Persons born after 1968 are expected to have no or only limited immunity to H2N2. H2N2 virus is not contained in current trivalent influenza vaccines.

The full text of the April 12 WHO statement on the H2N2 crisis follows:

The Public Health Agency of Canada (PHAC) informed WHO on 26 March that an influenza A/H2N2 virus was identified by a local laboratory in Canada. The H2N2 virus identified was found to be similar to H2N2 viruses that circulated in humans in 1957-58 at the beginning of the so-called Asian influenza pandemic.

The H2N2 virus which circulated at this time was fully transmissible among humans. It continued to circulate in humans and cause annual epidemics until 1968, when it vanished after the emergence of influenza A/H3N2 viruses that caused the next pandemic. Therefore, persons born after 1968 are expected to have no or only limited immunity to H2N2. H2N2 virus is not contained in current trivalent influenza vaccines.

Appropriate biosafety measures were immediately taken at the involved laboratory in Canada and respiratory surveillance measures initiated. Subsequent investigation by the Public Health Agency of Canada traced the source of the H2N2 virus to a panel of proficiency testing samples containing influenza A and influenza B viruses which the Canadian laboratory received from the College of American Pathologists (CAP) in February 2005.

Immediately Destroy Samples

CAP routinely sends various panels of proficiency testing samples to participating laboratories every year. Normally, currently circulating influenza A viruses (H3N2; H1N1) are used for proficiency testing. The H2N2 virus was distributed by CAP for the first time in October 2004.

WHO, the Department of Health and Human Services (HHS) in the USA and its Centers for Disease Control were informed of the situation by PHAC on 8 April.

Subsequent investigation revealed that similar proficiency testing samples with H2N2 virus were sent to 3747 laboratories in 18 countries. Sixty one of these laboratories are located in 16 countries outside the USA and Canada (see list of countries and areas below). HHS has recently learnt that other proficiency testing providers have sent additional H2N2 containing samples to further laboratories in the USA. HHS is taking steps to ensure the rapid destruction of this material.

On 8 April, after a request by the US government, CAP asked all laboratories which participated in the proficiency testing to immediately destroy samples containing the H2N2 virus.

On 12 April, a second correspondence from CAP to these laboratories further requested that destruction of the H2N2 virus be confirmed and that any case of respiratory disease among laboratory workers be investigated and notified to national authorities. WHO has received the list of addresses of the involved laboratories and has provided detailed contact information to the relevant Ministries of Health and requested their collaboration.

As of today, there have been no reports of H2N2 infections in laboratory workers associated with the distribution of the H2N2 samples from CAP.

Risk for General Population Is Considered Low

The proper use of biological safety cabinets, along with the use of recommended personal protective equipment, greatly reduces the risk of laboratory-acquired influenza infections. While a few H2N2 laboratory acquired infections have been documented in the past, the likelihood of laboratory-acquired influenza infection is considered low when proper biosafety precautions are followed.

The risk for the general population is also considered low. As a precautionary measure, WHO is recommending that all samples of the proficiency testing panel from CAP and any other proficiency testing providers containing H2N2 and any derivates be destroyed immediately.

WHO further recommends 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.

List of countries and areas

Bermuda
Belgium
Brazil
Chile
France
Germany
Hong Kong Special Administrative Region of China
Israel
Italy
Japan
Lebanon
Mexico
The Republic of Korea
Saudi Arabia
Singapore
Taiwan, China