Smallpox data suggests a tiny amount of virus may IMPROVE survival

What 300 years of smallpox epidemics in London can teach us about Covid-19: Infection with a small amount of virus can IMPROVE survival rates — and might be a beneficial side-effect of wearing masks

  • Researchers from Canada analysed London death records from 1664–1930
  • This covered the introduction of health measures, variolation and vaccination
  • The period ended with the last case of the fatal and scarring disease in the city 
  • Variolation saw people inoculated with small amount of virus from the infected
  • The procedure — which had risks in its use against smallpox — was abandoned
  • Experts have said wearing masks may help safely variolate against COVID-19

Infection with a small amount of virus — such as may be a side effect of wearing face masks — may improve epidemic survival rates, a historical study found.

Researchers from Hamilton, Canada studied thousands of weekly records detailing London’s smallpox fatalities during the years 1664 to 1930.

Their findings provide fresh insights into the development of infectious diseasing — showing how changing conditions impacted outbreak rates and severity. 

Smallpox — which killed 30 per cent of those it infected, and let many others blind or disfigured — was one of the most devastating viruses to have struck humankind.

The disease initially caused fever and vomiting, followed by mouth ulcers, a skin rash and finally characteristic, dimpled blisters that scab over and leave scarring behind.

It is one of only two diseases to ever have been successfully eradicated — with the other being rinderpest, which infects cattle and thus impacts human food supplies. 

Researchers from Hamilton, Canada digitised and studied thousands of weekly records detailing London’s smallpox fatalities during the years 1664 to 1930, pictured above

‘The current COVID-19 pandemic has caused a surge of interest in the study of infectious disease transmission and how public health interventions could change the course of the pandemic,’ said mathematician David Earn of McMaster University.

‘Our goal was to describe and make publicly available the weekly time series of smallpox mortality in London — and to identify historical events that might have influenced smallpox dynamics over the centuries.’  

In their study, Professor Earn and Olga Krylova, also of McMaster, digitised more than 13,000 weekly smallpox mortality records which had been published in the London Bills of Mortality and the Registrar General’s Weekly Returns from 1664 to 1930.

This data spans an era starting before any form of public health practises were in place, through to the introductions of both variolation and later vaccination — and concluding with London’s final smallpox death.

Variolation was a procedure in which doctors tried to inoculate the healthy by exposing them to smallpox virus taken from the pustule or dried scab of an infected person, rather than with milder cowpox virus, on which the vaccine was later based.

‘During the time period covered by the data, smallpox changed from a terrifying and unavoidable danger to an easily preventable infection,’ said Professor Earn.

‘Introduction of better control measures, especially vaccination, naturally led to decreased smallpox mortality and eventually eradication.’

Dr Krylova added: ‘It is clear that the introduction of smallpox control measures — variolation and later vaccination — made eradication possible.’

‘Our analysis also suggests that greater use of control measures and changes in public health policies were correlated with changes in the frequency of the epidemics,’ she said.

The practice of variolation for smallpox was abandoned, as it had the potential to lead to serious and fatal infections, and could trigger new epidemic outbreaks.

However, experts have recently suggested that variolation with small amounts of the virus behind COVID-19 may be a beneficial side-effect of the use of face masks.

The duo digitised more than 13,000 weekly smallpox mortality records which had been published in the London Bills of Mortality and the Registrar General’s Weekly Returns from 1664 to 1930. Pictured, burials by cause for the week ending 26 September 1665, which was amid the Great Plague of London. Five deaths from ‘Flox and Small-pox’ are listed

Other events that the duo said may have impacted London’s smallpox outbreaks included conflict — including the Napoleonic and Franco-Prussian wars — as well as the Industrial Revolution, which brought urbanisation and demographic shifts.

‘Further research using mathematical models is needed to quantify the impacts of interventions and historical events on the smallpox outbreaks,’ Dr Krylova added.

The full findings of the study were published in the journal PLOS Biology.


  • The first known victim of smallpox was Pharaoh Ramses V of Egypt, who died in 1157BC and whose mummy still bears the scars of the disease.
  • When the Spanish took it into Hispaniola – now Haiti and the Dominican Republic – which they settled for sugar cane plantation in 1509, it killed every one of the 2.5 million natives within a decade.
  • More than 200 years ago, physician Edward Jenner made a crucial-discovery which led to the first vaccine. He found that milkmaids who developed cowpox through working close to the animals day after day seemed to be protected from smallpox, the human form of the disease.
  • In Britain, the disease was endemic until 1935.
  • The last major outbreak in Europe was in 1972 when 20 million were vaccinated after a pilgrim returning to Yugoslavia from Mecca infected 175 people.
  • Doctors waged a vaccination campaign to wipe out smallpox which succeeded by the late 1970s.
  • All nations were asked to destroy stocks of the virus or hand them to high-security installations in the US or Russia. It is feared terrorists may have got supplies from Russia in the 1980s.

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