Although the risk for the general public is considered low, the United Nations health agency is calling on nearly 4,000 laboratories, mostly in the United States and Canada, to destroy immediately flu proficiency testing samples containing a sometimes deadly strain for which many people have at best limited immunity.
In addition to this precautionary measure, the World Health Organization (WHO) is also recommending that biosafety procedures be reviewed for use on influenza viruses that have not circulated recently in humans and against which the majority of the population would have no protective immunity. Sixty-one of the laboratories are scattered among 15 other countries.
The H2N2 viruses at issue, sent out in testing samples by the College of American Pathologists (CAP), is similar to H2N2 viruses that circulated in humans in 1957-1958 at the beginning of the so-called Asian influenza pandemic, which claimed scores of thousands of lives in some countries.
Though a vaccine was quickly developed, H2N2 continued to circulate in humans and cause annual epidemics until 1968, when it vanished after the emergence of A/H3N2 viruses that caused the next pandemic. Thus persons born after 1968 are expected to have no or only limited immunity to H2N2 which is not contained in current trivalent vaccines.
The current H2N2 was traced back from a Canadian laboratory to CAP, which routinely provides such panels of proficiency testing samples to participating laboratories every year. Normally, currently circulating influenza A viruses (H3N2; H1N1) are used. The H2N2 virus was sent out for the first time in October 2004.
Subsequent investigation revealed that similar proficiency testing samples with H2N2 virus were sent to 3,747 laboratories.
There have so far been no reports of H2N2 infections in laboratory workers. Proper use of biological safety cabinets, along with recommended personal protective equipment, greatly reduces the risk of laboratory-acquired influenza infections and only a few such infections have been documented in the past. The risk for the general population is also considered low.
Countries and areas where the samples were sent besides the United States and Canada are: Bermuda; Belgium; Brazil; Chile; France; Germany; Hong Kong Special Administrative Region of China; Israel; Italy; Japan; Lebanon; Mexico; Republic of Korea; Saudi Arabia; Singapore and Taiwan, Province of China.