Immunization is not enough / by John Clements

Immunization is not enough Vaccines are amongst the greatest gifts to mankind from medical science. Not only can protection of the individ- ual be achieved, but control of some diseases and eradication of others become possible . Today the traveller can benefit from a large number of vaccines. However, not all are necessary , and their efficacy and side-effects vary considerably. There is a danger that , because they have received a vaccine against one particular disease , trav- ellers may assume they are immune to all similar infections. In reality , immunization must go hand in hand with safe health behaviour if dis- eases are to be avoided during tra- vel-which puts much of the onus for health on the traveller himself. Take the cholera vaccine , for ex- ample. We are now in the seventh pandemic which began in 1961 and has so far affected 92 countries. In bygone times , cholera shadowed Islamic pilgrims from the Far East on their way west to Mecca. Ships returning to Europe from Arabia were kept anchored off shore for 40 days in "quarantine " (the Ital- ian word for 40 is " quaranta ") ; the principle was that anyone harbour- ing the cholera organism would be either dead or better in that time. The advent of the vaccine using the killed organism raised hopes that cholera would be ousted as a cause of fatal diarrhoea. However, cholera basically at- tacks the lining of the gut so any effective vaccine must provide pro- tection at the mucosal level (the layer of lining cells) within the gut itself. This poses problems , since vaccines are usually given by injec- tion, a route which does not pro- duce immunity at the mucosal lev- el. Such a vaccine has had only modest effect in volunteer studies and limited effect in field trials. Ad- ditionally it was apparent that the vaccine was not preventing trans- mission of the disease or asymp- W oRLD HEALTH. December 1987 by John Clements tomatic infection. This is why the need for a valid cholera vaccination certificate was withdrawn as a re- quirement for international travel. One preliminary study of an oral cholera vaccine using non-living subunits of the organism gave around 70 per cent protection against infection. On the other hand, it looks as if an injectable vaccine containing a live form of the organism which has been atten- uated may provide nearly 90 per cent protection- but with an unac- ceptably high rate of adverse reac- tions such as diarrhoea . But some individuals may consider that , de- spite the limited protection provid- ed by the vaccine and the very low risk of travellers actually contract- ing the disease , it may be worth being immunized if a long time is to be spent in a genuine cholera endemic area. Vaccines against typhoid fever have been administered for many years and have a much better track record, producing between 65 and 70 per cent protection. But they need to be given by injection and are of limited acceptability because of a high incidence of reaction which may prostrate the recipient. Again , research has come up with some promising new vaccines which are given orally. In contrast to cholera , there is little doubt that typhoid vaccine is effective and that the risk of infection for travel- lers is not trivial. Travellers who are given one or both of the cholera and typhoid vaccines may develop immunity and be protected from developing the diseases . But they are far from safe from the scores of other food- and water-borne diseases contract- ed in the same way as cholera and typhoid . The only way a traveller can protect himself (or herself) against all of them is by paying fas- tidious attention to what he drinks and eats. Only chlorinated water sources afford significant protection against viral and bacterial water- borne diseases. Even chlorine , at the levels used in routine disinfec- tion of water, does not kill the cysts of Giardia Iamblia and Entamoeba histolytica, the organisms respon- sible for giardiasis and amoebiasis respectively . In areas where chlori- nated water is not available and where hygiene and sanitation are poor, only the following may be safe to drink : - Hot beverages, such as tea and coffee , made with boiled water. - Canned or bottled carbonated beverages , including carbonated bottled water and soft drinks. - Beer and wine. Where water is contaminated, ice must also be considered suspect , and may in turn contaminate con- tainers used for drinking unless the containers have been thoroughly cleaned with soap and hot water af- ter the ice has been discarded . Ice cream may also be a source of in- fection . It is safer to drink directly from a can or bottle of a beverage than from a questionable container. Water on the outside of cans or bot- tles of beverages , as well as ice , may be contaminated. So wet cans or bottles should be dried before being opened , and surfaces which come in direct contact with the 21 Immunization is not enough mouth when drinking should first be wiped clean. If no other source of safe drinking water is available, tap water that is uncomfortably hot to the touch is usually safe and, af- ter being allowed to cool at room temperature in a clean container, can be used for brushing teeth as well as for drinking. But boiled water is obviously preferable. Food should be selected with care to avoid illness. In areas of the world where hygiene and sanitation 22 are poor, it is best to avoid unpas- teurised milk and milk products, such as cheese, and to eat only what can be peeled or has been thoroughly cooked and is still hot. Cooked food served after it has cooled may be loaded with bacteria and should be avoided. It is advisable to avoid uncooked salad vegetables in developing countries, as they are sometimes fertilised with human faeces. This often results in contamination with amoebic cysts, parasite ova or pathogenic bacteria. Uncooked meats and fish should be avoided, as many helminth (parasitic worm) infestations are transmitted in this way. Uncooked or incompletely cooked shellfish may carry typhoid, cholera, polio- virus, hepatitis and Vibrio para- haemolyticus. Diseases spread by insects are dealt with elsewhere in this issue. The most effective form of preven- tion against all insect-born diseases is to take steps not to be bitten by an insect carrying the disease. Children as travellers are a special case. Being up-to-date with immunization according to the