Current vaccines against the H5N1 avian influenza virus may protect against some future, genetically evolved strains of the virus, scientists reported Wednesday — additional fuel for the debate about whether to stockpile H5N1 vaccine or prime people’s immune systems before a pandemic. One country has already decided to take the leap. Switzerland announced Wednesday it will stockpile enough H5N1 vaccine to give each of its citizens a first priming dose of vaccine quickly, should an H5N1 pandemic occur. The vaccine will be made in Canada by GlaxoSmithKline. At the World Vaccine Congress in Vienna, flu vaccine giant Sanofi Pasteur announced that an H5N1 vaccine it made using a virus from Vietnam in 2004 triggered production of antibodies that can neutralize the H5N1 virus that caused an outbreak in Turkey in January of this year. It provides hope — but not proof — that the older vaccine might protect people who received it against strains related to the Turkish virus and even future strains. The viruses from Vietnam and Turkey belong to different subgroups or clades of H5N1 and it was not a given that a vaccine made with one would protect against the other. Agnes Hoffenbach, Sanofi’s head of influenza research and development, suggested the findings are promising but preliminary, and don’t guarantee the current vaccine would protect widely against future strains. “I think it’s encouraging data,'’ Hoffenbach said from Vienna. “But . . . if the circulating virus is even more divergent at some point maybe it would not be possible to neutralize it. But we don’t know yet.'’ In fact, Sanofi already has evidence the cross-protection probably doesn’t occur across the board with H5N1 viruses. It also tested to see if the antibodies produced by the vaccine would neutralize a virus like those now circulating in Indonesia — the current hot spot for H5N1 infection. The Indonesian and Turkish viruses belong to the same clade, though within that family they are cousins, not siblings. The antibody response to the Indonesian virus was poor, Hoffenbach acknowledged: “It’s not universally (cross-reactive) against all the strains from clade 2. Clade 2 is very vast.'’ Still, the idea that some vaccines could be useful against evolved strains of a possible pandemic virus is intriguing for those struggling to find ways to stretch limited vaccine production capacity to protect as many people as possible. It follows on the heels of last week’s release of a small but exciting U.S. study where people immunized with a vaccine made with a 1997 H5N1 virus showed a strong immune response when they were boosted last year with the 2004 Vietnam vaccine. Taken together, these and other findings suggest that it may not be necessary to vaccinate with the specific pandemic strain to protect people, some experts say. “There is accumulating scientific evidence that . . . there is cross reactivity, immunologically, and hopefully that will spell out cross protection,'’ said Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases. “This has some cause for cautious optimism that it’s not going to be a situation where you’re going to have to get a completely new vaccine each time if it (the virus) evolves a little,'’ he said. But Dr. Iain Stephenson, a British researcher who has done several H5N1 vaccine trials, was dubious, noting that with human flu strains, vaccine and virus have to be well matched for protection to be induced. “Vaccine strains are pretty strain specific and they don’t really cover mismatched strains.'’ Dr. Klaus Stohr, the World Health Organization’s special adviser for pandemic vaccine development, said the Sanofi findings will help countries trying to decide whether to stockpile vaccine or pre-prime their citizens. Canada currently doesn’t intend to pursue these options, saying there is too little science to support either. Stohr, who was enthusiastic about the Sanofi findings, agreed it’s still not clear how they would translate in the face of a pandemic challenge. “What it means in terms of the level of protection is hard to say. But definitely if there is virus neutralization there will be a benefit, . . . a clinical benefit.'’ In the event of a pandemic, even a little protection would be better than none, Stohr said. But as there is no way of knowing if a certain vaccine will protect against a particular future strain, stockpiling or using a system of advance vaccination — pre-priming — remains a crap shoot. “This is the gambling that is being done,'’ Stohr agreed. “But without any doubt there is some protection. With some (viruses) it’s better, others it’s not so good.'’ By HELEN BRANSWELL