Launch of WHO H5N1 vaccine stockpile still awaited

May 16, 2008 (CIDRAP News) – A year after the World Health Organization (WHO) called for the development of an international stockpile of vaccines against H5N1 influenza, the stockpile has not yet materialized, the WHO said in a report released today.

At the World Health Assembly in May 2007, WHO member countries called on the WHO leadership to set up an international vaccine stockpile against H5N1 and other influenza viruses of pandemic potential. And in June, the pharmaceutical company GlaxoSmithKline (GSK) pledged to donate 50 million doses of vaccine to the stockpile over 3 years.

In today's report, the WHO says development of a stockpile is under way, but no doses have been acquired yet.

"At this time, a physical WHO stockpile of H5N1 vaccine does not exist, and its development will depend on several factors, including discussions with manufacturers on the terms and conditions of their donation, as well as on technical issues such as obtaining further information on the stability of vaccines," says the report, which is based on a scientific meeting held in Geneva in October 2007.

The 26-page report assesses the development of H5N1 vaccines to date and discusses their possible uses, including how the planned WHO stockpile would be used. The document is titled "Options for the Use of Human H5N1 Influenza Vaccines and the WHO H5N1 Vaccine Stockpile."

In 3 more years, the report says, the stockpile could contain 50 million doses, or enough to vaccinate 25 million people with two doses each, which is likely to be needed to generate a good immune response.

The WHO says the contemplated uses of the stockpile are (1) to help contain the initial, localized emergence of a potential H5N1 pandemic if the event is identified early enough and (2) to supply vaccine to countries that otherwise would have little access to it once sustained human-to-human transmission is under way.

For several reasons, vaccination alone would probably not be enough to contain a local outbreak of an emerging pandemic virus, the report says. However, "mathematical modeling approaches suggest that under certain conditions, vaccination could make a significant addition to the effects of other control actions."

Concerning the eventual size of the stockpile, the WHO states, "Based on the results of the consultation described in this report, a stockpile of approximately 100 million doses may be warranted given its potential uses."

In addition to GSK, companies that have expressed a willingness to contribute to the stockpile include Omninvest of Hungary, Baxter, and Sanofi Pasteur, the document says.

The report says that at least 16 companies have H5N1 vaccines in "relatively advanced development." Studies on the vaccines so far suggest that they should be safe and effective, but their effectiveness can be confirmed only by trials in which people are exposed to H5N1 either experimentally or in an outbreak, the WHO states.

The document notes that H5N1 vaccines generally elicit lower immune responses than seasonal flu vaccines do, but adjuvants boost the response.

Results to date also suggest that H5N1 vaccines may protect people against strains other than the one used in the vaccine, the report says. "Animal data suggest that vaccination by human H5N1 influenza vaccines, produced from viruses of one clade, may confer cross-reactivity against H5N1 viruses from other clades and therefore may confer protection against challenge by H5N1 viruses from other clades."

In addition, this cross-reactivity "might indicate potential cross-protection against future emerging strains, but such coverage could diminish as H5N1 vaccines continue to evolve."

See also:

Full text of WHO report
http://www.who.int/csr/resources/publications/WHO_HSE_EPR_GIP_2008_1d.pdf

Jun 13, 2007, CIDRAP News story "Glaxo to give 50 million doses of H5N1 vaccine to WHO"

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