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Vaccines: assessing the risks for world travellers

Carolyn Driver
RGN RM RHV
FPCert
MSc(TravelMed)
Independent Travel Health Specialist Nurse
Cheshire

While most patients who present for travel advice have usually come to "find out what jabs I need", it is important that the vaccinations themselves take up only a small part of the consultation. It is crucial that healthcare professionals realise that there is a lot more to a travel consultation than just the vaccinations. A full risk assessment should be performed that enables the adviser not only to determine which vaccines are required, but also to assess whether there are any other health risks that may require advice or prophylaxis (see Box 1).

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Primary vaccinations
The travel consultation is an ideal time to check that an individual has completed their primary course of vaccinations. If it seems likely that the full primary course has not been completed then a booster should be given - this should be with the combined tetanus, diphtheria and inactivated poliomyelitis vaccine (Revaxis; Aventis Pasteur MSD). If only one of the antigens is required it is still appropriate to use the combined vaccine.(1) For long-term travel to the more developing destinations, a booster of tetanus and diphtheria is recommended if it is more than 10 years since completion of the primary series. Poliomyelitis is still endemic in some African countries and in the Indian subcontinent, and travellers to these areas should also have their primary series boosted if it is more than 10 years since completion. As mentioned above, it is now appropriate to use Revaxis even if the individual is up to date for tetanus and diphtheria.

Hepatitis A
All travellers who venture outside of western Europe are recommended to have a hepatitis A vaccine. This food- and waterborne virus occurs throughout the world and can be acquired from water that the individual swims or bathes in, as well as through food or drink. It is the most commonly acquired vaccine-preventable infection in travellers.(2) The inactivated vaccines available in the UK are highly effective and can be used from one or two years of age onwards. There is now good evidence that two doses of the vaccine confer a minimum of 20 years' protection, and this may eventually prove to be lifelong.(3) The two doses should be given 6-12 months apart for complete protection, but there is no need to restart the course if a longer time than this elapses between the two doses.(3)

Other vaccines
All other currently available vaccines should be recommended following the risk assessment and consultation with appropriate up-to-date resources. Unless there is a compulsory requirement (which is rare), it should be the patient's choice as to whether or not they need the vaccines. The healthcare professional should facilitate this choice by providing information on the potential disease risk and the pros and cons of the vaccine. When helping a patient to decide, it is often the lifestyle they will adopt in their destination rather than the destination itself that is the most important factor, and the risk assessment should establish this.

Typhoid
Typhoid is a systemic infection caused by the Gram-negative bacillus Salmonella typhi and is transmitted by the faeco-oral and urine-oral route. While it occurs all over the world, the risk is greatest in areas where food and water hygiene are poor. In the UK most imported cases come from the Indian subcontinent.
Vaccination is recommended for all travellers to developing countries where food and water hygiene cannot be assured. Generally, travellers to the well-developed resorts will be at low risk, whereas those going to more "local" or remote areas, or those on a low budget, will be at higher risk.
The currently available vaccine is a pure polysaccharide antigen and confers short-term immunity for up to three years. This type of vaccine is not effective in very young children and gives, at best, 80% protection to older children and adults, so food and water precautions are still extremely important.

Cholera
Cholera is principally a waterborne infection but can occasionally be passed on through shellfish or other foods. Cholera is rare in travellers as a large infecting dose is required to cause illness. People who have great difficulty with clean water supplies, such as those living in very remote locations, especially those working in disaster areas or refugee camps, are most at risk. The oral cholera vaccine should be considered for these situations.

Hepatitis B virus (HBV)
HBV is the second most common vaccine-preventable disease among travellers.(2) The infection is caused by a bloodborne virus, and it is estimated that two billion individuals have been infected and that there are 350 million chronic carriers of the virus worldwide. Hepatitis B carriers have a high risk of developing cirr-hosis or carcinoma of the liver, and it is the second most common cause of cancer, surpassed only by smoking.(4)
HBV is transmitted by contact with blood or body fluids of an infected person in the same way as the HIV virus. The main difference between the two infections, however, is that HBV is 100 times more infectious than HIV. HBV has been known to remain infectious on environmental surfaces for at least a month at room temperature, and only 0.00004ml is required to transmit infection, making it highly infectious.
The world is divided into areas of low, intermediate and high prevalence of hepatitis B, and travellers from low endemicity can grossly underestimate their risk when travelling to areas of high prevalence (see Figure 1).

