All the best-laid travel plans will unravel if you should fall ill during the trip. It’s best to be prepared as best you can.

IN 2004, worldwide travel exceeded 750 million international arrivals, and it is estimated that there will be more than one billion travellers per year before 2015, with South and East Asia, the Middle East and Eastern Europe identified as the most rapidly growing tourist areas1.

In Europe alone, between 1990 and 1995, the number of long-haul trips increased by 11 million, with long-haul journeys representing an estimated 20% of all European travel by the year 20002.

Hepatitis A, hepatitis B and typhoid fever are amongst the most widespread vaccine-preventable diseases throughout the world. It is estimated that over one million people die every year from hepatitis B-related illnesses.

According to the World Health Organization (WHO), 1.4 million new cases of hepatitis A and about 16 million cases of typhoid fever occur globally each year. However, since the reporting of these two infections is known to be incomplete, the true incidence is thought to be as much as 10 times higher3,4,5.

Risk of infection for travellers

The risk of infection increases with duration of travel and low levels of hygiene, which is why backpackers are at highest risk. In fact, the monthly incidence rate for unprotected persons in any developing country varies between three and 2,000 per 100,000 with the lower figure applying to tourists and business persons staying in good hotels.

The higher figure applies to persons staying in accommodation with a lower standard of hygiene.

Fortunately, the risk of transmission between passengers in an aircraft is no different from close encounters on trains, buses or at the cinema. That means transmission of infection may occur between passengers via coughing, sneezing and direct contact of inanimate objects like furnishing, newspapers and magazines.

However, highly infectious diseases like influenza may spread when the ventilation system is not operating. This occurs on occasions when the aircraft is on the ground, due to environmental or technical reasons.

It is important to note that when the ventilation system is working, the risk of transmission of any infection is very low due to the highly effective recycling and filtration process of the cabin air.

Aircraft disinfection is in fact a public health measure mandated by the International Health Regulations.

Major vaccine-preventable diseases and the best prevention strategy

Infections most often acquired by travellers are traveller’s diarrhoea – most commonly due to Escherichia coli, and upper respiratory tract infections, including influenza.

Most diarrhoeal diseases are not vaccine-preventable, but other food or water borne infections that are vaccine preventable include hepatitis A, typhoid and poliomyelitis.

In contrast, a number of respiratory infections are vaccine-preventable and they include influenza, pertussis, diphtheria and measles.

The art of travel medicine however, is not to give all available vaccines but to make the correct decision according to how far down the priority list is the recommended protection6.

It is certainly inadvisable to protect a traveller against rare and less serious infections, while leaving him or her at risk of more frequent and serious ones.

Multiple vaccinations

Travellers would clearly benefit from the administration of a combined vaccine against diseases with overlapping endemicity and risk factors (for example, hepatitis A and B, or hepatitis A and typhoid).

The schedule for combined vaccination often has a number of advantages over the respective monovalent vaccines. Fewer injections are involved, which means fewer visits to the healthcare provider, and therefore, greater convenience to both the vaccinee and healthcare provider7.

In addition, a schedule with fewer injections encourages higher compliance due to improved comfort.

Bock and colleagues investigated the potential influence of hepatitis A vaccination on the immune response to other travellers vaccines administered concurrently8.

Volunteers received a hepatitis A vaccine, and together with a vaccine against polio, hepatitis B, diphtheria, tetanus, yellow fever, Japanese encephalitis, typhoid fever or rabies. The results demonstrated that there was no negative effect of concurrent traveller vaccinations on the immune response to the hepatitis A vaccine.

Similarly, concurrent administration of a hepatitis A vaccine did not result in impairment of the antibody response to these other travel vaccines.

The feasibility of administering a combined hepatitis A and B vaccine together with a monovalent Vi polysaccharide typhoid vaccine either by extemporaneous syringe mixing or concomitant separate injection has also been assessed9.

The two vaccination regimens were found to be equivalent in terms of immunogenicity, with more than 96% of subjects in both groups seropositive for anti-HAV and anti-Vi within one month. At month seven, 99% of subjects in both groups were seroprotected against hepatitis B.

Duration of protection

Data has shown that following successful primary vaccination against hepatitis A, protective antibody levels persist beyond 12 years in healthy individuals and underlying immune memory provides protection far beyond the duration of detectable anti-HAV antibodies-10.

The group concluded that there is no evidence to support HAV booster vaccination following successful primary vaccination in a healthy individual.

The protective efficacy of a primary course of hepatitis B vaccine is also well established. However, until recently there was no consensus on the need for booster vaccination to sustain protection.

In 1998, a panel of European experts met to review the need for hepatitis B booster vaccinations11. They concluded that long-term protection against hepatitis B depends on immunological memory, which allows a protective anamnestic antibody response to antigen challenge that lasts for at least 15 years in healthy individuals.

To date there are no data to support the need for hepatitis B booster doses in healthy individuals who have responded to a full primary course.

A single dose of typhoid vaccine however, provides immunity against typhoid fever for only three years. Thus, WHO and ACIP both recommend that individuals who remain at risk of typhoid fever should be revaccinated every three years using a single dose of Vi polysaccharide vaccine12,13.

How flexible is the vaccination schedule?

One may begin considering vaccination around four to six weeks before departure. While it is acceptable to lengthen the time interval between doses, significant shortening of the intervals is not recommended.

According to general recommendations, primary HAV vaccination should be administered following a two-dose schedule, with the second dose administered six to 12 months after the first.

However, due to the constraints of an imminent departure, many travellers do not complete the two-dose primary HAV vaccination schedule. While one dose of hepatitis A vaccine will provide protection for up to one year post-vaccination, studies have also shown that a delay in the timing of the second dose, of up to 72 months after the first dose, does not appear to affect the subsequent immune response14,15.

However, until the efficacy of one dose has been established, it is important to stress the need for full primary vaccination, preferably within the recommended period (i.e. the second dose should be administered six to12 months after the first), to ensure a robust anamnestic response and long-term protection.

Solutions for last-minute travellers

An imminent departure date is often seen by travellers as a deterrent to immunisation, given that most vaccines need to be administered at least two weeks before departure.

However, although a late vaccination may not offer immediate protection against infection, for long duration trips, it is probably better to be vaccinated late as opposed to not at all.

Additional protection

One should always be constantly aware that vaccines do not fully protect 100% of the recipients. Additional precautions should be followed to help reduce the risk of acquiring diseases, especially for those in which no vaccine exists.

These precautions include the use of insect repellents, pre-exposure prophylactic treatment and ensuring safe drinking water and food. Always remember to COOK IT, BOIL IT, PEEL IT OR FORGET IT.

References:

15. Iwarson S, Lindh M, Widerstrom L. Excellent booster response 4–6 y after a single primary dose of an inactivated hepatitis A vaccine. Scand J Infect Dis 2002; 34: 110–1.

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