Assessing risk of travel

The Traveller and Vaccination- assessing the risks.

Dr Jonathan Klotnick (MBBCh-Wits)

 

The risk of acquiring illness during travel depends on the areas or locations the traveller will be visiting and the extent to which the traveller is likely to be exposed to diseases in that area. The precise risk for a specific disease in a specific area or location has been difficult to predict despite several decades of interest and investigation. To estimate the exact number of cases of a disease or infection in all travellers over a period of time at a location is very difficult to determine as many travellers will have returned to their home countries by the time the disease manifests. There are formulas and models that are used to predict disease risk, but disease risk is not stable over time and the data available  regarding the incidence of disease risk in travellers is based on extrapolation of limited data collected in limited samples of travellers anywhere from a few to more than 20 years ago1. . These studies have their strength and weaknesses and thus there are limitations of current epidemiologic knowledge.  

The pre-travel state of health of the traveller and his or her expected behavior whilst travelling are important considerations to acquiring disease. The travel health professional needs to prioritize with regard to the incidence and severity of the infections that may be encountered.

To assess risk, it is important to know “why” people are traveling. Is it for business, leisure, to fulfill personal hobbies, for professional activities and it is also important to determine the duration of stay, environmental hazards, possible exposure to diseases and  the behavior patterns of the travellers- conservative or ‘risk takers’.

The hygienic standard at the point of the travellers destination is the more important point to consider than whether the traveller is going to be in a rural or urban area2. . For example: if two people were travelling and one was going  to a rural area  and the conditions are more hygienic than the other staying in a poorly kept place in an urban area, the fact that rural area is cleaner and more hygienic than the urban, the urban traveller would require more vaccine protection than the rural traveller. Tourists and business people with high standards of living are less likely to be exposed to disease than high risk travellers such as students who back-pack and stay at inexpensive places.

 



 The duration of travel is important because the risk of infection increases with time. A person staying one night in a Central African Republic capital city has much less of a chance of acquiring infection than someone staying for more than 2 weeks at the same place.

Another risk to consider is a cumulative risk of travel. If a business man stays in a very good and hygienic hotel for one night at a time in a relatively high risk country for disease, if he frequents the country with many trips his cumulative risk of acquiring disease becomes much higher. Thus a once off one night stay and never to return to the country with a relatively high risk has a much lower cumulative risk.

With regard to vaccine risk, travellers may elect to be vaccinated prior to travel to protect themselves from vaccines-associated diseases. In doing so, they protect themselves and this will, to a certain degree, protect others from the spread of these diseases (herd effect).3.4. The rationale for vaccination is based on the fact that vaccine preventable diseases occur throughout the world and some are more common than.5. A basic concept to remember when assessing the traveller is that common diseases happen commonly and that rarer diseases remain rare. Outbreaks of rare diseases still occur and due to media hype, public misinformation etc. travellers often request vaccinations for the rare diseases and the common vaccine preventable diseases are felt by them to be less important.

The fact that global travel is rising there is most certainly an increased risk of exposure to infectious diseases, some of which are vaccine preventable. There are many travel vaccines available and not all travellers require these vaccines. It is ultimately up to the travel practitioner to assess the risks associated with the trip the traveller is about to embark on and vaccinate accordingly. It is essential to weigh up the vaccine risk to the traveller and the associated health risks at the destination/s of travel.  It is not good medicine practice to vaccinate travellers against rare diseases that have a low case-fatality rate when treated effectively. It is also poor practice to leave travellers unprotected against more frequent and life-threatening infections for which no effective treatments are available. An example of this is the meningococcal meningitis vaccination. Although the incidence rate of meningococcal meningitis is low in travellers, 0.4 cases per 100 000, in the case of The Hajj, which takes place in Saudi Arabia, the incidence rates are 200 cases per 100 000.6. Muslim pilgrims have been exposed to meningococcal meningitis and are exposed to influenza. The authorities by instituting that pilgrims require the meningococcal vaccine and highly recommend the flu vaccine, the number of cases of meningococcal meningitis and flu has reduced substantially.