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Travellers can put themselves at risk of HBV infection through unprotected sex, tattooing, body piercing, acupuncture, sharing razors, toothbrushes or intravenous needles. Trauma is the most significant cause of morbidity in travellers and may require medical treatment in areas where instruments are not adequately sterilised or where blood is not screened. Dental treatment is another potential source of infection in developing countries. The risk of infection is more significant in those who travel to high-risk destinations for longer periods, and travellers indulging in risk-taking behaviour could easily become infected. Travellers should therefore be counselled about the mode of infection for hepatitis B and informed of the availability of a safe, effective vaccine.
There are two licensed hepatitis B vaccines available in the UK plus a combined hepatitis A and B vaccine. These are inactivated vaccines and can be used from birth (except Twinrix; GlaxoSmithKline vaccines) and should be administered intramuscularly into the deltoid muscle (or anterolateral aspect of the thigh in infants under 1 year of age). The original schedule of zero, one and six months is still the preferred regimen and should be used wherever time permits, but the accelerated schedules are useful for long-term travellers who have not allowed sufficient time. They need to be reminded, however, about the need for a fourth dose at 12 months. As both vaccines confer immunity in 96% of recipients who have completed a course, it is ­unnecessary to check for seroconversion in travellers, and they can be advised that boosters are unnecessary.(4)

Yellow fever
Yellow fever is a viral illness spread by the mosquito. The disease is endemic in sub-Saharan Africa and tropical South America. Symptoms vary from a mild flu-like illness to a fatal haemorrhagic fever. There is no treatment, and so prevention is very important.
A live-attenuated vaccine was developed more than 60 years ago that has proved to be safe and effective, conferring at least 10 years' protection after just one dose. The vaccine can be used from 9 months of age.
This is the only remaining vaccine for which there is a World Health Organization International Certificate of Vaccination, possession of which is mandatory for entry to some countries. Healthcare professionals need to ensure, however, that travellers are not misled by the assumption that if a certificate is not required at their destination then the vaccine cannot be important. If the disease occurs at their destination they should be advised to be vaccinated.
This is a live vaccine, so care should be taken with contraindications, especially in those with immune deficiencies. Although an exemption certificate can be given, the traveller should understand the risk they are taking by travelling to an endemic area without protection. Bite avoidance measures, such as covering up with light, loose, long-sleeved clothing and sleeping under a treated mosquito net, will be vitally important in this circumstance.

Rabies
Rabies is caused by a Lyssavirus occurring primarily in animals and leads to acute encephalomyelitis (inflammation of the brain and spinal cord), which is fatal once symptoms are present. The incubation period is on average three to eight weeks, but this can vary from nine days to many years. Worldwide there are an estimated 40,000-70,000 human deaths from rabies each year. The virus may be carried by any carnivorous animal, but dogs and cats (and occasionally bats) are the most likely to transmit the virus to humans. Rabies is present in all continents except Australasia and Antarctica. Developed countries have managed a high degree of control, so that the reservoir is primarily in the wild animal population, but in developing countries the dog is responsible for most of the human deaths that occur.
It is impossible to anticipate whether or not a traveller will encounter a rabid animal, and therefore they should be taught prevention measures (see Box 2).

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Postexposure rabies treatment is very successful if started promptly, but travellers who are going to be remote from major cities, or who will be travelling to developing countries where good postexposure treatment (including rabies-specific immunoglobulin) may not be available, should consider pre-exposure vaccination. This ensures that there are circulating antibodies already in the individual's system. Because of the extremely severe consequences of infection with rabies, it is always advisable to seek postexposure boosters after a bite. If, however, it takes some time to reach medical care, there will be an immediate booster response leading to high levels of circulating antibodies, and rabies-specific immunoglobulin will not be necessary.
The vaccine can be given from birth. Contraindications and side-effects to pre-exposure vaccines are similar to all inactivated vaccines. Generally it is a well-tolerated vaccination.
The usual schedule for pre-exposure vaccination is zero, seven and 21-28 days. Recipients should be reminded that in the event of a bite they should receive two further doses of vaccine - the first as soon as possible, and a second two days later.

