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No significant antigenic changes detected in local circulating H3 strain
     In response to press enquiries on the latest recommendations on seasonal influenza vaccination (SIV) of the World Health Organization (WHO), the Centre for Health Protection (CHP) of the Department of Health today (October 3) pointed out that no significant antigenic changes had so far been detected in the local circulating influenza A(H3) virus strain.

     The WHO regularly reviews the global epidemiology of influenza twice every year to recommend virus strains for inclusion in SIV for use in the northern hemisphere (NH) and southern hemisphere (SH) respectively in accordance with the available data. In general, it takes six to eight months for the production and approval of vaccines. In February 2017, the WHO recommended the composition of SIV to be used in NH including Hong Kong in the 2017/18 season.

     The CHP noted that the WHO on September 28 (Melbourne time) released its recommended trivalent influenza vaccine (TIV) strains for the 2018 SH influenza season, including:
  • An A/Michigan/45/2015 (H1N1) pdm09-like virus;
  • An A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus; and
  • A B/Phuket/3073/2013-like virus.

     The quadrivalent influenza vaccine (QIV) should contain the above trio and a B/Brisbane/60/2008-like virus.

     "Regarding the H3N2 strain, we noted that the WHO recommended an A/Hong Kong/4801/2014 (H3N2)-like virus for NH while the above Singapore strain for SH. Both are antigenically similar with no antigenic drift," a spokesman for the CHP said.

     In fact, in the past three years, after releasing recommendations for the NH SIV strains, the WHO made different recommendations for the SH SIV strains in the same year. Apart from the winter influenza season in 2014/15, no antigenic drift was detected in other seasons.

     According to the WHO's report, influenza A(H3N2) and B viruses were predominant globally from February to September 2017. Studies showed that recent H3N2 viruses had been better inhibited by a ferret antiserum raised against the above egg-propagated Singapore strain, compared to other egg-propagated viruses (including the above Hong Kong strain). The Singapore strain was hence recommended as the vaccine strain.

     "Our virus characterisation has so far detected no significant antigenic changes in the currently circulating H3 strain. Members of our Scientific Committee on Vaccine Preventable Diseases and its Working Group on Influenza Vaccination have been informed of the WHO's report. We will continue to closely monitor the local and global influenza activities, predominating strains, vaccine effectiveness and relevant scientific literature," the spokesman said.

     Locally, SIV programmes 2017/18 will be launched this month and the TIV strains include: the above Michigan H1N1, Hong Kong H3N2 and the above Brisbane influenza B strain. The QIV should contain the above trio and the above Phuket influenza B strain. The NH vaccine can provide protection against the above strains.

     "The latest surveillance data show that the local influenza activity remained at a low level and the positive percentage of seasonal influenza viruses was 2.79 per cent in the week of September 17. As the winter influenza season is yet to arrive, epidemiological and virological data as well as scientific evidence are still insufficient to forecast the possible predominating strains in the coming winter influenza season and it is too early at this stage to predict whether the NH vaccine strains match with the future circulating viruses, the vaccine effectiveness and if SH vaccines should be considered," the spokesman said.

     The CHP highlighted that when vaccine strains closely match with circulating viruses, the vaccine efficacy typically ranges from 70 to 90 per cent. In addition, vaccination will provide a certain degree of cross-protection even for different but related strains and will reduce disease severity particularly for high-risk groups including children, the elderly and chronic patients. Vaccination and strict personal and environmental hygiene remain the best means to prevent influenza.
Ends/Tuesday, October 3, 2017
Issued at HKT 19:50
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