Channel 4 UK Q&A on swine flu

The UK’s Channel 4 News website asked leading experts to answer questions about swine flu. The Q&A is available in full here.

An excerpt from the latest Q&A:

Is there any official estimate of the expected number of deaths?

Meirion Evans: The Department of Health has published planning assumptions about swine flu, although these are not intended to be predictions. Currently, the death rate is thought to be around 1 out of every 1000 people who get swine flu.  There is no official estimate of the expected number of deaths because of the difficulty in predicting how many people will eventually be infected with swine flu and how severe the illness might be in the autumn.

John McConnell: Official estimates for the UK range between 3100 and 65000. The lower end being equivalent do deaths in a winter of mild seasonal flu, and the upper end being equivalent to two or three severe winters of seasonal flu.

Andrew Easton: The estimates can only be expressed in terms of the possible range that MAY occur.  This is because it is necessary to extrapolate from the current knowledge and inevitably there is a degree of uncertainty in doing that.  As the number of cases increases the degree of uncertainty reduces.  It is important to appreciate that what this means is that the figure at the bottom of the predicted range is equally as likely as the figure at the top of the range, though the latter generally gets more attention.

Once you have had swine flu, whether mild or severe, are you then immune to it? If you are immune would you still be immune if it mutates?

Meirion Evans: Yes, you will be immune regardless of how mild or severe your symptoms. Unless there are very substantial changes in the virus, this immunity is likely to protect you even if the virus mutates.

John McConnell: Yes; and not necessarily, since it will depend on the degree of mutation.

Andrew Easton: After infection you will be immune to reinfection with that virus.  If the virus mutates in a way that allows it to avoid the aspects of the immune system that provide immunity you would then be susceptible to a second infection.  That is the basis for people being infected with seasonal flu in successive years – the virus has altered sufficiently in the intervening period to be able to avoid the immunity that had been established.

Is there an end point? If it follows current predictions what happens in the next 3 – 5 years? Does the effect dwindle as we build immunities? Or is it here to stay

Meirion Evans: Past pandemics have generally occurred in two or three large peaks over 12-18 months. Thereafter, while the virus may continue to circulate in the population for some years to come, the numbers of cases become progressively fewer because most people are immune.

John McConnell: An end-point will be reached once transmission of the virus is interrupted because a sufficient proportion of the population is immune to infection. Immunity may be acquired naturally or by vaccination. This endpoint might be reached within less than a year in the UK once vaccine is available, but might take 2-3 years in countries too poor to afford vaccine. As with most infections, the world’s poorest people will suffer the greatest burden of sickness and death.

Andrew Easton: The pattern that has been seen with all previous flu pandemics is that the virus infects a very large number of people in the first year or so after its appearance.  These individuals become immune to that specific virus.  In subsequent years the virus appears as a seasonal flu, infecting individuals who have not become immune.  At the same time the virus mutates very gradually to become sufficiently different that it can then infect some of the previously immune individuals.  The virus is then established as a seasonal flu, reappearing every year and each time changing very slightly.  The expectation therefore is that this virus should establish itself as a seasonal flu.  In the coming months a very large proportion of people in the world will become infected (and will become immune).  The virus will then mutate in the way that all flu viruses do and will be able to spread in communities.