The World Health Organisation has said that healthcare workers should get priority access to vaccination against H1N1 swine flu.
Dr Marie-Paule Kieny, WHO director of the Initiative for Vaccine Research, reiterated the message that the virus was "unstoppable" and all countries would need access to a vaccine.
She said healthcare workers should be the main priority group for vaccination, to protect them from the risk of infection, and to ensure they could continue to treat patients with a range of illnesses.
Her comments came as news emerged of the death of the first healthcare worker in the UK with swine flu.
Dr Michael Day, a GP, died on Saturday in the Luton and Dunstable Hospital. A swab test showed that he had the virus, but the exact cause of death has yet to be established.
Paying tribute to Dr Day, the chief medical officer for England, Sir Liam Donaldson said: "It is a very sad case. He was a very dedicated doctor, loved by his patients."
He added, " It won't be much more than a relatively mild illness for most people and not everyone will get it in the first wave of attacks. In past experience of pandemics its been no more than 30-35% of the population and then in succeeding flu seasons others get it". He said this made vaccination very important.
Dr Day's death, together with that of a six-year-old girl brings to 17 the number of fatalities linked to the virus in the UK. Chloe Buckley, from north west London died on Thursday. A post-mortem examination will be carried out to determine if she had any underlying health conditions.
Dr Marie-Paule Kieny, presented feedback from a meeting on 7 July of SAGE, the Strategic Advisory Group of Experts on Immunization, who advise the WHO and member states.
She added that, in no particular order, other priority groups for vaccination would be pregnant women, anyone over six months with chronic health conditions such as respiratory problems, healthy adults under the age of 49, healthy children and healthy elderly people. Clearly this includes whole populations so governments will have to decide which groups to protect first.
Dr Kieny said that obesity had been noted as a risk factor but experts are unsure whether it is obesity itself or the health conditions that arise from it. People with a BMI (body mass index) of over 30 and especially over 40 had been noted as having a higher chance of severe disease.
Problems with vaccine yield
Dr Kieny said vaccine yields had so far been poor but manufacturers were looking at alternative strains which might increase output. Most flu vaccines are grown in eggs and it seems that H1N1 swine flu is producing less yield than other seasonal flu strains.
"Some strains are good yielders and some are bad," said Dr Kieny.
"It is not a severe problem yet," she added, as the production is enough to do the clinical trials needed to test the vaccine and other, better yielding strains may emerge. These will be generated from the WHO laboratory networks around the world having isolated samples from patients with the virus.
So Dr Kieny sounded a note of reassurance, but if the low yield continues, then it would spell problems for the amount of vaccine that could be produced.