By Fergus Walsh
BBC News Medical Correspondent
Are you a front-line medical worker like a GP or a hospital nurse? Or maybe a police officer, or even a key worker at a power plant?
The UK government has bought 2m doses of the vaccine
If so, then a prototype vaccine against H5N1 developed in Vienna could be destined for you.
It's an experimental vaccine against bird flu.
Two million doses of this prototype vaccine have been sold to the UK government.
Dr Noel Barrett, of Baxter Healthcare in Austria, says: "This vaccine formulation is our best shot to produce a good immune response which will protect against a multitude of different strains, even the strain which may cause a pandemic.
"We have animal studies which indicate it gives good protection."
It is made by injecting the wild H5N1 virus into animal cell cultures.
The vaccine is then fermented in large steel tanks before being purified.
The virus is inactivated or killed - so it can't cause infection in humans.
The whole process takes three to four months.
That may seem like a long time, but it is much quicker than the traditional way to make flu vaccines, done by growing the vaccine strain in fertilised hens' eggs.
So when will people start being immunised with the prototype vaccine? It's impossible to answer that question at present.
It will be used only if a flu pandemic is triggered by the H5N1 virus or looks highly likely.
And the British government hasn't worked out exactly who will get it beyond front-line medical workers. It says that it will go to "priority groups".
We should not get alarmed about bird flu. After all, this virus causes disease almost exclusively in animals.
But it has infected nearly 200 people in the past three years and killed around half of them.
Fortunately, it is almost impossible for it to be transmitted between humans. Those who have been infected have had direct contact with sick birds.
Why then do we need a vaccine? Well sooner or later, bird flu is expected to become humanised.
Then we will have what's called a flu "pandemic", or a global outbreak of disease.
When that happens the world will clamour for an effective vaccine against the pandemic strain of flu.
If you are really worried about bird flu then now might be the time to consider a change of career - if you can work out what job fits into the government's "priority groups" category.