We often assume that routine childhood vaccinations have been administered and thus travellers have received the full immunization series against Diphtheria, Polio, Pertussis, Measles and Hepatitis B in childhood. Even if this is not the case travellers should be given catch up vaccinations. Exposure to these diseases is possible in countries where coverage rates for these vaccinations are not as high as coverage rates in industrialized countries.

The only compulsory travel vaccine is Yellow Fever, when travelling to Yellow Fever endemic areas. All travellers are compelled by international travel law to have the vaccine when visiting or transiting through the Yellow Fever countries. (Exceptions and exemptions do exist to receiving this vaccination, however this is discussed in other chapters of this book and will not be discussed here).

All other vaccinations are recommended and are not compulsory.

Some of the recommended travel vaccines in order of likely exposure risks from high risk to low risk will be discussed briefly.

The risk of vaccine preventable diseases can be categorized as follows:

High risk- influenza and hepatitis A.

Intermediate risk- Hepatitis B, Typhoid (North Africa and India), Measles, Rabies (asses risk exposure)

Low risk - other vaccines such as Cholera, Meningitis, Yellow Fever, Tetanus, Diphtheria, Polio, Japanese Encephalitis. Pertussis, although considered low risk, has recently emerged in countries such as Australia and Europe. Thus low risk vaccine preventable diseases many at times move to intermediate risk for periods of time but still revert back to low risk with time.

The most frequent vaccine preventable infection in non immune individuals travelling to developed and developing countries is influenza. All travel practitioners should recommend this vaccination as a priority above other recommended vaccines, particularly at the start or peaks of the influenza seasons in the different hemispheres. Influenza vaccines should be given to travellers in all age groups.

The second most frequent vaccine preventable disease in non immune travellers travelling to developing countries is hepatitis A.7.

In travellers to Africa this should be at the top of the recommendation list. This disease has also been a recent concern in certain developed countries in Europe. Budget restricted travellers are at high risk of acquiring hepatitis A, however even luxury or high end travellers can still be exposed, though to a lesser degree.

The fact that respiratory diseases are common in the middle aged to elderly travel patients (age 65 and older), the flu vaccine and pneumococcal vaccine should be priorities in this group of travellers.8.9. It is also very important to remember that immunity to vaccines acquired previously may have waned and it is very worthwhile to vaccinate this group of travelers with the four-in-one Tetanus-Diphtheria-acellular Pertussis-Polio vaccine. One third of Tetanus cases occur over the age of 60 and with the re-emergence of Pertussis, this vaccine is highly recommended in this age group.

In younger adult travellers and teenagers, consideration should be given to hepatitis A and B, influenza, MMR and Tetanus-Diptheria-acellular Pertussis-Polio vaccines. Students at universities and staying in dormitories or student residents should be candidates for meningococcal meningitis vaccinations. Younger adults of childbearing age should receive a rubella vaccination and a varicella vaccination if there is no history of the disease and no known prior vaccination. They should ideally check for immunity to the two diseases prior to conceiving.

The age of 50 is an appropriate time to review preventative health measures, especially vaccinations. More than one third of persons aged 50-64 have risk factors that are indications for pneumonia immunization, and many need tetanus boosters.


Other special travel risk patient groups include the following: 10.

·         Pregnancy- live viral vaccines are contraindicated in pregnancy such as MMR, varicella and oral polio. Yellow Fever although contraindicated may be administered if the risk of acquiring Yellow Fever is high. Breastfeeding is not a contraindication for vaccines.

 

·         Immunosuppressed travellers- live viral vaccines are contraindicated in patients with congenital immunodeficiencies, HIV positive patients with CD4 counts less than 200, active leukemia, lymphoma, generalized malignancies, immunosuppressant therapy and supraphysiological doses of cortisone. Inactivated vaccines can be safely administered but their effects may be suboptimal.

 

 

·         Haemophilia and bleeding disorders travellers- many tolerate IM injections and firm pressure should be applied to the site of vaccination.

 

·         Travellers with liver disease are at risk of developing complications from many vaccine preventable diseases. This group should be considered for hepatitis A&B, pneumococcal, influenza, tetanus, MMR and varicella vaccines.

