The A/H1N1 flu poses a challenge for China's public health system. Medical experts are advising high-risk groups get protection.

The Ministry of Health defines high-risk groups as pregnant women, overweight people, children under five, and the elderly above 65.

People with chronic diseases and weak immune systems are more vulnerable to developing serious cases of A/H1N1 flu.

Doctors also warn young and middle-aged people to be specially cautious of the rapid reproduction of the virus, saying if condition worsens within a day, they must go to hospital.

Vaccines are crucial in the fight against A/H1-N1 flu. Mass vaccinations have started in many provinces around China. Among the first batch to receive vaccine, only 200 people suffered minor side effects, such as low fever and local muscle pain.

Doctors also recommend a separate injection of both A/H1-N1 flu vaccine and the seasonal flu vaccine.

But certain people should not get the A/H1-N1 flu vaccine. They are children under three, people with an egg allergy, heart disease, pulmonary heart disease, diabetes, or other diseases in their acute stage.

(CCTV October 30, 2009)