With the possible exception of quinine, for centuries the only treatment for malaria, and antibiotics, vaccines have saved more lives than any other intervention in medical history. Yet, from New York’s Brooklyn to Camden in north London to Kivu in the Democratic Republic of the Congo, vaccines are in retreat, shunned by populations who seemingly have little sense of the risks they are running with their own or other people’s lives.

Why this should be so is one of the conundrums of our age. Is it all the fault of social media and anti-vax propaganda that has taken root on Facebook, Twitter and YouTube? Or has society grown complacent about the risks that infectious diseases posed to previous generations, when it was common for children to be paralysed by polio or rendered deaf or brain-damaged by measles?

I will return to these questions, but first spare a thought for Kivu, in the northeastern DRC, where in the midst of what is officially the second largest Ebola outbreak in history, the rejection of vaccines is having particularly tragic consequences. Initially, it was hoped that the epidemic, which began last August, would follow the same pattern as a previous Ebola outbreak in the DRC, which was controlled by deploying a “ring vaccination” approach – vaccinating and monitoring a ring of people around each infected individual.

It was common for children to be paralysed by polio or rendered deaf or brain-damaged by measles

But that has not happened. Instead, in a region where one in four people is convinced that Ebola is “not real” and that the medical response is a scam by those in power to keep humanitarian aid flowing to the government, villagers have been hiding from World Health Organization contact tracers, while militias have been firebombing Ebola treatment centres, impeding the work of vaccination teams.

The result is that Ebola appears to be spreading under the radar and it is not known when the outbreak, which has already killed 751 people, might end. Most alarming of all, last Wednesday, the WHO reported 20 new cases of Ebola, the highest single day total of the outbreak. Two were workers at Butembo airport, a short plane ride from Kisangani, the DRC’s third largest city, with a population of 1.6 million. It is little wonder that the WHO held an emergency meeting on Friday to express its “grave concern” that the outbreak might be poised to follow the same pattern as the one that began in Guinea in 2014 and which eventually spread to five countries in west Africa and cost more than11,300 lives.

Given that Ebola is one of the most virulent pathogens known to medical science – “a molecular shark” in the words of the popular nonfiction writer Richard Preston – it is tempting to dismiss the resistance to vaccination in the DRC as a product of ignorance. After all, faced with a virus with a mortality rate of 60% that is burning out of control, refusing a potentially lifesaving vaccine is akin to a death wish.

New York mayor Bill de Blasio declares a public health emergency on 9 April in several postcodes after the city’s measles outbreak. Photograph: Erik Pendzich/Rex/Shutterstock

But it is not only in Africa that we have seen growing resistance to vaccination. So far this year, the United States, which eliminated measles in 2000, has seen 465 measles cases across 19 states. The majority have occurred in ultra-Orthodox Jewish neighbourhoods in Brooklyn and Rockland county, New York, where parents have shunned the measles, mumps and rubella vaccine, seemingly influenced by claims that the vaccine is not “kosher” because it contains “pig DNA”. In fact, the final product is highly purified and most rabbis accept that vaccines are not prohibited by religious laws.

It’s a similar picture in Europe, which recorded an astonishing 83,000 measles cases last year, triple the 2017 number, fuelled by similar anti-vax propaganda and British doctor Andrew Wakefield’s discredited theory purporting to show a link between the MMR jab and autism. Countless studies, the latest of which was published in the Annals of Internal Medicine in March, have shown the link is a fiction, but Wakefield’s theory continues to exert a pernicious influence, not least in Camden, north London, where it emerged last week that a third of five-year-olds have yet to receive the MMR jab. (Nationally, Britain’s MMR immunisation rate is 92%, the lowest for four years.)

Although it is difficult to gauge the impact of Facebook and Google on all this, the suspicion is that social media has skewed the game in favour of anti-vaxxers. But surely that is only part of the story. Ever since Edward Jenner lanced a milkmaid infected with cowpox and introduced the pustulent material into the arm of a healthy young boy in 1796, thereby inducing protection against the related smallpox virus, vaccination has proved a fertile ground for metaphorical fears. Hence the images of people sprouting cow heads in James Gillray’s 1802 engraving, The Cow-Pock.

What is surprising and demands more explanation is the persistence of these fears in the face of overwhelming scientific evidence that vaccination is a boon to health and, for the most part, safe.

Perhaps the phenomenon is best explained by our own hubris. With no experience of the childhood diseases that shortened or blighted our grandparents’ lives, much less tropical diseases such as Ebola and malaria, we have forgotten that it is only because of vaccines and other medical advances that we no longer need fear infectious disease. Instead, it is the remote and unproved risks of vaccines that keep us awake at night.

By contrast, the thought that keeps the WHO awake is that Ebola will escape the DRC and spark an international emergency. In 2014, the WHO was widely criticised for its complacency about the threat of Ebola in west Africa. It is because it is determined not to fall into the trap of hubris a second time that it is taking this epidemic so seriously.

• This article was amended on 18 April 2019. An earlier version said that Ebola “cost 11,300 lives”. This has been amended to state that it “cost more than 11,300 lives” to account for underreporting of deaths.

Mark Honigsbaum is a medical historian and the author of The Pandemic Century: One Hundred Years of Panic, Hysteria and Hubris