Although only a small minority of travel-related illnesses are caused by vaccine-preventable diseases, vaccination still has an important part to play in protecting travellers. The fact that a disease may be present in a country does not necessarily imply that all travellers to that country are at risk, and a thorough risk assessment for each traveller is needed, taking into account such factors as the time of year, length of stay, specific areas of the country to be visited and activities to be undertaken.
Backpackers and low budget travellers are likely to be at higher risk than other travellers, and all travellers should be encouraged to attend at least six weeks prior to departure to ensure completion of multi-dose schedules. Immunocompromised patients, be it from HIV, medication or whatever cause, may not achieve full protection, and live vaccines such as yellow fever may be contraindicated.
Up-to-date information on indications, contraindications, dosage schedules and duration of protection is available from the sources listed in Box 1.
Some general guidelines for commonly used travel vaccines
All travellers should ensure that they have the following vaccinations:
- UK schedule vaccinations should be up to date
- Influenza vaccine: especially for older travellers and those with chronic respiratory problems
- Hepatitis A vaccine: for travellers to resource-poor countries where food and water hygiene are a problem
- Typhoid vaccine: for similar countries, especially in South Asia.
Some less commonly used travel vaccines:
- Hepatitis B vaccine: for travellers such as volunteers, health care and aid workers, and for those at risk from sexual transmission
- Meningococcal ACWY vaccine: particularly for travellers living or working in close proximity to local residents, especially in sub-Saharan Africa
- Yellow fever vaccine: for travellers to specific risk areas of Africa and South America. Available only at registered yellow fever vaccination centres. A certificate of vaccination is valid only from 10 days after vaccination. Protection from one dose is now considered to be lifelong. Older travellers are more prone to serious adverse effects
- Rabies vaccine: for travellers working with animals or at high risk of contact with animals, or travelling in remote rural locations, especially relevant in South and Southeast Asia
- Japanese encephalitis vaccine: particularly for long stay travellers to rural areas in South and Southeast Asia, especially in the rainy season
- Tick-borne encephalitis vaccine: for travellers to high-risk areas of central and eastern Europe and Scandinavia undertaking outdoor activities
- Cholera vaccine: possibly for aid workers in refugee camps but not for most travellers.
In the last 20 years there have been between 1,500 and 2,000 cases of malaria imported into the UK, with between three and 16 deaths, though in recent years the numbers have been steadily falling. The majority have occurred in travellers coming or returning from Africa, and the larger proportion of these have been due to the more serious Plasmodium falciparum species. All travellers to malaria-endemic countries should be advised to follow the ABCD of malaria prophylaxis:
- Awareness of risk
- Mosquito Bite precautions
- Chemoprophylaxis with an appropriate drug
- Prompt Diagnosis of fever during or after travel.
For travellers to areas with relatively low transmission rates, an alternative to chemoprophylaxis may be to carry emergency standby treatment to be taken in the event of fever occurring.
Detailed information on malaria prevention in UK travellers is available in the UK Malaria Guidelines (available at https://www.gov.uk/government/publications/malaria-prevention-guidelines-fortravellers-from-the-uk) and from the information sources in Box 1, which give valuable information on the levels of risk from country to country.
While there is some risk of malaria throughout the tropical world, the highest levels of risk occur in Africa, especially in West Africa. Although any traveller to an area of high malaria transmission is at risk, so-called VFR (visiting friends and relatives) travellers – those of immigrant origin returning to their country of origin to visit friends or relatives – have a disproportionally high risk of importing malaria on their return. They may consider themselves immune, but the partial immunity, acquired from repeated exposure to infection, is greatly reduced within months of residence in the UK. This group of travellers presents a great challenge to travel health advisers, firstly, in encouraging them to seek pre-travel advice, and, secondly, in persuading them of the necessity to take precautions, including antimalarial drugs.
Anopheles mosquitoes, the vector of malaria, are night-time biters, the risk of transmission occurring between dusk and dawn. The following precautions should be advised, particularly at those times, though similar precautions should be taken during the day to avoid daytime-biting mosquitoes that transmit other infections such as dengue.
