Smallpox - how worried should we be?
The recent announcement that the government expects to vaccinate key health workers against smallpox as part of its contingency plan for dealing with a bio-terrorism attack might leave lesser mortals wondering where they fit into these plans.
The Department of Health's decision makes sense - we need immune medical staff to effectively tackle any outbreak, no matter how unlikely. But it has inevitably caused concern among some members of the public.
Are we really at risk from terrorists releasing the smallpox virus in one of our cities? And what effect would that have? What is smallpox anyway?
A remote possibility
The first thing to note is that the likelihood of a terrorist group getting its hands on the virus is extremely small. It was eradicated in 1980 after a worldwide vaccination programme and remains only in two special high-security facilities - one in the US and one in Russia.
There is still a remote possibility, however. The director of the Center for Civilian Biodefense, in the US, Dr Tara O'Toole, recently explained, "Smallpox is arguably the least available potential biological weapon, but the real wildcard is we don't know the fate of all of the many tonnes of smallpox the Soviets created in the 1970s and 80s."
Although unlikely, it is the effect the smallpox virus would have in the wider population that has terrified Western governments. Millions of people were vaccinated in the 1960s and 70s, but the vaccine is only thought to last on average 10 years. Therefore most of the population and certainly anyone under 30 is unprotected.
Smallpox has an incubation period of around 12 days. Even then the first symptoms can easily be misdiagnosed as flu. Few doctors will have seen smallpox first-hand. It is contagious. It is incurable. It killed more people last century than the two world wars put together. It causes extremely painful pus-filled blisters and those who contract it may bleed to death from internal haemorrhaging. It kills a third of those who get it.
And now the good news
However, do not flee for the hills just yet. Those given the smallpox vaccine before being infected will be fine and those given it within four days of infection have a hugely increased chance of survival.
Dr Richard Harling, an expert at the Centre for Communicable Disease Control, part of the Public Health Laboratory Service in London, adds that smallpox is not as virulent as people tend to think. "It is not easy to release," he says. "If someone with it just breathed near you, you wouldn't catch it. It's people in the same household that tend to be at most risk. Smallpox is more like TB than measles, you have to be quite close to someone for quite a long time."
And forget about virus bombs. "If it was put in a bomb, the virus would risk being destroyed by the heat," Dr Harling explains.
The only problem is that there aren't enough vaccines to go round. The UK government has been characteristically secretive about how many vaccines we actually have, although journalists recently reported there were 3.65 million. Theoretically, this could be split up to vaccinate 14 million people - out of a population of around 60 million.
However, in April, the government followed in the footsteps of the US, and ordered a further 30 million vaccines at a cost of £32 million.
Search and contain
There remains some argument over the (secret) contingency plans, however. Chief Medical Officer Sir Liam Donaldson says the government's policy is "search and contain" - only vaccinating those around the source of the outbreak. Others, however - most notably Labour MP and chairman of the Commons science and technology committee Dr Ian Gibson - have called for the whole population to be vaccinated.
Dr Harling rules out a nationwide vaccination programme. The approach we have is the same one the World Health Organization used in the 1960s and 70s to eradicate the disease, he explains. You vaccinate the people near to whoever is infected and then those who are close to them such as friends and family.
"It has nothing to do with costs and everything to do with what works and with prioritisation," he says.
And then there is the risk of the vaccine itself. Pregnant women and people with weak immune systems or eczema should not be given the injection and a small percentage of the population will have an adverse reaction to it.
A recent study suggested that if 80 million people under 30 were vaccinated, 200 of them would be likely to die. While a smallpox attack remains a distant possibility, it would be impossible to justify such an approach. Besides, if we had a vaccine for every possible bio-terrorist disease, we'd never be out of the doctor's.
Dr Harling is not unduly concerned about the risk of an outbreak. "Smallpox is extremely difficult to get hold of and to disseminate," he says and adds that terrorists are far more likely to use pathogens that are easier to find and just make people very sick.
"Things like salmonella are far more likely," he says. "It causes a lot of illness and can cripple a small economy and be difficult to trace."
Department of Health
Public Health Laboratory Service