Weaponised smallpox virus could infect thousands in major cities
15 March 2018 • 11:39am A
weaponised smallpox virus could have a devastating effect on the world's
major cities, infecting thousands because of the growing numbers of
people with suppressed immunity, researchers have warned.
Smallpox, which was eradicated globally in 1980, is classed by the
United States government as a category A bioterrorism agent because of
its potential to spread rapidly, infect swathes of the population and
incite widespread fear and panic.
Researchers at the University of South Wales have used a mathematical
model to predict how many people would become infected and how many
would die in bioterrorism attacks on New York and Sydney.
The data is likely to be scrutinised carefully by public health
officials in Britain in the wake of the attack on Salisbury last week.
Russia is known to hold samples of the smallpox virus.
Raina MacIntyre, professor of infectious diseases epidemiology and
lead author of the study, said that since smallpox was wiped out, the
population has changed greatly with many more people living with
conditions that suppress their immunity. They would be particularly at
risk of catching and therefore spreading the disease, she said. "The change in medical immunosuppression since 1980, when smallpox
was eradicated, is huge. Diseases like HIV were virtually unknown at the
time. The first heart-lung transplant had not yet occurred –
transplantation medicine has progressed in leaps and bounds.
"We also have an ageing population, with age-related decline in
immunity, and many more drugs for the treatment of cancer and autoimmune
diseases which suppress immunity. No other model of smallpox has
accounted for this," said Professor MacIntyre.
The researchers estimated that
about one in five people in New York and one in six in Sydney have
lowered immunity but say these are probably conservative estimates.
Large-scale smallpox vaccination programmes ended in the 1970s
meaning that there is also very little immunity in the general
population.
The researchers put in place a scenario based on the smallpox virus being released in a crowded place, such as an airport, and then worked out how it would spread and its effect on the population over 100 days.
They calculated that an outbreak would peak at 70 days after the
first case, by which time it would have infected around 4,200 people in
New York, killing around 1,200. In Sydney, around 2,200 people would be
infected, with more than 600 deaths.
Professor MacIntyre said that high levels of immunosuppression have
not been considered in planning for smallpox attacks, with emergency
planning still "rooted in the past".
She added that the implications for London would be the same as for
New York and Sydney, as it has a similar number of immunosuppressed
individuals - about 17 to 20 per cent of the population.
"Large cities are at the greatest risk because of high population
density, rapid spread of infection and greater difficulty in contact
tracing of exposed people," she said.
She urged authorities to start
thinking about which vaccines could be used on which populations and how
fast an outbreak could spread, given the high numbers of people with
suppressed immune systems.
Commenting on the research, Amesh Adjala, an infectious diseases
expert and senior scholar at the Johns Hopkins Center for Global Health
Security, said the prospect of smallpox attack would be a “national
security event without precedent”.
“It’s considered a major threat. The virus has been eradicated from
the planet and only exists in designated repositories in the United
States and Russia. It’s something people have thought about as a
bioterrorism agent and that’s why the US government has put in so much
effort to develop new vaccines,” he said.
Authorities would most likely tackle a smallpox epidemic with a
technique called ring vaccination, where the contacts of those infected
are vaccinated to form a ring protecting the rest of the population,
said Dr Adjala.
However, he added that people with lowered immune systems would not be able to have the standard vaccine.
“With smallpox there has been an effort to develop new generation
vaccines that are safe to use in the immuno-suppressed population. In
the US they’re not yet licensed to use however they are stockpiled in
the strategic national stockpile. In the event of an outbreak they would
probably be given an emergency use authorisation,” he said.
The World Health Organization has stockpiled around 30 million doses of first, second and third generation vaccines.
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