- Cover up as much of the skin surface as possible with loose-fitting, preferably light-coloured clothing, as mosquitoes are attracted to darker colours
- Apply insect repellent to exposed skin, the most effective containing diethyl toluamide (DEET)
- Ensure that doors and windows are mosquito-proof
- Sleep under a bed net
- Spray knock-down insecticide into the room before retiring to bed.
Table 1 lists antimalarial drugs advised for prophylaxis in UK travellers. For more information consult the UK Malaria Guidelines or any of the sources in Box 1.
Some current travel health issues
Thanks to a high-profile outbreak in Brazil, zika gained a large amount of publicity in the news media, but virtually all other South American countries have reported cases. Most of Central America and the Caribbean islands have also been involved, though the incidence is now reported to be falling. Zika has also been reported widely in sub-Saharan Africa and the Indian subcontinent and there have been cases in Texas and Florida.
Zika virus is transmitted by Aedes species mosquito (Ae. aegypti and Ae. albopictus), which lay eggs in standing water in small containers such as oil drums, tin cans and old tyres. They bite mainly during the day, but they can also bite at night. Zika can also be transmitted from mother to child during pregnancy and by sexual contact for some months after infection, and the use of condoms should be advised.
Zika virus infection is not usually a particularly severe illness of itself, with symptoms including fever, rash, headache, joint pains, conjunctivitis and muscle pain, but it can be a cause of Guillain-Barre syndrome and infection of the foetus can produce microcephaly. The significance of zika for travellers is, therefore, mainly for women who are pregnant or for women or their partners who are contemplating a pregnancy.
There is not a specific treatment for the virus, but vaccines are currently undergoing trials. Travellers to any of these areas should be advised to take precautions against mosquito bites throughout the day (see advice regarding bite precautions earlier in this article).
For those with symptoms suggestive of zika returning from an infected area, both blood and urine tests are available. See https://www.gov.uk/guidance/zika-virus-sample-testing-advice for more information on what tests should be used and at what time following onset of symptoms.
Chikungunya is a viral infection transmitted by the same species of mosquitoes that transmit zika. Its symptoms include fever, severe joint pains, muscle pains, headache, nausea, fatigue and rash.
The disease was originally found mainly in Africa, Asia and the Indian subcontinent, but it is now present throughout most of South America and the Caribbean, Central America, the USA and southern Europe.
There is no specific treatment, and mosquito bite avoidance is the only preventive measure available to UK travellers, though a vaccine has recently been developed in the USA. Blood tests such as viral culture, viral RNA and antibodies are available depending on the stage of the illness. For more information on testing visit https://www.cdc.gov/chikungunya/hc/diagnostic.html.
Dengue is also a viral infection transmitted by the same species of mosquitoes as zika and chikungunya. Dengue is found in parts of Southeast Asia, the Caribbean, the Indian subcontinent, South and Central America, Africa, the Pacific Islands and Australia.
ts symptoms include fever, which can reach 40°C or higher, severe headache, pain behind the eyes, muscle and joint pain – sometimes so severe it has meant dengue has been nicknamed “break-bone fever”, nausea and vomiting, a widespread rash and loss of appetite, but a majority of infections are subclinical. More severe life-threatening manifestations of dengue – dengue shock syndrome and dengue haemorrhagic fever – occur in a minority of cases.
These complications are relatively rare in travellers, and occur mainly in local populations. There are four distinct strains of dengue virus, and severe dengue is thought to be caused by a hyper-immune reaction when an individual, previously infected with one strain, becomes infected with a different strain. Again, there is no specific treatment, and mosquito bite avoidance is the only preventive measure.
A vaccine has recently been developed and has been recommended by the World Health Organization only for residents aged between nine and 45 years in countries with a high disease burden, and is, therefore, unlikely to be recommended for travellers. Virus, PCR and antibody testing are all available, depending on the stage of the illness. For more information visit
http://www.gponline.com/recognising-dengue-feverclinical-features-diagnosis-treatment/infections-and-infestations/immunisation/article/1295268 for more information on testing.
Mike Townend MB ChB (Hons), Dip Trav Med, FFTM RCPS (Glasg), Hon Fellow BGTHA
Hon Clinical Senior Lecturer, University of Glasgow & Past Chairman, British Global and Travel Health Association