the need for any recommendation to balance both risks and benefits, the current uncertainty about the severity of influenza A (H1N1) illness, the readiness of vaccine seed strains and reagents for largescale vaccine production, the current status of production of seasonal vaccine for the Northern hemisphere, and the risks associated with a premature cessation of seasonal vaccine production, The Working Group considered it premature to recommend that commercialscale production of influenza A (H1N1) vaccine should start immediately.

The Working Group did make the following recommendations for immediate action:

The WHO Secretariat, in close coordination with its Collaborating Centers and the Essential Regulatory Laboratories of the WHO Global Influenza Surveillance Network, should recommend which vaccine viruses should be used for vaccine development as soon as possible Essential reagents to calibrate antigenic content should be made available as a priority The WHO Secretariat is encouraged to collaborate actively with its Collaborating Centres, Essential Regulatory Laboratories, and with industry, to assess the growth property of vaccine viruses and identify those with best growth potential, in order to maximize output of vaccine. Manufacturers are urged to develop clinical trial batches and accelerate initiation of clinical trials of influenza A (H1N1) vaccines and to start preparing for a potential future recommendation to move to commercialscale production. The above activities should not interfere with the present production of the Northern hemisphere seasonal vaccines The number of needed doses of A (H1N1) vaccine will depend on the spread of influenza A (H1N1) virus in the next few weeks and on a better definition of the groups to be targeted An evidencebased recommendation for the groups to be targeted for vaccination still requires more data

Finally, the Working Group stressed the fact that clear communications are needed from WHO that declaration of Phase 6 does not automatically mean that WHO is recommending that manufacturers should switch from seasonal to influenza A (H1N1) vaccine production. Likewise, it is important to be clear that a potential recommendation to start production is not considered as a recommendation to start immunizing large population groups.

The Working Group agreed to continue to monitor the evolving situation carefully and made a provisional plan to review the accumulated evidence in the next few weeks to consider whether to recommend initiation of commercialscale production of influenza A (H1N1) vaccine.

There will also clearly be longer term issues that will need consideration such as the impact of a switch from seasonal manufacturing on subsequent supplies of seasonal vaccine for the Southern hemisphere, the safety and immunogenicity of A (H1N1) vaccine candidates as well as recommendations on the use of A (H1N1) vaccines when they become available.

Having reviewed the report of the May 14 meeting of the Ad Hoc Advisory Working Group on Influenza A (H1N1) Vaccines, SAGE agrees with its conclusions and recommendations for communication to the Director General of WHO.

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