All H2N2 flu virus samples destroyed, CDC says

May 3, 2005 (CIDRAP News) – All samples of a potentially dangerous influenza virus that were sent to thousands of laboratories in 18 countries in recent months have been accounted for and destroyed, federal health officials announced today.

Samples of the influenza A(H2N2) virus, which caused the flu pandemic of 1957-58, were sent to more than 6,000 labs for use in testing the labs´ ability to identify flu viruses. Most of the labs were in the United States.

The Centers for Disease Control and Prevention (CDC) said the organizations that administer proficiency testing reported that all the samples had been destroyed. No reports of illness have been linked with possible exposure to the samples, the CDC said. The virus has not circulated since 1968, which means that most people now would have little or no immunity to it.

"Certification of the destruction of the H2N2 samples contained in the proficiency testing kits effectively ends the immediate risk associated with distribution of these kits, but it is only the first step of the public health response," the CDC said. A multiagency task force will investigate what caused the inclusion of H2N2 in the test kits, the statement added.

Also today, the CDC and the National Institutes of Health (NIH) recommended that labs use stricter safety precautions when handling H2N2 virus samples. The agencies released a recommendation that labs use Biosafety Level 3 (BSL-3) instead of BSL-2 precautions when working with the virus. A similar recommendation was made for highly pathogenic avian influenza (HPAI) viruses and for reverse-genetics research on the 1918 pandemic flu virus.

Starting last fall, samples of the H2N2 virus were sent to labs in 18 countries for routine testing that usually involves more benign flu strains. Meridian Bioscience Inc. of Cleveland sent the kits on behalf of the College of American Pathologists (CAP) and three other US organizations that administer lab proficiency testing. Why the H2N2 virus was used has not been fully explained. But the virus was classified as BSL-2 at the time, which meant it could legally be used in the kits, CAP officials have said.

In the testing, labs have to determine if a virus is influenza and whether it is type A or B, without identifying the subtype. But Canadian government researchers discovered in March that the virus they had been sent was H2N2, which led the World Health Organization on Apr 12 to urge labs to destroy all the samples. Most laboratories quickly did so, but a few samples were missing, which triggered an urgent search.

CDC officials reported on Apr 21 that 99% of the samples had already been destroyed. News reports on Apr 25 said the last samples outside the United States had been destroyed at the American University of Beirut in Lebanon, after they were found at the Beirut airport.

Earlier reports said H2N2 samples were sent to 3,747 labs under CAP auspices and to about another 2,700 labs certified by other organizations. All but about 75 labs that received the CAP samples were in the United States, reports said. How many of the other labs were in the United States has not been made clear.

The biosafety recommendations released today are part of a new edition of guidelines for biomedical labs that will be published in full this fall, the CDC said. In BSL-3 labs, agents are handled with equipment designed to prevent any airborne contamination and resulting respiratory exposure for lab workers and others.

With regard to the 1918 pandemic virus, the recommendations state, "Any research involving reverse genetics of the 1918 influenza strain should proceed with extreme caution. The risk to laboratory workers is unknown at the present time but the pandemic potential is thought to be significant."

In recent studies, researchers have engineered viruses similar to the 1918 pandemic strain, H1N1, and exposed mice to them in an effort to learn what made the virus so deadly. The 1918 pandemic is estimated to have killed between 50 million and 100 million people around the world.

See also:

CDC update on H2N2 virus situation
http://www.cdc.gov/flu/han050305.htm

CDC´s interim safety recommendations for laboratories working with H2N2 and certain other influenza viruses
http://www.cdc.gov/flu/h2n2bsl3.htm

Nov 24, 2004, CIDRAP News story, "Recreated gene sheds light on lethality of 1918 flu virus"