More than 100 people across China have been infected with H1N1 flu since Friday, a clear signal the peak season has begun for the potentially deadly virus, Zeng Guang, a senior epidemiologist at the Chinese Center for Disease Control and Prevention, warned Sunday.

The mass outbreak among mainly students has lead to the closure of more than 20 schools stretching from the Guangxi Zhuang autonomous region in the south to Ningxia Hui autonomous region in the northwest, just one week after the start of the new school term.

"The recent clusters of school outbreaks are just the start of the peak season, which will feature widespread infections," Zeng told China Daily.

"The virus will definitely sicken more people, with new infections rising more quickly than before, though no mutations have so far been detected.

"The total cases nationwide will soon double to 10,000."

The Chinese mainland has reported 4,415 cases of H1N1 influenza, with 3,577 people having recovered, the Ministry of Health said on Friday, adding that no one had died.

H1N1 would now begin to spread to small cities, remote and rural areas, and among organizations like the army and factory workers during the fall and winter months, in line with the seasonal flu, he explained.

Most infections have been in the larger cities, with one person still in critical condition in Shanghai.

By noon on Sunday, 67 people were confirmed to have contracted the virus at four universities in Langfang, Hebei province, according to the provincial health department.

Meanwhile, Xinhua News Agency reported the virus entered two regions for the first time over the weekend.

Xinjiang Uygur autonomous region on Saturday confirmed its first patient, a middle school student. The Ningxia Hui autonomous region, also in the northwest, reported its first infection the same day.

A total of 30 H1N1 cases were reported in schools in Qinghai, Fujian, Sichuan and Shaanxi provinces.

In Chongqing, three schools reported 27 confirmed cases.

In Shandong province, nine students from Wangcun Middle School in Jimo were confirmed infected. The students were in stable condition, the provincial health department said.

In addition, 19 students at a secondary school in Huizhou, southern Guangdong province, were confirmed as infected, a spokesman with the municipal health bureau said.

"The first flu patient at the Huizhou Agricultural School, a boy student, is being quarantined at home," the spokesman said. "He has no fever or other flu symptoms now and the people who have close contact with him are in good physical condition."

The spokesman said the remaining 18 students are in quarantine in hospital, and only three have so far shown any symptoms.

Schools where a student has been confirmed as infected are usually closed.

Zeng said: "Local authorities could temporarily close schools based on the situation, but I don't recommend totally closing schools as a precaution." At the moment people need education on flu prevention and control, like having the seasonal flu shot, rather than panicking, he suggested.

The Ministry of Health is expected to release its inoculation plan around Sept 15, when the first 7.3 million doses of the vaccine will be ready, Zeng said.

"Safety is the top priority and cannot be compromised by urgency," said Liang Wannian, deputy director of the ministry's contingency office.

The domestically-developed vaccine, which can protect people aged three and above, will not be sold to the general public, but is to be reserved by the State.

Health Minister Chen Zhu has said the government will prepare 65 million doses by the year's end. There are 10 designated companies in China producing the vaccines.

Vivian Tan, press officer of the World Health Organization (WHO) Beijing Office, declined to comment on whether vaccines for just 5 percent of the county would be sufficient.

"WHO does not recommend a specific percentage of people be vaccinated in each country. It's important that we don't see the vaccine as a cure-all and neglect other ways of prevention," she told China Daily.

"The vaccine is a critical new tool in preventing the spread of H1N1. But realistically, the supply - 5 percent or otherwise - will not be able to match the demand in the initial months. Thus there is a need to identify priority groups for vaccination," she said.

(Xinhua News Agency September 7, 2009)