Four in 10 US health professionals will stay away from work in the event of a flu pandemic, a study says.
The world is overdue for a flu pandemic
Researchers from Johns Hopkins School of Public Health in the US and Israel's Ben-Gurion University quizzed over 300 US health staff.
They said if so many stayed away it would undermine the emergency response, BMC Public Health journal reported.
But experts said UK health workers were fully prepared to work through a flu pandemic.
Scientists have warned the world is overdue for a flu pandemic with the most likely cause being if bird flu mutates with a human form of the virus.
Health workers are expected play a key role in most countries in such an event.
In the UK, GPs have been sent information packs about what they need to do in response to an outbreak.
The government is stockpiling 14.6m courses of antiviral drug Tamiflu, which is not a cure for pandemic flu but alleviates its symptoms and slows its progress. Health workers have been told they will be the first to receive it.
Ministers have also promised to buy in enough vaccine to treat the entire population.
The government estimates GPs are likely to see as many as 14m more patients during a pandemic than normal, while hospitals will see a 50% rise in admissions for acute respiratory conditions.
The researchers found clinical staff such as doctors and nurses were more likely to say they would report to work than technical and non-clinical staff.
Workers said their motivation was fear of contracting the virus and the perception that their role in fighting it was not that important.
Lead author Ran Balicer said: "Current preparedness plans account for some personnel shortages mainly due to illness from influenza.
"The public health workforce will play a critical role in managing an influenza pandemic, but the workforce is not yet prepared for this crisis.
"We need more training for public health workers, particularly for those in technical and support roles."
But experts involved in emergency planning in the UK said British health workers were fully prepared.
A spokeswoman for the Emergency Planning Society, which represents health and local government staff, said: "There have been no suggestions that staff will not turn up for work during a pandemic.
"Past experience suggests that during major emergencies, UK health workers and other emergency staff rise to the challenge. I don't think it will be any different this time.
"Anti-viral drugs have been ordered, so protection is being put in place. I can't see what they say will happen in the US happening here."