Over 200 years ago, Edward Jenner began the science of vaccinology (Association of the British Pharmaceutical Industry, 2002). Today it is used to offer protection against a variety of diseases. And, although there has been a fall in levels of routine childhood immunisation due to parental concerns over safety, numbers seeking travel immunisation continue to rise.
VOL: 98, ISSUE: 25, PAGE NO: 40
Terry Hainsworth, BSc, RGN, is practice nurse clinical lead, Judges Close Surgery, Mid Sussex Primary Care Trust
How do vaccines work?
When the body is infected by a disease it produces antibodies (proteins carried in the blood) which destroy the invading organism. The antibodies remember the disease-causing organism so that when next exposed they recognise and destroy it, so preventing a further attack.
Vaccines teach the immune system to produce antibodies without the body actually experiencing the disease. This is because vaccines contain disease-causing agents in a dead or weakened form so that they are unable to induce disease, and yet can stimulate the production of antibodies.
Recommending vaccines to the traveller
There are a variety of sources of information for travellers, such as journals, helplines and the internet. It is important to assess the amount of risk a traveller will be exposed to on their trip in order to select the appropriate vaccine. This involves consideration of the frequency and severity of local diseases, the amount of time the traveller will spend with the local population and the standard of hygiene they will be able to maintain. Experts do not always agree on the details of this risk assessment, which can result in some travellers receiving conflicting advice (Department of Health, 2001).
The following nine diseases can be prevented by the appropriate use of a vaccine. In order to practise immunisation safely, it is vital to have a knowledge of indications for immunisation, contraindications and adverse reactions connected with vaccines (Table 1).
This viral infection is acquired by the faecal-oral route. It is the most frequent vaccine-preventable disease that travellers contract, with 1,141 cases reported in 2001 (Public Health Laboratory Service, 2002). Symptoms include fever, malaise, nausea and abdominal discomfort, followed by the development of jaundice a few days later.
The illness normally lasts several weeks and recovery takes several months. In 2% of cases in people over the age of 40 and 4% of those over 60 the disease is fatal.
Travellers visiting developing countries are at significant risk of hepatitis A, with those exposed to poor conditions of hygiene at greatest risk (World Health Organization, 2002).
Immunisation must be offered free by GP surgeries (Department of Health, 1985). Several products are available, including combined hepatitis-A and hepatitis-B vaccines, or hepatitis-A and typhoid vaccines.
Typhoid is caused by consumption of Salmonella typhi in contaminated food or water. Important sources of infection include shellfish taken from sewage-polluted beds, fruit and vegetables fertilised by human waste (if eaten raw) and milk products. Flies are also able to transfer infection to food.
The symptoms include a gradual onset of fever, headache, malaise, intestinal upset, anorexia and insomnia. Untreated typhoid can be fatal and around 2-5% of those who contract typhoid fever become chronic carriers.
Travellers are usually only at risk when exposed to low standards of hygiene - except in parts of north and west Africa, south Asia and in Peru, where the risk is greater.
Immunisation against typhoid is commonly undertaken using the modern vipolysaccharide vaccine which, unlike the older whole-cell vaccine, causes only mild local side-effects and, rarely, systemic reactions.
Typhoid vaccination is usually available free from GP surgeries (Department of Health, 1985). There is a choice of product including a combined hepatitis-A and typhoid vaccine. In addition, an oral vaccine is available.
Yellow fever is caused by a viral infection transmitted by mosquitoes. Some infections are asymptomatic, but most lead to an acute two-phase illness, which in about 15% of cases develops into jaundice, abdominal pain, vomiting and haemorrhage and even death. Travellers are at risk in all areas where yellow fever is endemic, mainly in a band crossing central Africa and South America. The greatest risk is in jungles and forests. In some countries yellow-fever vaccination is mandatory for visitors who need to produce a certificate of vaccination (World Health Organization, 2002).
Immunisation can only be provided at registered yellow-fever immunisation centres. However, most travel clinics and many GP surgeries are registered and can provide a valid International Certification of Vaccination. Vaccination is not available free from the NHS. Supplies of yellow-fever vaccine have been restricted recently due to a problem with manufacture and some smaller centres have been unable to offer a service. However, supplies are starting to become more widely available again.
