The Black Death: what was it, how did it start and what effect has it had?

It's a disease we associate with medieval times, when it was known as the "Black Death", but fears are growing that an outbreak of bubonic plague could be the next global pandemic.

With that fear in mind, scientists behind the Oxford/AstraZeneca Covid jab are working on a vaccine that could give immunity against the disease, which has killed more than 200 million people across the world throughout history.

While Britain has been plague-free for several centuries, there have been recent small outbreaks in other parts of the world, last summer, the WHO added the bacteria that causes the illness to its pathogen prioritisation watchlist of potential pandemic triggers.

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At present, cases of bubonic plague can be treated with antibiotics, but worries about the potential emergence of an antibiotic-resistant strain of the Black Death superbug has led to calls for the UK to find a vaccine to add to its stockpile, said The Telegraph. Trials of the newly developed vaccine on healthy adults began in 2021, and results have now shown it to be safe and able to produce an immune response. Professor Andrew Pollard, director of the Oxford Vaccine Group, who is leading the study, told The Telegraph that the results will be submitted to a journal for peer review "within weeks", and further clinical trials will take place.

Bubonic plague does continue to infect and kill people today, particularly in rural parts of Africa, Asia and America. There are even about seven cases in the US each year, although only 14 deaths were recorded between 2000 and 2020. "The risk of contracting bubonic plague in the UK is currently very low," Professor Pollard told The Telegraph.

As well as potentially saving lives, the development of the vaccine also "addresses broader challenges of managing re-emerging infectious diseases in a world increasingly interconnected by trade and travel", Select Science said.

What was the Black Death?

The Black Death, caused by the spread of the yersinia pestis bacteria by rats, was a devastating pandemic that first struck Europe in the mid-1300s, when it's estimated to have killed up to two-thirds of the population. Its name is a "reference to the gangrenous blackening and death of body parts, such as the fingers and toes, that can happen with the illness", said the BBC.

There are three different types of plague: bubonic, pneumonic and septicaemic. "If left untreated, the bubonic form has a 30 percent to 60 percent fatality rate and the pneumonic form is almost always fatal. Both bubonic and pneumonic plague can develop into a life-threatening infection of the blood called septicaemia," said an Oxford University briefing for the Oxford Vaccine Group.

Where did it come from?

A popular theory was that the Black Death originated in China, but "an international team of researchers now believes" that the 14th-century pandemic "began in Kyrgyzstan", wrote Clive Cookson, science editor at the Financial Times, in 2022. "Some tombs near Lake Issyk-Kul are inscribed with the word 'pestilence' in the Turkic language."

The researchers analysed DNA from human remains in two cemeteries in the Tian Shan region that saw a surge of burials in 1338 and 1339. Lead author Maria Spyrou, from the University of Tübingen, said: "We found that the ancient strains from Kyrgyzstan are positioned exactly at the node of this massive diversification event. In other words, we found the Black Death's source strain and we even know its exact date: 1338."

Her study also suggested the Black Death was originally spread from fleas on marmots and then moved into fleas on rats and then to humans through fleabites.

The "buck-toothed and fluffy" marmot might seem relatively harmless but "it could have been to blame for killing half of Europe", said The Telegraph.

The plague, seeded in what is now northern Kyrgyzstan, is thought to have jumped into a community of Christian traders "who then spread the disease via the Silk Road".

It arrived on the British Isles in 1348, travelling on boat from the then English (now French) province of Gascony, and the speed with which it spread has led scientists from Public Health England's Porton Down science labs to argue that it began to spread by air, making "its way into the lungs through coughs and sneezes", said History.

Between 1346 and 1353, the plague destroyed a higher proportion of the population than any other single known event. "The living were scarcely sufficient to bury the dead," said History Extra.

How did it end?

Most theories suggest that it was the imposition of quarantine measures that ensured the end of the Black Death. People would remain in their homes and only leave when it was necessary, to avoid becoming infected, while wealthier individuals would leave densely populated areas to live in greater isolation.

Improvements in personal hygiene are also thought to have played a part, alongside the introduction of cremations rather than burials, due to the sheer number of bodies.

In subsequent years, further plague epidemics hit the UK, with the worst outbreak since the Black Death beginning in 1665, when London lost around 15% of its population. It's commonly believed that it was finally wiped out by the Great Fire of London in 1066 – a good story, but sadly not true, said the London Museum. In reality, the number of deaths had been in decline before the fire, and continued after it. "We're still unsure why the plague did not return to our shores after it faded out in the 1670s, but it wasn’t due to London’s terrible fire," the museum's site said.

What is the Black Death's legacy?

"A historical turning point, as well as a vast human tragedy, the Black Death of 1346-53 is unparalleled in human history," said Ole J. Benedictow at History Today.

It would take 200 years before Europe alone was able to replenish its population to pre-plague numbers, while the world also suffered monumental setbacks in terms of labour, art, culture and the economy.

There is also an argument that some people today are susceptible to certain diseases because of DNA passed down the generation by plague survivors, said Fortune in 2022, citing a study that found that "genetic variants identified as protective against the plague are associated with Crohn's disease, rheumatoid arthritis and lupus".

However, in 2024, a team from the University of Cambridge said their own studies of skeletal DNA from people living before and after the plague in Cambridgeshire could find no "substantial evidence that the Black Death has shaped the genetic make-up of surviving individuals", said scientific news site Technology Networks.

Where is the Black Death found today?

With the exception of Oceania, plague can still be found on all continents as an animal disease, and there continues to be a risk that it can transfer to humans, reported the WHO.

While epidemics have occurred in Asia and South America, most human cases since the 1990s have been in Africa. The three most endemic countries are the Democratic Republic of Congo, Peru and Madagascar, where cases of bubonic plague are reported nearly every year.