An outbreak of cholera commonly occurs in humanitarian disasters as with war in Yemen, where some 2000 people have died of cholera, or after the earthquake in Haiti. Usually vaccination begins after cases have occurred, but the sudden arrival of some 700 000 Rohingya in Bangladesh from August 2017, after being driven out by the Myanmar military, presented an opportunity to try and prevent an epidemic.

There was every reason to expect an epidemic: cholera is endemic in the Cox’s Bazar area of Bangladesh where the Rohingya arrived; when the Rohingya first arrived they were stranded in rain and mud without clean water and sanitation; it took time to provide shelter, water, and latrines; and even when established the camps remain crowded with water supplies restricted and contaminated.

Bangladesh is the home of icddr,b, which was formerly called the International Centre for Diarrhoeal Disease Research, Bangladesh and before that the Cholera Research Laboratory. (I’ve been the chair of the board for the past five years, but have just stepped down.) The Cholera Research Laboratory was set up in Bangladesh because the country had, and still has, endemic cholera. The centre has conducted many large scale trials of cholera vaccines and hopes eventually to persuade the Bangladesh government to introduce routine vaccination in the areas of Bangladesh known to have high rates of cholera. Cox’s Bazar, where the Rohingya camps are, is one of those areas.

It occurred to researchers at icddr,b that it could be possible to prevent a cholera epidemic in the Rohingya camps. In particular a comparatively recent trial led by Firdausi Qadri and her team had shown that a single dose of oral cholera vaccine rather than the usual two doses could reduce cholera infections in adults and children over 5 years-old; so giving the Rohingya an initial single dose might prevent an epidemic.

Some 700 000 Rohingya arrived over a short period of time starting in August 2017, and it was in September 2017 that the Director General of the Directorate General of Health Services in liaison with icddr,b contacted WHO in Geneva to see if it would release stockpiles of oral cholera vaccine. WHO agreed remarkably quickly, and within days some 900 000  doses arrived in Dhaka on a chartered flight. Qadri’s research had also shown that the vaccine remained effective, even without a tight cold chain, making operations easier.

Within a day of the vaccine arriving in Dhaka it was transferred to Cox’s Bazar along with 150 health workers from icddr,b used to mass vaccinations. In the most difficult conditions of rain and mud the workers managed to vaccinate 700 000 people in just a few more days. As I walked through the main camp on a sunny but relatively mild day more than a year later I marvelled at the logistical problems that must have arisen in simply ensuring that everybody was vaccinated. People were marked with ink to ensure that they weren’t vaccinated twice. Leaders of icddr,b and UNICEF had spoken to leaders of the Rohingya, and there was no resistance to being vaccinated. People understood the benefits, and, Qadri thinks, the fact that it was an oral rather than an injectable vaccine made the mass vaccination easier and more acceptable.

Although the trial of a single dose of the vaccine showed that it was not so effective in those aged one to five years old, they were vaccinated anyway—and then followed up later with a second dose. Indeed, most people have by now had a second dose, and some a third dose. Some local Bangladeshis living in close proximity to the Rohingya have also been vaccinated.

Nobody knew whether there was cholera in the area where the Rohingya came from or whether they had been vaccinated. It seemed unlikely that they had been vaccinated. Later studies showed that they had similar levels of immunity to cholera as Bangladeshis in Cox’s Bazar, which was lucky as that made it more likely that if they had no immunity then the vaccine would have been less effective.

It’s now more than a year since the mass vaccination, and there has been no outbreak of cholera among the Rohingya. icddr,b has set up surveillance sites in eleven health facilities, and uses a rapid test developed by icddr,b to test stool specimens and get an immediate result. Specimens are then sent to icddr,b’s labs in Dhaka for confirmation. So far there have been only the few cases you would expect in an endemic area.

This is the first time that mass vaccination has prevented a cholera outbreak rather than been a response to an outbreak. Of course an epidemic might not have occurred without the mass vaccination, but a professor of infectious disease told me he thought it “95% likely” that there would have been an epidemic. “We dodged a bullet,” says John Clemens, executive director of icddr,b and an expert on cholera vaccines.

The experience has important lessons for future humanitarian disasters, which sadly are bound to occur: pre-emptive vaccination can save lives.

See also: Visiting the camps of the Rohingya

Richard Smith was the editor of The BMJ until 2004.

Competing interest: RS has been the unpaid chair of the board of trustees of icddr,b for the past five years but has now stepped down. Icddr,b paid his expenses to travel to Dhaka for the board meeting and on to Cox’s Bazar to visit the Rohingya camps.