Dr David Cavanagh : Vaccination is key weapon in battle against virus

VACCINATION is a very effective way of protecting against disease. But no vaccination campaign ever has been 100 per cent effective. That is why herd immunity is so important. If you get 95 per cent coverage in, for example, measles vaccination, you don't get any measles because the chances of an infected person meeting an non-immunised person are small, and so the virus can't spread. There are not enough non-immune people in the population for the disease to spread easily.

When vaccine coverage drops, that is when you start to get measles cases.

For swine flu, the obvious risk groups who should receive the vaccine as a priority are the young and the old. With seasonal flu, most deaths tend to be in the young and the old. That is standard thinking about swine flu generally. In the current outbreak, the majority of people who have died are those with pre-existing medical conditions. It does not seem to have caused many deaths in people who are relatively healthy.

People with respiratory conditions, pregnant women and those with other relevant health problems should also be made a priority.

At the moment, the virus is not taking off in huge numbers. That will probably happen in the autumn once the weather gets colder and children return to school.

We do not yet know whether this new strain of flu is going to be worse than the seasonal flu outbreaks we get every year. That is just because it is a new virus and it may mutate and therefore spread more easily and cause more disease. At this stage, it is too early to know if it is going to be really bad. But everyone is working hard, and I am sure they will have an effective vaccine soon.

Companies have a standard procedure for making normal flu vaccine every year. The same methods will be used to produce the new vaccine. It will be tested using the same methods and same systems and will be just as safe. Influenza vaccines have a very good safety record.

Vaccination generally has been one of the most effective health measures we have ever had. If you look at what we have done against measles, polio and smallpox, vaccination is relatively simple and very effective in reducing deaths and illness against a whole range of diseases.

People forget measles is probably the fourth-biggest infectious disease killer in the world, and the reason it kills so many people is because vaccination in areas such as Africa and Asia is quite often not available. This should send out a message of just how important vaccination can be.

• Dr David Cavanagh is a lecturer in immunology at the University of Edinburgh.