Feb 14, 2005 (CIDRAP News) – The World Health Organization (WHO) has recommended adding a new influenza strain that emerged recently in California to the flu vaccine for 2005-06 in the Northern Hemisphere.
The new strain is called A/California/7/2004(H3N2), the WHO announced last week. The virus was first isolated from a flu patient in Santa Clara County last September, according to the Associated Press (AP). The Centers for Disease Control and Prevention (CDC) identified the strain as a new one in January, the AP reported.
The CDC's Feb 5 flu update says that 49 of 256 (19.1%) flu virus isolates that the agency has analyzed antigenically since October 2004 were most closely related to the new strain.
The flu vaccine normally contains three viral strains. The other two strains the WHO recommended for next season are the same as in this year's vaccine: A/New Caledonia/20/99(H1N1) and B/Shanghai/361/2002.
The United States usually follows the WHO recommendations. The third strain in this year's US vaccine is A/Fujian/411/2002(H3N2) or the antigenically equivalent A/Wyoming/3/2003(H3N2). The California strain is thought to be a variant of the Fujian strain, according to the AP report.
Klaus Stohr, head of the WHO's global influenza program, said new strains are recommended for the vaccine only when significant changes occur, according to a New York Times report. "A/California is profoundly different from what has been circulating before," Stohr told the Times.
Analysis of more than 10,000 viruses from 80 countries led to the recommendation for next season's vaccine, the WHO said. The WHO and its collaborating laboratories conducted the analyses.
The strains to include in each season's vaccine must be chosen early in the year because it takes roughly 6 months to produce the vaccine. The viruses used in vaccines are grown in chicken eggs.
The WHO said flu vaccine coverage has improved in the last 10 years but not enough to include everyone in high-risk groups. As defined by the WHO, those groups include the elderly, those who have other respiratory or cardiovascular disease that increases their risk of complications, and healthcare workers.
Last year the WHO set a goal of 60% coverage for people in high-risk groups, the agency said. It said flu vaccine use in developing countries remains "minimal to nonexistent."
Feb 10 WHO statement
CDC's weekly flu update
CDC information on this year's vaccine composition