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Science, Energy & Environment

Single-Dose Vaccines for Pandemic H1N1 Will Protect Most Adults

15 September 2009

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Washington -- Pandemic H1N1 influenza continues its sweep through nations in the Northern Hemisphere and Southern Hemisphere as national health officials and vaccine manufacturers in several countries work to begin producing the first doses of vaccine to protect people against the novel flu.

Most patients continue to experience only mild illness, and viruses from all outbreaks remain virtually identical. The genetic stability of the H1N1 virus so far means that vaccines now in development, testing and production will match the circulating virus and give those who are vaccinated protection from the pandemic flu. But influenza is a rapidly mutating virus, and there is no guarantee that it will remain stable indefinitely.

The World Health Organization (WHO) reports more than 277,607 laboratory-confirmed cases and at least 3,205 deaths as of September 6, an increase of more than 23,401 cases and at least 368 deaths since August 30. Because countries no longer test and report individual cases and only test people with severe illness, there are many more cases than the WHO numbers indicate.

According to the WHO Global Influenza Surveillance Network of 128 institutions from 99 countries, pandemic H1N1 continues to be the dominant virus in circulation. In the United States, where the flu season has begun, 98 percent of viruses identified between August 30 and September 5 were pandemic H1N1, according to the Centers for Disease Control and Prevention (CDC).

Since 1968 the dominant circulating virus has been H3N2, but since 1977 an H1N1 virus circulated along with it, author John Barry wrote in a July 27 paper on novel H1N1 prepared for the Massachusetts Institute of Technology’s Center for Engineering Systems Fundamentals. Vaccines now being developed against seasonal flu are designed to protect against H3N2, the older H1N1 and another kind of flu called influenza B.

Pandemic H1N1 and the older H1N1 have little in common -- the novel H1N1 is called a "triple reassortant" swine flu virus, meaning its eight genes come from a combination of avian, human and swine flu viruses in different parts of the world.

"While the individual genes have all been seen before in other influenza viruses," Barry wrote, "the present combination has not been seen."

Around the World

On September 11, WHO reported that flu activity continues to decline in Chile, Argentina, Australia, New Zealand, South Africa and other temperate regions of the Southern Hemisphere. Many countries in Central America and the Caribbean also reported declining activity for the second week in a row.

H1N1 transmission persisted in tropical regions of the Americas and Asia, according to WHO, and Bolivia, Ecuador, Venezuela and other countries in the tropical region of South America reported rising cases of respiratory disease. Respiratory disease was regional or widespread in the tropical regions of Asia and increasing in India, Bangladesh and Cambodia.

In the United States, the 2009–2010 flu season officially begins October 4, but during a September 11 briefing, Dr. Anne Schuchat, director of CDC’s National Center for Immunization and Respiratory Diseases, said, "The flu season has started. The 2009 H1N1 virus never went away this summer and right now what we’re seeing is an increase of influenza-like activity around the country."

As of September 6, WHO reported on pandemic H1N1 cases and deaths in each of its regions -- Americas (120,653 cases with 2,467 deaths), Eastern Mediterranean (9,844 cases, 51 deaths), Europe (more than 49,000 cases, at least 125 deaths), Southeast Asia (22,387 cases, 221 deaths), and Western Pacific (69,387 cases, 306 deaths). As of September 10, 24 African countries had officially reported 8,125 laboratory-confirmed cases, including 40 deaths.

Pandemic Vaccine

Despite concerns in the early days of the novel H1N1 pandemic that people would need two doses of a vaccine for pandemic protection or a vaccine plus an adjuvant (supplement) to increase the immune system’s response, clinical studies in China and the United States show that one dose may protect healthy people from the new flu.

Chinese health officials have given Sinovac, a Chinese biotechnology company, approval to produce a single-dose H1N1 vaccine, according to news reports, and the nation’s Food and Drug Administration is considering H1N1 manufacturing applications from nine other drug firms. The Chinese Ministry of Health reports more than 9,000 confirmed cases of H1N1 on the mainland.

On September 11, Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health (NIH), announced that NIH-sponsored clinical trials confirm test results from manufacturing companies Sanofi Pasteur and CSL Limited indicating that a single dose of pandemic H1N1 vaccine produces a robust immune response within eight to 10 days in most healthy adults.

"This is very good news for the vaccination program," Fauci said, "both with regard to the supply of vaccine as well as to its potential efficacy."

On August 17, WHO, the International Federation of Red Cross and Red Crescent Societies, U.N. humanitarian organizations and the U.N. System Influenza Coordinator announced a plan to work with partners in nongovernmental organizations and civil societies to support governments and communities to reduce the pandemic’s impact.

This includes countries where health services are overburdened by diseases like HIV/AIDS and tuberculosis and that will have difficulty managing a surge of H1N1 cases.

More information about pandemic H1N1 is available at these Web sites: CDC, WHO and


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