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Latest update of surveillance data in winter influenza season

     The Centre for Health Protection (CHP) of the Department of Health today (March 11) 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.

     "Although the latest surveillance data show that local influenza activity continued to decrease, it is still elevated above the baseline. We expect that Hong Kong will remain in the winter influenza season in the coming few weeks. In addition, influenza B virus detections are on the rise and continued vigilance is warranted," a spokesman for the CHP said.

Laboratory surveillance

     The percentage positive for seasonal influenza viruses decreased from 22.3 per cent in the last week of February to 19.5 per cent last week, compared with 38.7 per cent (peak) in the last week of January and 15.4 per cent (arrival of season) in the first week of 2015 among respiratory specimens received by the CHP's Public Health Laboratory Services Branch.

     Of note, the proportion of A(H3N2) dropped from 92.2 per cent to 86.4 per cent in the last two weeks while that of B correspondingly increased from 6.5 per cent to 10.5 per cent among influenza virus detections. That of A(H1) and C remained low.

     "The proportion of B is on the rise. Virus characterisation studies to date show that most detections belong to the Yamagata lineage and very few from the Victoria lineage. Characterisation so far does not reveal significant differences from the vaccine virus strains, B/Massachusetts/2/2012-like virus (Yamagata) in trivalent influenza vaccine (TIV) as well as quadrivalent influenza vaccine (QIV); and B/Brisbane/60/2008-like virus (Victoria) in QIV, recommended by the World Health Organization for the 2014/15 winter season for the northern hemisphere," the spokesman said.

     "Hence, while TIV of the current season may potentially prevent the majority of influenza B locally so far, QIV may potentially offer additional protection against strains of Victoria lineage, as recommended by the Scientific Committee on Vaccine Preventable Diseases last August. Citizens yet to be vaccinated should do so promptly as it can reduce disease severity, hospitalisations and deaths, particularly for high-risk groups," the spokesman added.

     As of March 8, about 253 000 doses and 244 000 doses of influenza vaccines had been administered to eligible groups under the Government Vaccination Programme and the Vaccination Subsidy Schemes 2014/15 respectively, an eight per cent and four per cent increase from the same period of last year.

Severe cases and institutional outbreaks

     From noon yesterday (March 10) to noon today, two additional cases of influenza-associated admission to intensive care units or death (including two deaths) among adults aged 18 or above had been recorded under the enhanced surveillance in collaboration with public and private hospitals reactivated since January 2, bringing the total to 482 (361 deaths) so far. Among them, 459 were A(H3N2), five were A(H1N1)pdm09, seven were A pending subtype and 11 were B. In the last winter season in early 2014, 266 cases (133 deaths) were filed.

     Last week (from March 1 to 7), 57 cases (44 deaths) were recorded. Separately, a daily average of 6.1 cases (5.1 deaths) were filed in the last seven days (from March 4 to 10), compared with 8.1 cases (5.7 deaths) in the preceding seven days (from February 25 to March 3).

     Meanwhile, an additional case of severe paediatric influenza-associated complication or death among children aged under 18 has been reported since yesterday via the ongoing reporting system, bringing the total this year to 18 (one death) and all were A(H3N2). In 2014, 27 cases (four deaths) were filed.

     Turning to influenza-like illness (ILI), four institutional outbreaks (affecting 19 persons) were reported to the CHP yesterday (March 10) by residential care homes for the elderly (two outbreaks, eight persons) and schools (two outbreaks, 11 persons).

     The weekly number decreased from 26 (affecting 121 persons) in the last week of February to 11 (55 persons) last week when most schools resumed after the Lunar New Year. As of yesterday, seven (36 persons) had been recorded so far this week. Outbreaks in the past four weeks mainly occurred in residential care homes for the elderly (66.0 per cent).

Situation of neighbouring and overseas areas

     The influenza activity of a number of overseas areas in the northern hemisphere has peaked and has been decreasing while that of the others remained elevated, with A(H3N2) virus predominating so far.

     The influenza season in Taiwan persisted as the percentage positive for influenza viruses stood at a high level of 29.9 per cent in the second and third weeks of February. That in Europe remained at a high level of 50 per cent in the week ending March 1, which is over the threshold of 10 per cent.

     In Japan, the average number of reported ILI cases per sentinel site has been decreasing. The percentage positive for influenza viruses in the United States, Canada and England has also been decreasing.

     The public should maintain good personal and environmental hygiene against influenza and other respiratory illnesses:

* Receive seasonal influenza vaccination for personal protection;
* Wash hands with liquid soap and water properly whenever possibly contaminated;
* When hands are not visibly soiled, clean them with 70 to 80 per cent alcohol-based handrub;
* Wash or clean hands frequently, especially before touching the mouth, nose or eyes, or after touching public installations such as handrails or door knobs;
* Cover the nose and mouth when sneezing or coughing, and wash hands thoroughly afterwards;
* Dispose of soiled tissue paper properly in a lidded rubbish bin;
* Put on a surgical mask when respiratory symptoms develop;
* Maintain good indoor ventilation;
* When influenza is prevalent, avoid going to crowded or poorly ventilated public places; high-risk individuals may consider putting on surgical masks when staying in such places; and
* Maintain a balanced diet, exercise regularly, take adequate rest, do not smoke and avoid overstress.

     The public may visit the CHP's pages below for more information:

* The influenza page (;
* The weekly Flu Express report (;
* The update on severe seasonal influenza cases (;
* The vaccination schemes page (;
* The list of participating doctors (;
* The Facebook Page (; and
* The YouTube Channel (

Ends/Wednesday, March 11, 2015
Issued at HKT 17:31


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