WASHINGTON – The Biden administration, keeping a watchful eye on an outbreak of avian influenza that has led to the deaths of tens of millions of chickens and is driving up the cost of eggs – not to mention raising the frightening spectre of a human pandemic – is contemplating a mass vaccination campaign for poultry, according to White House officials.

The bird flu outbreak, which began early in 2022, is the biggest in the United States’ history, affecting more than 58 million farmed birds in 47 states, and birds in the wild.

It has already spilt over to mammals, such as mink, foxes, raccoons and bears, raising fears that the virus that causes it, known as H5N1, could mutate and start spreading more easily among people.

Experts at the Centres for Disease Control and Prevention (CDC), whose focus is human health, say the risk of a pandemic is low.

As a precaution, the agency has sent drug manufacturers flu virus samples that could form the basis of vaccines for people. The CDC is also exploring whether commercial test manufacturers would be willing to develop tests for H5N1, similar to those used for the coronavirus.

Bird flu infections in humans are rare, and transmission of bird flu between humans is extremely rare.

Worldwide, there have been nine H5N1 cases reported in people since the beginning of 2022, according to the World Health Organisation.

In Cambodia, an 11-year-old girl recently died from H5N1 and her father was also infected with it, though the virus was a different version from the one circulating in birds in the US.

Cases typically involve people exposed to poultry. In the US, the CDC, in partnership with state and local public health departments, is monitoring people exposed to H5N1.

As at last week, 6,315 people had been monitored; 163 reported symptoms; and one tested positive, according to Dr Tim Uyeki, chief medical officer of the CDC’s influenza division.

At the same time, officials at the federal Agriculture Department, which is responsible for the health of farm animals, say they have begun testing potential poultry vaccines and initiated discussions with industry leaders about a large-scale bird flu vaccination programme for poultry, which would be a first for the US.

Farm birds are already vaccinated against infectious poultry diseases, such as fowlpox. But an avian influenza vaccination programme would be a complex undertaking, and poultry trade associations are divided over the idea, in part because it might spawn trade restrictions that could destroy the US$6 billion (S$8.1 billion) poultry export industry.

Dr Carol Cardona, an expert on avian health at the University of Minnesota, said the fear of trade bans was a huge barrier to the mass vaccination of poultry.

“This is the undeclared war – trade,” she said.

Avian influenza experts, however, say they believe the Biden administration should move ahead with a vaccination campaign, in part to reduce the risk of a human pandemic. In interviews, several called for the administration to act quickly.

“My own opinion is under the present circumstances, we should be vaccinating the poultry population of the United States against H5N1 – absolutely,” said Dr Robert Webster, an expert in avian influenza at St Jude Children’s Research Hospital in Memphis, Tennessee. Such a campaign could “prevent the inevitable transmission to humans”, he said.

For President Joe Biden, there are also political considerations at work. Egg prices, which soared in 2022, were 70 per cent higher in January than they were a year earlier. Those high prices have given Republicans another opportunity to attack Mr Biden over inflation just as he is preparing to run for re-election in 2024.

Experts have long worried that a human-adapted version of bird flu could set off a global pandemic. For that reason, the US and the world need to be doing more to prepare, said Mr James Krellenstein, an adviser to Global Health Strategies, an international consulting firm.

Mr Krellenstein and Mr Garrett Wilkinson, a health policy expert at the non-profit Partners in Health, examined the world’s readiness for an H5N1 pandemic and identified several “important gaps”, according to a report they shared with The New York Times.

With a two-dose regimen, the US could need at least 650 million doses of H5N1 vaccine for use in humans, and the report said it was unclear how the country could reach that figure with its current manufacturing capacity.

“While it is extremely important that serious efforts are taken to bring the outbreak in domestic and wild birds under control, the reality of the situation is serious enough that we must be taking more steps to prepare for a possible human outbreak of this virus,” Mr Krellenstein said in an interview. “We should be viewing this as a live-action fire drill.”

Before Covid-19, many experts predicted that the next pandemic would be caused by influenza.

In 2020, the federal Department of Health and Human Services published a 10-year strategy for updating influenza vaccine production; a White House official said the Biden administration was reviewing the document in the light of the outbreak in birds.

One step towards pandemic preparedness, many experts agree, would be a poultry vaccination campaign.

“Just having the virus be less widespread would reduce the exposures to humans,” said Associate Professor Anice Lowen, an influenza virologist at Emory University, adding that a vaccination effort “would also reduce the potential for viral evolution” that might enable the virus to spread efficiently from person to person.

Federal regulators have not yet authorised the vaccination of poultry against highly infectious bird flu strains like H5N1, said Mr Mike Stepien, a spokesman for the Agriculture Department. While there are several licensed vaccines, it is unclear whether any of them are effective against the current strain, he said.

Scientists at the department have been working to develop vaccine candidates in-house, said Dr Erica Spackman, a research microbiologist at the agency’s Agricultural Research Service, who is one of the scientists leading the testing of the poultry vaccines.

Dr Spackman and her colleagues are aiming to test multiple potential vaccines – including those already licensed and the new vaccine candidates – in chickens, turkeys and domestic ducks, she said.

Beyond the science, there are economic considerations. The US is one of the world’s biggest exporters of poultry products, and its trading partners want assurances that they are not importing meat from infected birds. Vaccination could make it more difficult to prove that birds had not been infected.

Broilers – the industry term for chickens raised for their meat – account for the vast bulk of exported poultry, said Dr Amy Hagerman, an agricultural economist at Oklahoma State University. So it is perhaps not surprising that the National Chicken Council, which represents the broiler industry, opposes vaccination.

“Although initially appealing as a simple solution to a widespread and troublesome problem, vaccination is neither a solution nor simple,” said Mr Tom Super, the council’s senior vice-president for communications.

He said that the broiler industry exported 18 per cent of its meat and that losing the ability to export chicken would cost it “billions and billions of dollars”.

But the turkey sector, which has been hit hard by the virus and exports just 9 per cent of its meat, is open to vaccination.

“We recognise that unilateral vaccination would have a severe impact on exports,” said Mr Joel Brandenberger, the president of the National Turkey Federation. “At the same time, we have urged and continue to urge the federal government to move as rapidly as possible to try to develop new agreements” with trading partners.

Avian influenza is typically carried by waterfowl and shorebirds, which pass the virus to poultry through their faeces or respiratory secretions.

During past outbreaks, officials have stamped out the virus by tightening biosecurity measures, quarantining affected farms and culling infected flocks. But with the virus now unusually widespread in wild birds, those steps have failed to contain the spread.

A handful of countries in which avian influenza is endemic, including China, Egypt and Vietnam, already routinely vaccinate poultry against it.

The vaccines are typically injected into individual birds and require more than one dose, said Dr Leslie Sims, an international veterinary consultant on the prevention and control of zoonotic diseases who is based in Australia.

Although the cost varies, it can be as low as a few cents per dose, he added. NYTIMES