Russia’s bird flu epidemic is subsiding and should disappear by late August, according to a World Health Organization official quoted by the Reuters news agency.

But Russian health officials were less optimistic, suggesting birds migrating from the five Siberian regions where the deadly virus has been raging since mid-July could spread the disease as far afield as the United States.

“Things are quieting down. The (epidemic) will vanish in 10-15 days,” Oleg Kiselyov, head of a research institute operating under the WHO’s auspices, told reporters St Petersburg. “It won’t spread further because of changing weather conditions. It’s never warm enough in Siberia in late August.”

The H5N1 strain, which has struck mainly in the western Siberian region of Novosibirsk, has killed over 50 people in Asia since 2003.

Outbreaks that have killed wildfowl and poultry in Russia and Kazakhstan since mid-July have raised fears the disease could spread to humans on the Eurasian land mass, sparking fears of a worldwide epidemic.

But Kiselyov said there was no need for such worries in Siberia. “If no one has been infected so far, people won’t get infected. All the measures undertaken have helped localize the outbreak.”

He added, however, that Russia would soon test and introduce a new type of vaccine to prevent humans from getting the potentially deadly virus. The first batch will be sent to the worst-hit Novosibirsk region as soon as October, he said.

The Emergencies Ministry said that the number of deaths among domestic and wild birds was just 15 overnight compared with a total of 5,583 since mid-July.

 But Russia’s top epidemiologist, Gennady Onishchenko, said it was too early to draw rosy conclusions.

“The (epidemic) is being localized. Its spread is currently limited to five regions, but that does not mean that birds could not be dying somewhere else,” he was quoted as saying by Interfax news agency in Novosibirsk.

“We would’ve been drinking champagne by now if it had been pinned down,” he added.

There were also fears among Russian veterinary officials that migrating birds could take the virus to other countries.

“It’s possible that they (birds) have already spread it (beyond Russia),” Yevgeny Nepoklonov, deputy head of the state veterinary watchdog, told Interfax.

“They (birds) fly not only over Siberia but also along the far eastern coast on to the United States of America. Some birds fly along the Kazakh border from Novosibirsk water reservoirs and then on to the (Volga town) of Volgograd.”

In Uzbekistan, the agriculture ministry said it was suspending imports of poultry and eggs from Russia and Kazakhstan due to the outbreak.

The move followed similar plans by the European Union, although the EU buys no poultry from the two ex-Soviet countries.