Could a new vaccine, known as Dukoral, end our Delhi belly troubles while we're travelling?
They’ve had it in Sweden for a decade, and in Canada and Switzerland for a year or so now. Meanwhile, we Brits have been waiting with our buttocks clenched. Finally Dukoral – the new vaccine against travellers’ diarrhoea – arrived in Britain this spring. Does it mean no more rushing to some unfamiliar ‘smallest room’ wondering whether we’ll get there in time? Maybe.
The new ‘raspberry-flavoured’ vaccine has struggled to obtain the licence that allows it to be prescribed in Britain and, interestingly, British authorities have decided to restrict the vaccine’s use. To our friends in North America, ‘Dukoral helps stop diarrhoea before it starts’ and is promoted as a travellers’ diarrhoea preventative. To us in the UK, it is something completely different.
Moratoria are placed on drug companies until a product is launched so that even when I asked Dukoral’s manufacturers for information about their product they weren’t allowed to tell me about it. Finally, though, I was allowed to prescribe it but to my surprise I was told that this vaccine protected travellers against cholera only: in the UK Dukoral cannot be promoted as a vaccine against travellers’ diarrhoea. So even though the company knows that Dukoral has some protective effects, they are not allowed to claim that this is the case.
It is certainly quite effective against cholera: a big study in Bangladesh, tracking 89,596 people, showed that Dukoral gave 85% protection – certainly much more protective than the vaccine we used to stick into people, and which caused such a sore arm.
The problem for me as a travel-health advisor, however, is that although cholera is a huge killer in Bangladesh, it seldom harms ordinary travellers: the estimated risk of a first-world traveller becoming ill when exposed to cholera is one case in 500,000 journeys. As a comparison, the risk of catching hepatitis A is around one in 50.
The disastrous effects of cholera on people of the developing world – in particular in refugee camps – seems to feed off other health problems: those people may be marginally long-term malnourished and are also likely to be carrying other microbes which debilitate them and their immune systems. If travellers ask me, then, whether they should be immunised against cholera, I’d have to say, don’t bother – the risk of side effects of the vaccine is much higher than the benefit you’d derive.
I suspect that one of the reasons cholera is so misunderstood, has such a bad reputation and was so feared in the British Raj was that in those days of stool-gazing through not-very-clever microscopes, the cholera organism was easy to see as it hyperactively whizzed about under the lens. And because it was easy to see, all symptoms – whether caused by the cholera bug or by other filth-to-mouth microbes – would be blamed on cholera. This particular microbe has a worse reputation than it deserves.
In the West we don’t need a vaccine against cholera, so I looked again at the evidence of Dukoral’s protective efficacy against travellers’ diarrhoea. I was uneasy since, if expert committees had ruled it should not get the licence for travellers’ diarrhoea, surely we must assume that it does not protect? Not so. It gives around 65% protection against bog-standard enterotoxigenic E. coli – ETEC – the commonest cause of travellers’ diarrhoea.
This might sound good but, as vaccines go, this isn’t usually considered good enough, since this means that one-third of vaccinated people exposed to ETEC would be expected to get ill. But is that a real reflection on the vaccine’s performance in travellers? Jane Vincent Havelka, a Canada-based Wanderlust reader, reported: “I took Dukoral before departure on my trek in Himachal Pradesh in October – some of the British trekkers could have done with it! In five weeks in India, staying in budget hotels for the most part, I didn’t have one day of stomach problems. Not that this necessarily proves that Dukoral was the reason as I have a pretty stable stomach and I’m always super-careful with water. My excellent local travel clinic, with its highly knowledgeable staff, is promoting it.” She wanted to know whether I rated it too.
The problem in making a judgement about the vaccine is that it is difficult to study a disease entity that hits unpredictably. Decades ago, American medics got around this problem by feeding ‘volunteer’ prisoners known doses of dysentery-causing bacteria and then recording the symptoms afterwards!
American doctors have become a little more civilised lately; there are no more prison ‘volunteers’, so studies have to look at natural acquisition of disease. Then researchers have to sort out the difficult business of whether the vaccine truly protects or whether the lack of illness could be a chance effect. This is why the largest studies have been done in Bangladesh where the hit rate from all filth-to-mouth diseases is high.
The Bangladesh-based research showed that, although the protective effect against ordinary ETEC diarrhoea was unimpressive, it does give good protection against some of the more severe forms of diarrhoea. Most interestingly, and for reasons that are not yet understood, it also seems to protect against mixed infections of different diarrhoea-causing microbes including Shigella, which causes spectacular and severe bacillary dysentery.
Those travelling to diarrhoea and dysentery hot spots – the Indian subcontinent (especially during the current floods) and tropical Latin America – are exposed to such mixed infections and, for these people, this vaccine will be a welcome and effective defence. I’d recommend it.
I’d also emphasise, as our reader points out, that it is sensible to continue to be careful about what goes into your mouth. You don’t want to inadvertently swallow someone else’s poo. It is worth sticking to the ‘peel it, boil it, cook it or forget it’ rule.
Finally, remember that, however careful you are and whatever vaccines you take, travellers’ diarrhoea or dysentery can still strike, and it can be frightening. It is important for would-be travellers to know that drinking large quantities of clear fluids will correct such dehydration whatever the cause of the diarrhoea. Victims need to drink a couple of large (500ml) glassfuls of liquid after each visit to the long-drop, more if thirsty. This is rehabilitating – much more effective than swallowing Imodium or antibiotics – and will help most bouts to settle within 48 hours.
Dr Jane Wilson-Howarth works as a GP and in a travel clinic; this year she has taught on courses for practice nurses and others at the London School of Hygiene and Tropical Medicine at the Royal Free Hospital, and at the Homerton College of Nursing in Cambridge.
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