Immune-suppression must while planning for smallpox outbreak

Unprecedented levels of immunosuppression in countries like Australia and the US must be considered in planning for the real risk of smallpox re-emerging in the world, a study warns.
"Smallpox was eradicated in 1980 but in 2017, Canadian scientists created a smallpox-like virus in a lab using just mail order DNA," said Raina MacIntyre from University of New South Wales in Australia.
"Now in 2018, these same scientists published a step by step method to create a pox virus in a lab, making the threat of smallpox re-emergence even greater," said MacIntyre.
In the nearly 40 years since smallpox was eradicated, much has changed in society.

Advances in medicine mean that many more people today live with a weakened immune system - such as people with HIV, people being treated for cancer and autoimmune conditions.
The study, published in the journal Emerging Infectious Diseases, showed that children and young people aged 0-19 years will have the highest risk of infection in a smallpox epidemic. However, the risk of severe disease and death is in people aged more than 45 years.

Almost one in five people in cities like Sydney and New York have a weakened immune system, which would make the impact of an attack with smallpox much more severe, according to the study.

"The rates of immunosuppression were even higher for the age group 60-65 years, because of natural decline of the immune system with age," MacIntyre said.
"We have an ageing population, and this must be considered when planning for a bioterrorism attack, and vaccination strategies during an outbreak," MacIntyre added.
She has led a study that used a mathematical model to identify the impact of smallpox re-emerging in cities like Sydney and New York.
The research identified that the highest rates of smallpox infection in these cities would be in people aged under 20 years, but the highest death rates would be among people aged 45 and over.

The study also is a tale of two cities with very different vaccination policies. Smallpox vaccine was routine in New York, but not used widely in Sydney.
MacIntyre said almost 22 per cent of the current New York population is vaccinated for smallpox, compared with only 10 per cent of the current Sydney population - and these were mostly migrants who were vaccinated in their country of origin.
The research therefore looked at whether past vaccination in older people gave much protection.
Despite widespread past vaccination in New York, the modelled impact of smallpox in this city was more serious than in Sydney due to its larger number of immunosuppressed people.

"Immunosuppression would likely drive the impact of smallpox more than past vaccination, especially with so many people today living with HIV, or receiving cancer therapy or other medical treatments that suppress the immune system," said Tony Kelleher from University of New South Wales.
"Vaccine immunity wanes over time, and recent vaccination is needed for protection. The good news is, people who have been vaccinated in the past would have a faster response to re-vaccination in the event of an outbreak," MacIntyre said.
"The bad news is, both cities show the highest smallpox infection rates for unvaccinated young people, aged 5-20 years," she said.