A study done by local experts showed that the magnitude of influenza A's summer peak has become higher in recent years in Hong Kong, according to a press release the reporter received on Friday.

The Chinese University of Hong Kong and the Hong Kong Observatory jointly studied the relationship between weather and influenza activity in Hong Kong.

The study analyzed the information of the laboratory-confirmed influenza A and B cases admitted to the Prince of Wales Hospital and the Observatory's weather data from 1997 to 2006.

The study found that, in general, there were more influenza A than influenza B-associated admissions in Hong Kong. The two types of influenza showed a different relationship with weather conditions.

Influenza A had two seasonal peaks in Hong Kong which occurred respectively in winter and spring months, i.e. February to March and summer months, i.e. June to July. Influenza B also had a clear winter and spring peak, but its activity during the summer months was more variable.

It was found that, for influenza A, a shift in the relative magnitude of the two seasonal peaks was observed. In 1998 to 2000, the magnitude of the winter and spring peak of Influenza A was higher than the summer peak. In 2004 to 2006, the magnitude of the summer peak had become larger than the winter and spring peak.

In view of the above results, Professor Paul Chan Kay-sheung of the Department of Microbiology of the university remarked that the emergence of a second seasonal peak of influenza A activity in summer in Hong Kong, particularly its recent trend of increase in magnitude.

Chan ascribed this phenomenon to global warming and that influenza A virus has become more heat-resistant.

According to the study, flu A virus was less active between 21 to 24 degree Celsius. As it became warmer in winter with more days reached this temperature range, fewer flu case occurred. While the warm period in summer prolonged with more days over 24 degree Celsius, the magnitude of flu A rose.

As the new strain disease, influenza A/H1N1, which is spreading among different countries and regions, belongs to the influenza A type, Chan expected the magnitude of the new virus will become stronger during June and July.

Besides, Chan called for special attention on the timing of vaccination as well as its duration of protection, saying that November to December is the best period for vaccination since its effectiveness will be decreased if it is administered too early or too late.

Mok Hing-yim, Senior Scientific Officer of the Hong Kong Observatory expected that the weather conditions in Hong Kong in this summer would be near normal. The public is advised to pay attention to personal and public hygiene in the coming months.

(Xinhua News Agency June 19, 2009)