25 March 2003

Smallpox Bioterrorism Unlikely: 
Populations are easily protected

Professor John Oxford

St Barts & The London Hospital
Queen Mary’s School of Medicine and Dentistry, Medical Sciences Building, 327 Mile End Road, London, E1 4NS

The deliberate release of Anthrax spores in the USA has emphasised how vulnerable modern city communities are and also how panic can easily grip a society, leading quickly to economic and social problems. Anthrax does not normally spread from person to person and antibiotics can be used very successfully to treat or prevent illness and so, in reality, it is rather an ineffectual weapon. In many ways smallpox is also a poor choice for a terrorist, although the mere thought of an outbreak can have immense repercussions. The virus is of low infectivity, and with such a long incubation period people can be vaccinated even after infection.  In contrast, influenza and measles are highly infectious and can spread like wildfire. Also reassuring is the fact that around one third of the population of the UK will have already been vaccinated in the last century. 

Terrorists are calculating people and tend to use the most effective and easily-obtained weapon: high explosive.  Smallpox, in contrast, needs a special laboratory in which to be nurtured, even if one could get one’s hands on the virus.  Officially, it is only held in two places, Siberia and Georgia (USA).  Though there have been unsubstantiated rumours of a theft of smallpox from the Russian Vector Institute about fifteen years ago, on a recent visit I witnessed heavy security provided by the Russian army. Security at CDC is also tight.  There is a standing committee of virologists which, on behalf of WHO, overseas all and every experiment, carried out in one of the two registered centres.  Though a previous WHO advisory committee had recommended destruction of the final virus stocks, this has not happened as there is still much to be learned from this most complex of all viruses.

In Europe as a whole in the 20^th Century very few imported outbreaks resulted in more than a few dozen cases of the disease. One notable exception to the argument outside Europe relates to an outbreak in Iran, which spread to other countries and is thought to have involved 8000 cases, of which 2000 were hospitalised. There were five outbreaks in the UK in 1961-1962 but only 62 cases of smallpox were recorded with 25 deaths.  Recognising the risks of vaccination, the UK responded using 100,000 vaccine doses in a ring vaccination exercise, focusing on the immediate family and friends of the first cases. The last outbreak I personally remember in Wales was well controlled in this way. I was vaccinated myself in the programme and had to spend a week in bed overcoming the side-effects. In his book Scourge, Jonathan Tucker noted that 5.5 million people were vaccinated in this outbreak, and complications from the vaccine caused at least 18 deaths.

In contrast, because of public pressure in Yugoslavia in 1972, virtually the whole country was vaccinated, 18 million out of a population of 20.8 million. That involved 175 cases of smallpox and 34 deaths from the disease. The vaccine caused fifteen deaths, 97 people were severely ill, and another 154 were made mildly ill. In 1947 a small outbreak of smallpox in New York City triggered widespread panic, forcing city health officials to launch a month-long campaign in which 6.3 million people were vaccinated. Two people died from smallpox, six people from adverse reactions to the vaccine.

Today the UK government strategy is to stockpile vaccine and wait for something to happen.  This is an eminently sensible and thoughtful strategy.  By far the most likely scenario is that smallpox will never be seen in the community again.

In essence, the plan is to establish a small well-trained cohort of doctors, scientists and nurses in the UK who could identify and isolate a smallpox case and start a ring-fence vaccination. Eventually, enough vaccine is to be stored to immunise the whole population, but at present there is an ample supply at 20 million doses.

Virologists are working to make a new generation smallpox vaccine that will be much safer, and the UK is well in the vanguard of these efforts.  Then, if populations choose to be vaccinated they could have the comfort of protection against smallpox without the risk of life-threatening side effects. 

We may eventually look back with bemusement on this strange interlude when public health strategies became muddied by international politics, and at least decide that we were taught a lesson that hysterical responses and talking up of threats help no-one.