Influenza A virus subtype H2N2

H2N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus). H2N2 has mutated into various strains including the Asian Flu strain (now extinct in the wild), H3N2, and various strains found in birds. It is also suspected of causing a human pandemic in 1889.^[1][2]

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Asian flu

The "Asian Flu" was a category 2 flu pandemic outbreak of avian influenza that originated in China in early 1956 lasting until 1958. It originated from mutation in wild ducks combining with a pre-existing human strain.^[3] The virus was first identified in Guizhou.^[4] It spread to Singapore in February 1957, reached Hong Kong by April, and US by June. Death toll in the US was approximately 69,800.^[3] Estimates of worldwide infection rate varies widely depending on source, ranging from 1 million to 4 million.

Asian Flu was of the H2N2 strain (a notation that refers to the configuration of the hemagglutinin and neuraminidase proteins in the virus) of type A influenza, and a influenza vaccine was developed in 1957 to contain its outbreak.

The Asian Flu strain later evolved via antigenic shift into H3N2 which caused a milder pandemic from 1968 to 1969.^[5]

Both the H2N2 and H3N2 pandemic strains contained Avian influenza virus RNA segments. "While the pandemic human influenza viruses of 1957 (H2N2) and 1968 (H3N2) clearly arose through reassortment between human and avian viruses, the influenza virus causing the 'Spanish flu' in 1918 appears to be entirely derived from an avian source (Belshe 2005)." ^[6]

Test kits

From October 2004 to February 2005, some 3,700 test kits of the 1957 H2N2 virus were accidentally spread around the world from the College of American Pathologists (CAP). CAP assists laboratories in accuracy by providing unidentified samples of viruses; private contractor Meridian Bioscience in Cincinnati, U.S., chose the 1957 strand instead of one of the less deadly avian influenza virus subtypes. "CAP spokesman Dr. Jared Schwartz said Meridian knew what the virus was but believed it was safe. In selecting it, the company had determined that the virus was classified as a biosafety level 2 (BSL-2) agent, which meant it could legally be used in the kits. [...] Before the problem came to light, the CDC had made a recommendation that the H2N2 virus be reclassified as a BSL-3 agent, Gerberding said. She promised to speed up the reclassification. The CDC determines the classifications in collaboration with the National Institutes of Health. In BSL-3 labs, agents are handled with equipment designed to prevent any airborne contamination and resulting respiratory exposure."^[7] The 1957 H2N2 virus is considered deadly and the U.S. government called for the vials containing the strain to be destroyed.

"CDC officials reported on April 21 that 99% of the samples had already been destroyed. News reports on April 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."^[8]

"In the United States, there is no government regulation over the 1957 flu strain. In fact, federal officials at the CDC do not even know how many U.S. laboratories keep this deadly strain in their viral libraries."^[9]

Sources

Further reading

• Pandemic preparedness: lessons learnt from H2N2 and H9N2 candidate vaccines
• Interim CDC-NIH Recommendation for Raising the Biosafety Level for Laboratory Work Involving Noncontemporary Human Influenza Viruses
• New Scientist: Bird Flu
• Pandemic-causing 'Asian flu' accidentally released
• Persistence of Q strain of H2N2 influenza virus in avian species: antigenic, biological and genetic analysis of avian and human H2N2 viruses