(Yicai) Aug. 19 -- The number of influenza cases in China soared four-fold in June from a year earlier, according to the latest official data.

Influenza, including adenoviruses, resulted in 315,000 infection cases in June, according to recent data from the Chinese Center for Disease Control and Prevention.

Summer is not the traditional peak season for influenza, as it typically spreads in fall, winter, and spring, experts said, adding that this summer's spike in cases suggests that the seasonal pattern of the flu may have been disrupted.

According to experts, the situation is even more complicated than it seems because many people contract influenza and Covid-19 at the same time.

International pharmaceutical giants, such as Pfizer, BioNTech, Moderna, and Novavax, have invested in the research and development of combined vaccines for Covid-19 and influenza but have not succeeded. However, Chinese peers have not followed this trend.

"Chinese pharmaceutical firms have almost halted the development of Covid-19 vaccines because it has become unprofitable," a scientist involved in developing a combined Covid-19-flu vaccine told Yicai. "Overall, they tend to be relatively cautious and wait to see if foreign companies succeed abroad first."

The scientist believes that it may still take some time before a combined Covid-19 and flu vaccine is developed because of the many factors to consider, such as the actual demand for the product and the continuous Covid-19 mutations.

Without a combined vaccine, people can still use a quadrivalent influenza vaccine, as the overall Covid-19 virulence has weakened, the scientist said. Healthy adults who have already been infected with Covid-19 may no longer need to receive Covid-19 vaccine, while vulnerable groups may consider vaccination.

Editor: Futura Costaglione