Government policiy for travellers abroad appears to be a case of massive overkill. A handful of vaccines are urged and sometimes even forced on you anytime you venture much beyond our shores. If you were to listen to the UK Department of Health's recommendations "Health Advice for Travellers" or the Center for Disease Control and Prevention in the US, you'd get vaccinated against polio every time you stepped foot outside Europe, North America or Australia, even though the disease is virtually non existent in many of these recommended areas.The problem with this "just in case" mindset is not only that it creates a paranoic view of the world, but also that it offers travellers a false assurance that a simple jab can take the place of careful precaution when heading off to remote areas. Furthermore, it rests on the assumption that these jabs actually work. Of all the vaccines, travel vaccines have the poorest record of success. The old cholera vaccine has such a dismal track record that it may be one reason the World Health Organization (WHO) has dropped it from the list of required immunizations and no country requires it anymore.

With malaria there is not only no vaccine, but a dangerous and growing resistance to the drugs used to treat it.

With travel vaccines, more than any other, it's vital to find out how necessary, how safe and how effective each one is, even before you make your travel plans, particularly to less well trod areas. Here, in the first of two parts, are the available studies to date about malaria, cholera, typhoid and yellow fever.

Malaria

Of all infectious diseases abroad, malaria is perhaps your greatest risk. WHO estimates that there are 300-500m people infected with malaria, the parasitic disease carried by the Anopheles mosquito (JAMA, 1996; 275 (3): 230-233). Each year in Britain, 2000 people contract malaria and 12 people die, a higher figure than from any other tropical disease. (In America, where presumably fewer people travel to Asia and Africa, several hundred patients contract it every year.) There is no reliable vaccine for malaria, so the rationale has been that taking the drugs which treat malaria as prophylaxis (just in case measure) before, during and after your stay in the infected area will also somehow ward off the disease.

Several synthetic drugs developed during World War II to be taken against malaria used to be effective. The problem is that most strains of the disease have developed active resistance to the drugs. Few tropical countries are now unaffected by strains resistant to chloroquine, often used with proguanil (Paludrine), the former drugs of choice; resistance to quinine, an earlier favourite, is also now increasing. Consequently, doctors and even tropical vaccine experts are finding it difficult to tell patients which types of drugs work where any more. They tend to rely on a quick change scheme of swapping schedules of drugs frequently in the hope of outwitting resistant strains. The same applies to patients who return with malaria; the choice of treatment depends on the parasite's resistance to the drug in the area where you got the infection (New Eng J Med, 1996; 800-6).

The general rule of thumb at the moment is to use combinations of drugs in areas where resistance is known not to be high (BMJ,1993; 307: 1041; New Eng J of Med, 996; 335: 800-6).