CHICAGO/LONDON, May 27 (Reuters) - The United States and

Europe are taking steps to acquire or manufacture H5N1 bird flu

vaccines that could be used to protect at-risk poultry and dairy

workers, veterinarians and lab technicians, government officials

said, moves influenza experts say could curb the threat of a

pandemic.

U.S officials last week said they were moving bulk vaccine

from CSL Seqirus that closely matches the current virus

into finished shots that could provide 4.8 million doses of

vaccine. European health officials told Reuters they were in

talks to acquire CSL's prepandemic vaccine.

Canadian health officials said they have met with GSK

, maker of Canada's seasonal flu shots, to discuss

acquiring and manufacturing a prepandemic bird flu vaccine once

its seasonal flu production capacity is freed up.

Other countries, including the UK, are discussing how to

proceed on prepandemic vaccines, scientists said.

The actions follow the explosive spread of a new strain of

bird flu that emerged in late 2020 and has caused unprecedented

numbers of deaths among wild birds and domestic poultry and has

begun infecting many mammal species.

In March, U.S. officials reported the first outbreak of the

virus in dairy cattle, which has infected dozens of herds in

nine states and two dairy workers. The U.S. Food and Drug

Administration has estimated that 20% of the U.S. milk supply

shows signs of the virus, indicating a wider spread is likely.

Human exposures to the virus in poultry and dairy operations

could increase the risk that the virus will mutate and gain the

ability to spread easily in people.

"All of our efforts need to be focused on preventing those

events from happening," said Matthew Miller, co-director of the

Canadian Pandemic Preparedness Hub at McMaster University. "Once

we have widespread infections of humans, we're in big trouble."

Dr. Angela Rasmussen, a virologist at the University of

Saskatchewan, said she has been in discussions with U.S. and

Canadian officials about using vaccines to protect workers

following the virus' spread into new mammal species.

Dawn O'Connell of the U.S. Administration for Strategic

Preparedness and Response said the government is "looking

closely" at the possibility of vaccinating farm workers and

others in close contact with the virus.

The U.S. has contracts with CSL and GSK to test prepandemic

vaccines that more closely match the circulating virus than

older H5N1 vaccines in the stockpile. The U.S. is moving forward

with the CSL vaccine, a Department of Health and Human Services

official confirmed.

Discussions about prepandemic vaccine use are going on at

government levels and among scientists in a number of places,

including in the UK, said Wendy Barclay, chair in influenza

virology at University College London, who also researches avian

flu for the UK Health Security Agency.

If deployed strategically to dairy farmers, healthcare

workers and those in close contact with infected animals, "it

would put a pin in the virus," she said, although she said it

was not clear if this step was necessary yet.

The UK government did not comment but said it is monitoring

the situation in the U.S.

In Europe, the European Commission's Health Emergency

Preparedness and Response Authority is working on a joint

procurement of CSL Seqirus's vaccine to "potentially prevent a

pandemic" sparked by individuals exposed to infected birds and

animals, spokesman Stefan De Keersmaecker told Reuters.

A spokeswoman for CSL, which has contracts for pandemic

influenza vaccines with 30 governments, said the company has

been in talks with several governments about procuring vaccines

since 2022. Those requests have accelerated with the U.S.

outbreak, she said.

PREPANDEMIC STOCKPILE

The U.S. maintains a stockpile of prepandemic vaccine

candidates and bulk vaccine against an array of influenza

strains and conducts clinical trials to support an Emergency Use

Authorization or FDA license in the event of pandemic.

Seasonal flu vaccine makers, including Sanofi,

could also be asked to shift to producing pandemic flu vaccines.

The U.S. is in talks with mRNA vaccine makers Pfizer ( PFE )

and Moderna ( MRNA ) about potential pandemic vaccines.

Dr. Richard Webby, a St. Jude Children's Research Hospital

virologist who studies flu in animals and birds for the World

Health Organization, said the situation in dairy cattle merits

vaccine use.

"If we look at the exposure levels that some of these

farmers are getting, it's high," Webby said.

The decision on how and when to use the vaccine will hinge

on evidence of increased transmission, severity of disease,

cases in people with no link to a dairy farm and mutations in

the virus, U.S. Centers for Disease Control and Prevention

Principal Deputy Director Nirav Shah said.

Dutch flu virologist Ron Fouchier of the Erasmus MC in

Rotterdam, who has conducted experiments mapping the changes

necessary for bird flu to spark a pandemic, said Europe's plan

is to procure the CSL vaccine for people occupationally exposed

to the virus.

His lab could well be eligible if a vaccine becomes

available, he said, adding, "I would certainly take it."