Public health experts have warned that an H5N1 vaccine deal Indonesia has struck with a pharmaceutical company may jeopardize the world's access to a pandemic vaccine, if the country becomes the epicenter of a global outbreak.

Indonesia on Wednesday signed a memorandum of understanding with U.S. drug manufacturer Baxter Healthcare Corp. to develop a human bird flu vaccine.

Under the agreement, Indonesia will provide H5N1 virus samples in exchange for Baxter's expertise in vaccine production. Other organizations would have access to Indonesian samples provided they agree not to use the viruses for "commercial" purposes, said Siti Fadilah Supari, Indonesia's health minister.

But that is a major departure from the World Health Organization's existing virus-sharing system, where bird flu viruses are freely shared with the global community for public health purposes, including vaccine and antiviral development. Indonesia has not shared any viruses since the beginning of 2007.

Indonesia defended its decision, arguing the system works against poor countries. "The specimens we send to WHO ... are then used by vaccine makers who then sell to us (at a profit)," Supari told reporters Wednesday. "This is unfair, we have the virus, we are getting sick, and then they take the virus from WHO -- 'with WHO's permission' they say -- and make it themselves," said Supari.

Other countries, including China, Thailand and Vietnam, have previously stalled on sharing viruses. Like Indonesia, they fear the vaccines and drugs produced from their viruses would ultimately be unaffordable for them, leaving their populations dangerously vulnerable -- while rich countries add to their stockpiles.

"We understand Indonesia's concerns and the reasons they're not sharing the viruses," said Dr. David Heymann, WHO's top flu official. "But these viruses should be a public good." WHO is attempting to address these concerns by promoting technology transfers to developing countries, which would strengthen their capacity to manufacture vaccine.

Indonesia announced two new human H5N1 cases on Wednesday. The U.S. Embassy in Jakarta also advised Americans to avoid contact with stray cats after confirmed reports of H5N1 infection in felines. Although cats have previously been infected with bird flu in Indonesia and other countries, there have been no known instances of cat-to-human transmission. As Indonesia is the country that has logged the most H5N1 activity this year, scientists are particularly keen to track the virus' evolution there.

Without samples of Indonesia's H5N1 viruses, scientists worldwide are at a big disadvantage in developing a possible pandemic vaccine. Indonesia continues to be the centre of most bird flu activity, and having access to recent viruses is essential to producing vaccines that match the dominant strains.

"There are issues of generosity on both sides here," said Dr. Alan Hay, director of the WHO Influenza Collaborating Centre at Britain's National Institute for Medical Research. "If a pandemic virus emerges in a place where we don't have access to viruses, it could really be quite disastrous," said Hay.

Indonesia said it stopped sharing viruses simply because the paperwork was not in place. Contracts known as material transfer agreements must be signed whenever research information, including viruses, is shared between two parties.

According to Triono Soendoro, director-general of Indonesia's National Institute for Health Research and Development, these agreements have not existed since 2005. "We were warned by national authorities not to send out viruses without these agreements, and now we are being blamed for not sharing," said Soendoro. WHO has yet to receive a proposed agreement, despite being in negotiations with Indonesia since November.

Indonesia has deposited the sequence data of its viruses into a publicly available database "for the good of the world," Soendoro said. Simply having genetic data, however, is no substitute for the actual viruses, which are needed for risk assessment purposes. "We need to be able to see that virus to see if it's stable or if it's mutating," said Heymann.

WHO's flu-sharing network, originally set up to share seasonal flu viruses for vaccine development, has in recent years been adapted to monitor H5N1 activities. For 50 years, countries have freely shared viruses.

"If the system changes, this will hurt us all," said Heymann. "It puts us at risk of not getting the right vaccine during a pandemic."