Hepatitis B is transmitted by infected body fluids, via person-to-person contact. Travellers need to be aware of the risk from sexual contact, contaminated blood products and needles and the potential risk of transmission through other skin-penetrating procedures such as tattooing. Many hepatitis-B infections only cause mild symptoms and may be difficult to spot.
Approximately 1% of cases are fatal and a proportion of adults develop a chronic infection, which can later develop into cirrhosis and/or liver cancer (World Health Organization, 2002). Travellers engaging in unprotected sex or working in health care projects are at risk and immunisation is recommended for this group and those planning a long stay (Department of Health, 2001).
A choice of product is available. Immunisation is not normally available free for travel purposes (Department of Health, 1986).
Tick-borne encephalitis is a mengingoencephalitis caused by a virus that is transferred through the bite of an infected tick. Although some degree of protection is afforded by clothing and applying insect repellant, travellers walking and camping in infested areas - mainly forested parts of Europe and Scandinavia - during the tick season are at risk and may require vaccination (World Health Organization, 2002). The vaccine is unlicensed in Britain but can be obtained by special request on a named-patient basis. Vaccination is not available free from the NHS.
Rabies is a viral infection that occurs following a bite from an infected animal, usually a dog. The disease consists of an acute viral encephalomyelitis, which is usually fatal. Rabies is present in animals in many countries, but most cases of human infection occur in developing countries. Travellers to a hyperendemic area, where the modern rabies vaccine may not be available, should consider pre-exposure vaccination (World Health Organization, 2002). Pre-exposure rabies vaccine is not available free from the NHS.
Meningococcal meningitis is caused by a bacterial infection spread by contact with infected persons or carriers. Most infections do not cause clinical disease but many infected people become asymptomatic carriers. Meningococcal meningitis has a sudden onset of intense headache, fever, nausea, vomiting, photophobia and neck stiffness. The disease is fatal in 5-10% of cases even with prompt treatment. The risk to travellers is considered low, but it increases for those who are staying in crowded conditions or taking part in large population movements such as pilgrimages.
Meningitis-C vaccination has been introduced into the childhood vaccine schedule, however Group-A meningitis is responsible for most infections abroad so travellers who are at risk should be offered the A and C vaccine. In addition a quadravalent vaccine with ‘Y’ and ‘W135’ strains is available for travellers to Saudi Arabia (Department of Health, 2001).
Free NHS vaccination for meningococcal meningitis is not available and travellers to Saudi Arabia may have to provide proof of vaccination.
Japanese encephalitis is a viral infection transmitted by mosquitoes that feed on infected pigs or birds. Most infections are asymptomatic but severe cases have a rapid onset and soon progress to high fever and meningeal symptoms. Approximately half of severe cases have a fatal outcome. The risk is low for most travellers, but visitors to rural and agricultural areas in endemic countries may be at risk and should consider immunisation (World Health Organization, 2002). Vaccination is not available free from the NHS and the vaccine is unlicensed in Britain.
This bacterial infection is contracted via the faecal-oral route, for which immunisation was at one time recommended. Most infections are asymptomatic but in severe cases there is a sudden onset of profuse watery diarrhoea with nausea and vomiting and rapid development of dehydration that can result in death due to circulatory collapse (World Health Organization, 2002).
The cholera vaccine that was used in Britain provided poor protection and has been discontinued. The risk to travellers is considered to be extremely small and prevention can be achieved through food and water hygiene (Department of Health, 2001).
In addition to providing the appropriate vaccines for travel, immunisations recommended for Britain should be kept up to date, especially tetanus. Details of contraindications, dose and side-effects must be confirmed with the manufacturer’s literature before administering any vaccination (Department of Health, 2001). It is important to seek informed consent before vaccination, following the Nursing and Midwifery Council’s code (2002), and to record travel consultations in full in line with UKCC guidelines (1996).
Travellers to several destinations or those, such as backpackers, whose activities increase their risk of infection, may require several immunisations. It is important to plan a schedule that allows time for missed appointments. However, many travellers book at short notice and this makes scheduling a challenge.
Travel vaccination can be complex but a methodical approach, drawing on a basic knowledge of diseases and vaccines, will lead to a good assessment of the traveller’s risks and appropriate, safe vaccination.