only a few days ago that the National Institute of Allergy and Infectious Diseases (NIAID) announced the preliminary data from two vaccine trials involving 2,800 participants above the age of 18. The vaccines were well tolerated, and produced robust immune response in 8-10 days after vaccination. The robust immune response was seen with just one dose of 15 microgram-vaccine.

The most common side effect seen in volunteers receiving the vaccine was soreness at the injection site. Other side effects that people may experience would be mild fever, body aches, and fatigue for a few days after the inoculation.

All the four companies that have got the FDA approval to manufacture the H1N1 vaccines will employ the same processes that are used for producing seasonal influenza vaccines. According to the FDA and the European Medicines Agency, the safety and level of protection offered by a vaccine will remain unchanged when a new virus strain is inserted in an influenza vaccine.

The FDA cautions that people with severe or life-threatening allergies to chicken eggs, or to any other substance in the vaccine, should not be vaccinated.

According to the FDA, all the four vaccines approved will undergo the same rigorous FDA manufacturing oversight, product quality testing and lot release procedures that apply to seasonal influenza vaccines.

The trials have been done only on adults and the vaccine is currently aimed only for them. However, trials are under way to study the safety and immune response of the vaccine in children and pregnant women.

According to the FDA, these clinical studies will provide additional information about the optimal dose in children. The recommendations for dosing will be updated if indicated by findings from those studies. The findings are expected in the near future.