 

·         Travellers with splenic dysfunction or asplenic travellers should receive the pneumococcal, meningococcal meningitis and haemophilus influenza vaccines due to the risk of acquiring fatal disease.

 

·         Travellers who are health care workers or public safety workers should consider hepatitis B, influenza and MMR vaccines. Food handlers need to have hepatitis A vaccines and animal handlers need to have rabies vaccines as priorities.

Some travellers may argue against vaccination for travel.11. Those who argue against may do so usually due to the following factors: cost of the vaccines, potential for adverse effects of the vaccine, concerns of reports of adverse events which are often lacking in evidence or are exaggerated, and by misinformation and ignorance of travel agents, friends, internet, or travel practitioners who are not up to date.

In today’s challenging economic environment, the cost of the vaccine and the possible adverse reactions need to be considered and explained to the traveller prior to immunization. Vaccine safety gets more public attention than vaccination effectiveness. Today vaccines have an excellent safety record.12. There have been many falsely reported adverse vaccine reactions, so negative aspects of vaccination are publicized more than the positive aspects of vaccination. As a result of misguided vaccine safety concerns, vaccine coverage in many countries has fallen resulting in the re-emergence of diseases such as measles and Pertussis.13.

We as travel health practitioners are responsible to provide up to date recommendations about which vaccines should be administered for travel, but the final decision whether to accept or refuse the vaccination lies with the traveller.14. We can only educate the traveller with regards to the risks involved with travel and the hygienic and safe practices that should be adhered to, but we cannot enforce it.

 

References:

1) Leder K, Wilson ME, Freedman DO, Torresi J. A comparative analysis of methodological approaches used for estimating risk in travel medicine. J Travel Med. 2008 Jul-Aug; 15(4):263-72

2) Steffen R, Connor BA. Vaccines in travel health: from risk assessment to priorities. J Travel Med 2005; 12: 26-35

3) Berger A. how does herd immunity work. BMJ 1999; 319: 1466-7

4) John TJ, Samuel R. Herd immunity and herd effect: new insights and definitions. Eur J Epidemiol 2000; 16: 601-6

5) Plotkin SL, Plotkin SA. A short history of vaccination. In: Plotkin SA, Orenstein WA, eds. Vaccines, 4th edition. Philadelphia: WB Saunders; 2004:1-15

6) Koch S, Steffen R. Meningococcal disease in travellers: vaccination recommendations. J Travel Med 1994; 1:4-7

7)Muntsch M, Spicher VM, Gut C, Steffen R. Hepatitis A virus infections in travellers, 1998-2004. Clin Infect Dis. 2006 Feb 15; 42(4):490-7

8)Freedman DO, Weld LH, Kozarsky PE, Fisk T, Robins R, von Sonnenburg F, et al. Spectrum of disease and relation to place of exposure among ill returned travellers. N Engl J Med. 2006 Jan 12; 354(2):119-130.

9)Christenson B, Hedlund J, Lundbergh P, Ortqvist A. Additive preventive effect of influenza and pneumococcal vaccines in elderly persons. Eur Respir J 2004; 23: 363-8

10) Succi RC, Farhat CK. Vaccination in special situations. J Paediatr (Rio J) 2006; 82: S91-100

11) MacIntyre CR, Leask J. Immunization myths and realities: responding to arguments against immunization. J Paediatr Child Health 2003; 39:487-91

12) Folb PI, Bernastowska E, Chen R, Clemens J, Dadoo AN, Ellenberg SS, et al. A global perspective on vaccine safety and public health: the Global Advisory Committee on vaccine safety. Am J Public health 2004; 94: 1926-31

13) Atkinson P, Cullinan C, Jones J, Fraser G, Maguire H. Large outbreak of measles in London: reversal of health inequalities. Arch Dis Child 2005; 90:424-5

14) Steffen R, Amitirigala I, Mutsch M. Health risks among travellers-need for regular updates. J Travel Med. 2008 May-Jun; 15(3):145-6