Avian Flu Diary: Hong Kong Declares End To Winter Flu Season

Hong Kong's 9 Flu Seasons In Past 5 Years

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After 12 long weeks Hong Kong's CHP has declared the end to their severe (Influenza B) winter flu season - one that as claimed at least 384 lives - while reminding the public to continue to be vigilant about flu hygiene.

Unlike most of the world - which only generally deals with one (winter) flu season each year - Hong Kong is notable for having Biphasic or `double peaked’ flu season, with their heaviest activity generally from February–April and a (usually) less severe season in mid-to-late summer (cite).

As the chart above illustrates, after a very mild winter epidemic in 2017 - after only a few week's break - Hong Kong was hit by an unusually severe and lengthy `second' (H3N2) flu epidemic in the summer, providing them with two significant back-to-back outbreaks.

While they will hopefully have more of a respite before the next epidemic arrives, Hong Kong learned a powerful lesson from SARS in 2003 (see SARS And Remembrance, and is constantly on guard against the next public health threat.

Continued hygiene against respiratory diseases urged beyond winter influenza season

The Centre for Health Protection (CHP) of the Department of Health today (April 4) announced the end of the winter influenza season. Members of the public are however advised to continue to maintain personal, hand and environmental hygiene against respiratory diseases.

"Hong Kong entered the winter influenza season in early January this year. The influenza activity peaked in mid-February and has started to decrease notably since early March. The local influenza activity returned to the baseline level in late March. This season lasted for about 12 weeks from the week of January 7 to the week ending March 31.

"The predominating virus of this winter influenza season has been influenza B. Epidemiological experience shows that children are relatively more affected in seasons with a predominance of influenza B virus, and this was reflected by the large number of outbreaks of influenza-like illness (ILI) in schools in this season," a spokesman for the CHP said.

According to the latest surveillance data, the percentage of respiratory specimens that tested positive for seasonal influenza viruses received by the CHP's Public Health Laboratory Services Branch peaked at 27.21 per cent in the week ending February 17 and declined to 5.97 per cent in the week ending March 31.

Meanwhile, the number of institutional influenza-like illness (ILI) outbreaks dropped from 115 cases (affecting 721 persons) in the week ending February 3 to four cases (13 persons) in the week ending March 31. As of yesterday (April 3) no ILI outbreaks had been recorded this week.

The weekly average rate of the ILI syndrome group in the accident and emergency departments decreased from the peak of 274.8 cases per 1 000 coded cases in the week ending February 17 to 168.5 in that ending March 31. In the same period, the overall admission rate in public hospitals with a principal diagnosis of influenza also decreased from the peak of 1.52 per 10 000 population to 0.17.

For adults, 570 cases of influenza-associated admission to the Intensive Care Unit or death (including 382 deaths) were recorded in this influenza season (from the week of January 7 to the week ending March 31). As for children (aged under 18), 20 severe cases (two deaths) were reported in the same period. Among the 20 cases, 19 (95 per cent) did not receive seasonal influenza vaccination for the current season.

As of April 2, about 475 300 and 332 800 doses of seasonal influenza vaccine (SIV) had been administered via the Government Vaccination Programme (free vaccination) and the Vaccination Subsidy Scheme (subsidised vaccination) respectively, increasing by 16 per cent and 17 per cent from the same period last year.

"Although the winter influenza season has ended, members of the public aged 6 months or above who have not yet received any SIV in the 2017/18 season can still receive it for personal protection against seasonal influenza. However, persons who have already completed seasonal influenza vaccination in the 2017/18 season are not recommended to receive any further dose of SIV within the same season.

"Meanwhile, the public should continue to adopt strict personal, hand and environmental hygiene practices against respiratory illnesses and other infectious diseases," the spokesman added.