The A/H1N1 influenza virus is responsible for nearly 80 percent of China's total flu infections and most of the mass cases occurred in schools, according to a senior official with the Ministry of Health (MOH).

"As the weather keeps getting colder, many regions are entering the traditional period of possible flu outbreak, and prevention and control work is becoming tougher," Liang Wannian, vice director of the health emergency office under the MOH, said Thursday during an online interview with the official website of the Chinese government.

According to Liang, as of Wednesday, a total of 1,502 mass cases were reported in 31 provinces, municipalities and autonomous regions of the Chinese mainland and 96.4 percent occurred in schools.

Liang said the country would act faster in providing vaccines for more people as it was still the most effective way to protect vulnerable groups and keep patients' illness situation from deteriorating.

On Wednesday Beijing reported an A/H1N1 death case of a university student, also the fourth on the Chinese mainland.

Liang revealed that, based on clinical experiments, at least 85 percent of people receiving the vaccine would get protection from the virus and the effectiveness duration would last till this winter or next spring.

So far the side effects of the vaccine had been mostly slight, such as temporary fever and exhaustion, and the benefits from receiving the vaccine were "far greater" than harms.

Statistics from the ministry show that the Chinese mainland had reported 42,009 confirmed cases of the A/H1N1 flu by 3 p.m. Wednesday.

A total of 30,854 patients had recovered. Twenty-two of 66 patients in serious conditions had been cured, the ministry said.