Shares of Chinese drug makers that produce medication for influenza have made strong gains, as the ailment overtakes Covid-19 as the major pandemic ravaging the country. The Hong Kong-traded stock of Yichang HEC Changjiang Pharmaceutical, which has a 90 per cent market share of the flu medicine oseltamivir in China, jumped 7.1 per cent for its biggest gain in a month on Tuesday, extending an almost 3 per cent advance last week. It dropped back 2.5 per cent to HK$7.90 on Wednesday. Other licensed makers of oseltamivir and flu vaccines have also been riding the wave. ApicHope Pharmaceutical rose to a record high of 48.69 yuan in Shenzhen this week, while Hualan Biological Bacterin is set for two straight weeks of gains, taking its rally to 10 per cent since February 17. The buying spree has been spurred by a spike in flu cases in mainland China, which prompted some primary schools in Beijing, Shanghai and Zhejiang province to suspend classes last week. The latest data from China’s disease control centre shows that flu cases have recently overtaken Covid-19 infections , although exact numbers are unavailable. “It’s a short-term trade and the momentum may not last too long,” said Dai Ming, a fund manager at Huichen Asset Management in Shanghai. “Flu is a seasonal disease and demand for the relevant drugs is no match for that for Covid , which the country concentrates all the resources on to fight against.” Oseltamivir has been out of stock in drug stores in big cities including Beijing and in online pharmacies in the last week or so, as people rushed to stockpile the medicine amid signs of a massive outbreak. Drug producers including Brightgene Bio-medical Technology, responding to queries from investors on the stock exchange’s online platform, said that they would ramp up production to meet the rising demand. As recent history shows, investors chasing the trend risk being burned. When China abruptly removed all its Covid-19 restrictions in November, traders flocked to snap up shares of companies that make drugs for common cold , rapid antigen test kits and masks. The frenzy cooled after coronavirus infections ebbed in January, sending the stocks plummeting. For example, Shijiazhuang Yiling Pharmaceutical, which makes Lianhua Qingwen, a herbal capsule officially recommended by the government to treat Covid-19, has tumbled 41 per cent from a December high. A strain known as H1N1 accounts for about 70 per cent of the flu infections in China, according to official data. The incubation period typically runs between one and three days and most cases are mild, with sufferers showing symptoms such as fever, coughing and sore muscles, similar to Covid-19. HEC Changjiang Pharmaceutical is expected to post net income of 551.7 million yuan (US$79.7 million) for last year, rebounding from a loss of 587.7 million yuan in 2021, according to Bloomberg data. Its results are due on March 21.