The US Food and Drug Administration on Tuesday approved vaccines against the A/H1N1 flu virus, which will be distributed nationally within the next four weeks after the initial lots become available.

"Today's approval is good news for our nation's response to the2009 H1N1 influenza virus," said FDA Commissioner Margaret A. Hamburg. "This vaccine will help protect individuals from serious illness and death from influenza."

The vaccines are made by CSL of Australia, US-based MedImmune LLC, Novartis of Switzerland and France's Sanofi Pasteur Inc. All four firms manufacture the A/H1N1 vaccines using the same processes, which have a long record of producing safe seasonal flu vaccines.

Based on preliminary data from adults participating in multiple clinical studies, the vaccines induce a robust immune response in most healthy adults eight to 10 days after a single dose, as occurs with the seasonal flu vaccine.

Clinical studies under way will provide additional information about the optimal dose in children. People with severe or life-threatening allergies to chicken eggs, or to any other substance in the vaccine, should not be vaccinated, the FDA said.

In the ongoing clinical studies, the vaccines have been well tolerated. Potential side effects of the A/H1N1 vaccines are expected to be similar to those of seasonal flu vaccines, it added.

For the injected vaccine, the most common side effect is soreness at the injection site. Other side effects may include mild fever, body aches, and fatigue for a few days after the inoculation.

For the nasal spray vaccine, the most common side effects include runny nose or nasal congestion for all ages, sore throats in adults, and -- in children two to six years old -- fever.

(Xinhua News Agency September 16, 2009)