Smallpox protection plan inadequate: study
Researchers have found that mass vaccination against smallpox in the US would prevent more deaths in an outbreak than the existing containment plan.
The results come on the heels of reports that the US is planning to vaccinate half a million health workers against smallpox.
The study, published in the Proceedings of the National Academy of Sciences (PNAS), used a mathematical model to compare different responses to a smallpox attack on a city with 10 million inhabitants.
The scientists considered the number of people initially infected, the transmission rate, the fraction of potential contacts named by infected individuals, and the resources available to track potential contacts and administer vaccinations.
The best approach was mass vaccination, the model predicted. A mass vaccination campaign before an attack would slow the spread of infection most effectively, resulting in 4120 fewer deaths than the current plan.
The existing plan, endorsed by the US Centers for Disease Control and Prevention (CDC), calls for quarantine of confirmed smallpox cases, targeted vaccination of those who have been in contact with infected individuals, and mass vaccination only if the initial methods do not work.
Australia's current policy reflects a similar approach, said Acting Chief Medical Officer Professor John Mathews in a written statement. It calls for 'ring' vaccination of people in close proximity to smallpox cases.
The US researchers acknowledge that such methods called 'surveillance-containment' are widely credited with the elimination of smallpox worldwide. This was achieved in 1979 after a long campaign by the World Health Organization (WHO). Fears of bioterrorism have arisen from reports that samples of the smallpox virus officially kept only in high-security labs had fallen into the wrong hands.
But a surveillance-containment strategy is less likely to work in current circumstances, say the US researchers. An attack on New York City in 2002 will result in a far higher potential transmission rates than were typical in the late 1970s, when the last cases of smallpox occurred in small isolated villages that already had some level of vaccination.
According to Professor Mathews's statement, "Australia is fully aware of the difference of views of around the world about smallpox vaccination strategies and of the arguments as such in the article."
He disagreed with the suggestion that mass vaccination would be preferable, pointing out that the smallpox vaccine carries a risk of side effects. Potential complications include encephalitis and even death in a small number of cases.
"Australia has considered these matters carefully and is regularly in touch with counterparts overseas and our current policy of using vaccine of ring vaccination is aligned with the WHO, the CDC and the United States Health Department," Professor Mathews said.
Smallpox can kill up to 30 per cent of people who are infected. After an incubation period of about 12 days, fever, aching and fatigue begin, followed by a rash that develops into lesions over the face, arms and legs. The lesions take three to four weeks to fall off.
The virus is transmitted in saliva from face-to-face contact, putting close family at most risk. The stability of the virus in aerosol form and the small dose necessary for infection dose make it ideal for biological warfare.
Vaccination within four days of exposure can lessen the severity or prevent the illness.
But is there enough vaccine available if an outbreak did occur? Professor Frank Fenner, a world authority on smallpox, thinks there is, at least in America.
"Supplies in the US were very limited, until it was found that it was possible to dilute the stocks that were available quite substantially and still get good reactions," he told ABC Radio's PM program.
"Further stocks were ordered and there are now about 160 million doses available. It was expected within the year that 250 million doses will be available enough to vaccinate the whole of the US."
In a statement last October, following a number of anthrax cases in the US, Australia's Chief Medical Officer Professor Richard Smallwood said that the risk of a smallpox attack in Australia was low.
At that time, Australia had no smallpox vaccine, the statement said, but the Department of Health was negotiating to obtain supplies.
The World Health Organization has pledged to support any country in controlling smallpox because it would be considered an international emergency.