Hong Kong is believed to be safe from the threat of A/H2N2 -- a flu strain that claimed millions of lives in the last century -- after authorities destroyed specimens of the deadly virus received from the US.

The move followed an urgent appeal by the World Health Organization (WHO) that laboratories should immediately destroy any specimen of the virus they had received from the College of American Pathologists (CAP).

H2N2 is highly contagious, and many people don't have immunity against it. It caused a worldwide pandemic from 1957 to 1958 that claimed 1 million to 4 million lives. The virus vanished in 1968 after the emergence of H3N2 that caused the next pandemic. Since then, H2N2 has been stored only in high-security biological laboratories, hence people born after 1968 have not developed natural immunity against it. What's more alarming is that the current trivalent influenza vaccines are not anti-H2N2.

A spokesman for the Centre for Health Protection (CHP) in the SAR said yesterday that the laboratory of Queen Mary Hospital was the only local institution that had the specimen. And after getting the WHO notification, the CHP immediately contacted the hospital, which said its laboratory had not worked on it after April 1.

The specimens were destroyed on Tuesday, the spokesman said. The laboratory technicians haven't reported any symptoms of the influenza since then and CHP's surveillance system hasn't received any reports of H2N2 cases in the SAR.

The countdown to the global alert began on March 26 when Canadian health authorities informed WHO that a local laboratory was startled to identify the virus similar to those found in humans in 1957 and 1958 at the beginning of the outbreak, now known as the Asian influenza pandemic.

A WHO statement issued yesterday said investigation by Canadian authorities traced the source to a panel of proficiency testing samples containing influenza A and B viruses that the Canadian laboratory got from the CAP in February.

It's routine for CAP to send various panels of proficiency testing samples to participating laboratories every year and normally, H3N2 and H1N1 viruses are used.

It was on April 8 that WHO informed the US health authorities of the situation. Further investigation, according to the WHO statement and "The Washington Post", showed that the problem arose when Meridian Bioscience, a private company in Cincinnati, sent the specimens to 3,747 laboratories for testing as part of CAP's quality-control certification. Sixty-one of the laboratories are in 16 countries and cities other than the US and Canada.

It was also found that more H2N2 samples were sent to another 2,750 laboratories in the US by other proficiency testing providers for other certification processes. On April 8 itself, at the request of the US Government, CAP called on all participating laboratories to immediately destroy the samples containing the deadly virus. On April 12 -- the day Hong Kong destroyed the specimens -- CAP again contacted the laboratories to confirm that they had been destroyed.

The WHO statement said there had been no reports of H2N2 infections among laboratory workers associated with the H2N2 samples.

(China Daily HK Edition April 14, 2005)