Summer flu peak worse than winter, study finds
The summer influenza A peak has surpassed the winter peak in recent years, raising the possibility that global warming is changing the behaviour of the virus, researchers say.
A virologist has also warned that higher temperatures, such as those being experienced by Hong Kong, increase the chance of a mutation.
A study by Chinese University and the Observatory found that influenza A, including swine flu, was more active when the temperature was above 24 degrees Celsius or below 21, leading to the summer and winter peaks.
Chinese University virologist Paul Chan Kay-sheung said the researchers found the activity of the virus was very low between 21 and 24 degrees, and there were two peaks - one between February and March, and one during June and July each year.
The study used data on the number of influenza admissions at Prince of Wales Hospital and the daily temperature and relative humidity recorded in Sha Tin, where the hospital is located, between 1997 and 2006.
Only cases requiring hospital treatment were looked at as the study was focused on severe cases that put pressure on the medical system, Professor Chan said.
During the early part of the study, from 1998 to 2000, the winter/spring peak of influenza A was higher than the summer peak.
But by 2004-2006 the summer peak had overtaken it, Professor Chan said.
The senior scientific officer (climatological services) at the Observatory, Mok Hing-yim, said temperatures had risen by less than 1 degree due to global warming during the period of the study.
'It is too early to say that global warming has led to a change in the influenza activity as infection is determined by a number of factors other than weather, including people's daily habits and vaccination ' Mr Mok said.
With more hot days expected, Professor Chan said, the chance of a virus mutating was higher.
'Experts find that mutation of the flu virus is more active in tropical regions, where the period of a higher level of influenza activity is longer,' he said. 'So, the more hot days and the higher temperatures a place has, the higher the chance of a virus mutation.'
Professor Chan said it was reasonable to expect a swine flu peak in the summer. 'Swine flu is a kind of influenza A. So it is reasonable to believe that swine flu will become active during the summer,' he said. 'And as many experts have already stated, it is very likely that it will become a seasonal flu.'
Professor Chan called for special attention to be paid to the timing of vaccinations as well as the duration of the protection they gave.
'November to December is the best period for vaccination since its effectiveness will be decreased if it is administered too early or too late,' Professor Chan said.
He added that as swine flu was a new virus, people should have inoculations against it once a vaccine was available.