re- commended schedule at home is important, but may not be enough, particularly in the first few months of life. Although all the required shots may have been given, full im- munity may only develop after doses not yet administered. If chil- dren are to mix with local children Above: Pilgrims' tents near Mecca in Saudi Arabia. Prevention of diarrhoea! diseases is vital in such circumstances. Left: "A court for King Cholera ": this cartoon from the English weekly Punch in the 1850s acknowledges that insani- tary conditions played a part in spread- ing disease. Photos WHO W oRLD HEALTH, December 1987 during travel (and who can prevent them?) , they are likely to be at greater risk of exposure to the six main childhood diseases normally included in childhood immuniz- ation programmes, in particular po- lio and measles. If children are nine months of age or more at the time of travel and not yet immunized, they should be given measles vac- cine , regardless of the recommend- ed schedule at home. Nine months seems to be the earliest age when most maternal antibodies have dis- appeared from the child's body, and the vaccine is likely to be pro- tective . If possible at least three doses of oral polio vaccine should have been given and at least three doses of diphtheria-pertussis- tetanus (DPT). The BCG vaccine against tuberculosis should be given on a discretionary basis after dis- cussion with a physician. Good protection is now available against two forms of hepatitis . For 40 years gamma globulin has been recommended as protection against hepatitis A. The globulin is collect- ed and pooled from donors known to have had the disease. This form of immunization is known as pas- sive protection because the recipi- ent uses someone else's defence system and generates no antibodies of his own. Protection soon after the injection is of the order of 80 or 90 per cent but falls off rapidly with time . Additional injections are needed in order to maintain immu- nity , and all too many travellers ne- glect to arrange for the appropriate repeat doses. For most travellers , hepatitis B does not pose a major risk as infec- tion generally comes from close physical contact. But those who put themselves at risk from job-related infection or infection from occa- sional sexual encounters (be they homosexual or heterosexual) may obtain protection with either the first generation plasma-derived vac- cines or the newer second genera- tion recombinant DNA vaccine. Both give excellent levels of protec- tion. However, the sexually adven- turous may be lulled into a false sense of security, not realising that no protection has been provided against AIDS and a variety of other sexually transmitted diseases. The condom is the nearest thing to a panacea in such circumstances, but no one is quite sure how good it W oRLD HEALTH , December 1987 really is. However stuffy and out- of-date it sounds, sexual abstinence seems to be catching on. The best news for travellers is the development of vaccines against yellow fever and meningococcal in- fection. Providing the right type of vaccine has been given, protection against meningococcal meningitis is in the order of 90 per cent. How- Vaccination Certificate Requirements and Health Advice for International Travel Vaccines available * Cholera (only recommended when required by an ind ividual country) * Yellow fever **Polio ** Diphtheria ** BCG (against TB) **Measles ** Tetanus ** Pertussis Typhoid Gamma globulin (against hepatit is A) Hepat itis B Influenza Rabies Meningitis Anthrax Plague Japanese Encephalitis * Disease subject to the Internat ional Health Regulations for which vaccination may be required. **The six vaccines recommended in chi ld- hood by WHO for inclusion in the Expanded Programme on Immunization. ever, not too many travellers need this. The "cerebrospinal meningitis (CSM) belt" extends through the semi-arid region south of the Saha- ra, where meningitis is hyperende- mic with periodic epidemic waves at 10- to 15-year intervals. Other re- cent epidemics have centered in Nepal and Delhi. Because the or- ganism is spread easily in confined spaces (historically, army recruits in cramped sleeping accommo- Immunization is not enough dation caught it), visitors sleeping in crowded quarters may be at risk. But the vaccine has to be of the right serogroup. Most epidemics involve types A and C, and good vaccines are available for these . One shot of yellow fever vaccine will provide excellent protection for at least ten years, and severe reac- tions are extremely rare -less than once every million shots. Anyone contemplating a trip to countries near the yellow fever belts of Africa and South America would be fool- ish not to be immunized (unless they are pregnant) , given that the fatality rate in travellers can be as high as 50 per cent. Countries with yellow fever are identified in " Vac- cination certificate requirements and health advice for international travel ," published annually by WHO. If the place to be visited is in the throes of an influenza epidemic, the traveller would be well advised to be immunized. But the influenza virus leads scientists a merry dance and always seems to be one step ahead. The virus continually changes itself as it travels round the globe , and advice even from the most up-to-date source may recom- mend immunization against a strain of virus that has already been superseded by another. Visitors to countries where rabies is endemic should not normally require the vaccine. The best advice is to stay away from dogs. Some feel it necessary to be immunized because they will be at special risk -people such as veterinarians, agri- cultural advisors or laboratory workers. The human diploid cell rabies vaccine is the vaccine of choice because of its efficacy and freedom from complications and ease of administration. However, individuals who receive pre-expo- sure immunization should not as- sume they are immune ; there is a slight risk that they may not have formed sufficient antibodies to the vaccine, so anyone bitten should seek professional advice, whether or not they have had the vaccine. Although there are still problems and pitfalls associated with the use of vaccines for travellers, there is no doubt that the individual can re- ceive a high level of protection against certain diseases. One final point however : immunization will only be effective if it is accompa- nied by safe health behaviour. • 23