Japanese encephalitis virus (JEV)
JEV is caused by a flavivirus, which is transmitted to humans by the Culex mosquito. The disease is endemic throughout South East Asia.
The reservoirs for the virus are domestic pigs and wading birds, and the areas of greatest risk tend to be rural farming communities. Various studies have been done to try to estimate the risk of transmission to tourists. It has been estimated that even in hyper-endemic areas the infection rate among mosquitoes does not exceed 3%, and the Centers for Disease Control in the USA estimated that the overall risk of JEV for short- term travellers was as low as 1 in 1,000,000.(5)
The travellers who are most likely to be at risk are those travelling to rural parts of South East Asia for long periods or those who will be living and working in an agricultural setting. Risk is highest during or just after the rainy season, when mosquitoes are breeding, and this should also be considered when performing a risk assessment.
Prevention relies on mosquito bite avoidance and, for those at significant risk, there are two unlicensed vaccines available in the UK, which can be given on a named-patient basis. These cannot be given under a Patient Group Direction, but doctors can write individual private prescriptions. The vaccines are available from either Sanofi Pasteur MSD or MASTA, and the schedules are three doses given at zero, seven and 28 days, with a booster at 2-3 years for those who will be at continued risk.
Contraindications are as for any inactivated vaccine, but atopic individuals and those who have severe reactions to insect bites have a higher incidence of allergic reactions to this vaccine.(5) Allergic reactions following vaccination can also be delayed, and there is a recommendation that the course is completed at least 10 days before departure from the UK so that appropriate treatment is available should this occur.

Tickborne encephalitis (TBE)
TBE is caused by a flavivirus, which is transmitted to humans by a tick. The infection occurs in parts of Scandinavia, central and eastern Europe and the western part of the former USSR. Transmission is mainly from April to August but may extend outside these months in unseasonably warm weather. Those at most risk of acquiring the infection are individuals working or camping in forested areas, or those on walking holidays who spend considerable time in wooded areas. Ticks brush off animals in the undergrowth and can then attach themselves to anything that subsequently brushes against the foliage.
Prevention involves appropriate protection from clothing and insect repellents, and FSME-Immun vaccine for those at significant risk (available from MASTA).
The schedule most commonly used for travellers is two doses intramuscularly given four weeks apart, and a booster can be given at 12 months for those with continued risk.
All those visiting endemic areas should be encouraged to inspect themselves for ticks after venturing into wooded areas. Medical advice should be sought if a tick is discovered, and immunoglobulin may be available for postexposure use.

Meningitis ACWY
Meningitis ACWY vaccine is compulsory for visitors to Saudi Arabia who will be attending either the Hajj or Umrah pilgrimages.
This vaccine is also recommended for certain ­travellers to the area made up of 18 African countries, known as the "meningitis belt", of sub-Saharan Africa. This is a disease of close association, and vaccination is recommended for those who will be living and working long term with the local population. It is not generally recommended for short-stay tourists; however, during major epidemics these recommendations may change, which is why it is important always to use up-to-date resources when advising travellers. Young people who have received the meningitis C vaccine in the UK would still need to be vaccinated with the quadrivalent ACWY vaccine if they are at risk, as the more predominant strains in Africa are A and W135.

Conclusion
Advising travellers on vaccine recommendations should be a two-way process, with the healthcare professional providing enough information to allow the individual to make their own choices as to which they wish to have. There are now ample sources of up-to-date information to support the adviser in this role. Most importantly, the traveller needs to be aware that vaccines prevent only a small proportion of travel-related ill-health, and time within the consultation should be given to advice on food and water precautions, as well as insect bite avoidance and other lifestyle risks.

References

  1. Department of Health. Immunisation against infectious disease. London: DH; 2004.
  2. Atkinson W, Wolfe C, Humiston S, Nelson R. Epidemiology and prevention of vaccine-­preventable diseases. 6th ed. Atlanta: CDC; 2000.
  3. Van Damme P, Banatvala J, Fay O, et al. Hepatitis A booster ­vaccination: is there a need? Lancet 2003;362:1065-71.
  4. European Consensus Group on Hepatitis B Immunity. Are booster ­immunisations needed for ­lifelong hepatitis B immunity? Lancet 2000;355:561-5.
  5. Plesner A, Ronne T, Wachmann H. Case-control study of allergic reactions to Japanese encephalitis vaccine. Vaccine 2000;18:1830-6.

Resources
National Travel Health Network and Centre Recent news and links to more detailed ­information sources
T:020 7380 9234
W:www.nathnac.org
Travax
Free to all in Scotland and Wales - £100 per year to practices in England or £500 per PCT
W:www.travax.nhs.uk
MASTA
Free to register as a professional but downloaded ­information may be charged
W:www.masta.org
Sanofi Pasteur MSD
Free to all ­healthcare ­professionals but requires registration
W:www.spmsd.co.uk
GlaxoSmithKline vaccines
W:www.vaccines.co.uk