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WHO Document Guides Strategic Use of H5N1 Vaccine and Vaccine Stockpile

By Kunal Rambhia, May 23, 2008

On May 16, 2008, the World Health Organization (WHO) released a document that discusses options for human use of H5N1 influenza vaccine as well as options for use of the WHO H5N1 vaccine stockpile. The report was produced following a WHO scientific consultation meeting that was held in October 2007. Although “a physical WHO stockpile of H5N1 vaccine does not exist,” in July of 2007, GlaxoSmithKline (GSK) announced it would deliver 50 million doses (which, assuming 2 doses per person, may be enough to vaccinate 25 million people) over 3 years “to support the WHO stockpile initiative.”

With regard to safety of human H5N1 vaccines, the WHO document notes that although “no major or unanticipated safety concerns have been identified related to the use of H5N1 influenza vaccines in humans,…significantly more safety data are needed.” Specifically, the WHO notes that more research is needed in: “controlled trials (especially in children and long-term follow-up studies” regarding the safety of adjuvanted and whole virus vaccines, and assessments of public perceptions of the risks/benefits of the H5N1 vaccine. Regarding the potential efficacy of human H5N1 vaccines, the WHO notes that although there have been no human trials that measure how protective H5N1 vaccines will be, initial studies on the human immune response to the H5N1 vaccine have indicated that use of an adjuvant in an H5N1 vaccine can increase a vaccine’s immune response, decrease the dosage required, and provide protection across clades of the virus.The WHO document also considered “five possible general options for using human H5N1 influenza vaccine” both before and during a pandemic:

Non-pandemic use

• To protect people at high risk of contracting zoonotic avian H5N1 influenza
• To “prime” the immune systems of people in selected groups or populations in anticipation of a possible H5N1 influenza pandemic; and
• To fully immunize people in selected groups or populations in anticipation of a possible H5N1 influenza pandemic.¹

Imminent pandemic or during pandemic use

• To help contain the initial and localized emergence of a potential H5N1 influenza pandemic; and
• To immunize people in selected groups or populations following sustained human-to-human transmission of an H5N1 influenza virus.¹

With regard to these five scenarios, the scientific advisory body concluded “that all of the options involve complex scientific, ethical and political considerations” Moreover, they noted that “for many options, the existing scientific evidence and considerations provide little support on which to base decision-making, but for certain options mathematical modelling [sic] may provide valuable insights.”

The WHO document also considers “preferred options” for use of the WHO H5N1 vaccine stockpile.  The expert group considered that the “two most feasible uses of this stockpile at the present time were considered to be:

• to help contain the initial and localized emergence of a potential H5N1 influenza pandemic if such an event is identified early enough; and
• to provide countries that are least able to obtain H5N1 vaccines with some level of supplies if sustained human-to-human transmission of an H5N1 influenza virus starts.”

The WHO concludes that the options for using H5N1 vaccine that are outlined in the document are heavily dependent on the properties and availability of vaccine. To date “at least 16 different manufacturers have an H5N1 vaccine in relatively advanced development,” each using a variety of methods, “including egg and cell culture grown viruses, live virus and inactivated virus vaccines, whole and split antigen, and vaccines with and without different adjuvants.”¹ The type and supply of vaccines will continue to influence the strategies that the WHO has offered.

References

1. Options for the use of human H5N1 influenza vaccines and the WHO H5N1 vaccine stockpile. World Health Organization. May 16, 2008. http://www.who.int/csr/resources/publications/WHO_HSE_EPR_GIP_2008_1d.pdf. Accessed May 23, 2008.