HK’s recent history of `Twin Peaks’ of influenza– Credit Flu Express
Although there are some subtle signs that the worst of Hong Kong’s severe flu season may be waning, school and work schedules are just now returning to normal following the Lunar New Year Holiday, and concerns run high that a second surge of flu may ensue.
With 310 flu-related deaths recorded since early January, this year’s flu outbreak is already more than twice as deadly as last year, with the potential for seeing several more months of activity.
Complicating the situation, Hong Kong often sees a biphasic or `double peaked’ flu season, as the chart at the top of this post , and the following 2008 PLoS One research paper illustrates:
Julian W. Tang,1,* Karry L. K. Ngai,1 Wai Y. Lam,1 and Paul K. S. Chan1,2
Hong Kong is a subtropical region of almost 7 million people, 95% of whom are ethnic Chinese, with a mean temperature of 24°C and mean relative humidity of 79% . It lies geographically in the Northern hemisphere, and its influenza season occurs during February–April, sometimes with a second peak during June–August, each year.
In contrast, other Northern hemisphere countries usually have a more extended influenza season from November to March/April, whereas the influenza season of Southern hemisphere countries usually occur from May to September , .
Hence, Hong Kong may be unique in that its biphasic influenza seasonality seems to straddle those of the Northern and Southern hemisphere countries, making the molecular epidemiology of its circulating influenza viruses of great interest. In addition, Hong Kong and Southern China have been referred to as the ‘epicenter’ for new influenza A viruses with pandemic potential for over 25 years now . For all of these reasons, any investigation of the underlying basis for influenza seasonality may benefit greatly from a study of influenza viruses isolated from Hong Kong.
Hong Kong officials are worried enough they are making special arrangements to purchase a quantity of the recently revised Southern Hemisphere vaccine for use in a second wave of vaccination for high risk individuals, as announced recently in New flu vaccine ready by April.
This update from Hong Kong’s CHP.
The Centre for Health Protection (CHP) of the Department of Health today (March 2) reported the latest surveillance data of the winter influenza season, and again urged the public to heighten vigilance and get vaccinated early against seasonal influenza.
"As most schools resumed after the Lunar New Year, we today issued letters to kindergartens, child care centres and primary and secondary schools as well as special schools to alert them to the current influenza activity, which remains at a high level and is expected to remain so for some time. Continued vigilance is warranted," a spokesman for the CHP said.
Schools should continue to actively check the body temperature of all students every day to identify those with fever who should not attend school till 48 hours after it subsides. Staff with respiratory illnesses should also refrain from work," the spokesman added.
Schools may refer to the CHP's Guidelines on Prevention of Communicable Diseases (LINK) for further information.
Regarding severe cases, from noon yesterday (March 1) to noon today, six additional cases of influenza-associated admission to intensive care units or death (including three deaths) among adults aged 18 or above have been recorded under the enhanced surveillance in collaboration with public and private hospitals reactivated since January 2 and an additional death was recorded among previously reported cases, bringing the total to 421 (310 deaths) so far. Among them, 403 were A(H3N2), two were A(H1N1)pdm09, seven were A pending subtype and nine were B. In the last winter season in early 2014, 266 (133 deaths) were filed.
Meanwhile, no additional cases of severe paediatric influenza-associated complication or death among children aged under 18 have been reported since yesterday via the ongoing reporting system and the total this year hence remains at 17 (one death) and all were A(H3N2). In 2014, 27 cases (four deaths) were filed.
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Although the two viruses aren’t really comparable, this year’s seasonal flu death toll has now exceeded the number killed in Hong Kong by SARS (n=299) in 2003 (see SARS and Remembrance).
The difference being that SARS infected fewer than 2000 people in Hong Kong while racking up that toll, while influenza has likely infected hundreds of thousands.
While other areas in Europe, India, and Asia are seeing high levels of seasonal influenza activity right now, we always pay special attention to Hong Kong’s flu season. Simply because it has excellent surveillance, and its proximity to southern China makes its a credible place to look for the emergence and spread of novel flu viruses.