Vaccination Priorities for Seafarers

Based on the text “Vaccination Priorities in Travel” by Robert Steffen MD (adapted for maritime environment by Nebojša Nikolić MD)

For today’s seafarers, ensuring that the correct immunizations are given prior to embarking is highly important, not only to reduce the personal risk of numerous vaccine preventable diseases (table I) but also to reduce the risk of the international spread of such diseases. Vaccine-preventable diseases are traditionally sub grouped according to those requested by national governments to fulfil entry criteria (e.g. yellow fever), those covered as part of routine immunizations based on national directives (e.g. poliomyelitis, diphtheria, tetanus, hepatitis B and measles), and those that are recommended based on the risk of acquiring infection whilst travelling (e.g. hepatitis A, rabies, typhoid fever and cholera). This risk very much depends on the location to be visited,[1, 2] along with the personal risk profile and duration of stay. Thus, unlike individuals travelling to developing areas, especially to remote regions and for prolonged periods who are at greater risk for acquiring infection, seafarers usually staying only few days in their cabins in ports, are less endangered. An epidemiological and host-related assessment of the intended trip should therefore be conducted when setting priorities for vaccination of seafarers and physicians need to be aware of which schedules can be both rapidly and effectively administered in order to provide some protection to last-minute embarking seafarers.

Vaccinations requested by national governments to fulfill entry criteria: Yellow fever

Yellow fever, an acute flavivirus infection, is transmitted by the mosquitoes Aedes

aegypti (urban yellow fever) and Haemagogus spp. (jungle, or sylvatic, yellow fever), but only occurs in tropical Africa and northern Latin America. Whilst extremely rare in seafarers today, it is a potentially fatal infection for which vaccination is highly recommended before entering an endemic area. Failure to comply with International Health Regulations can give rise to serious problems for the seafarers, such as refusal of entry to a country, requirement for vaccination at the airport upon arrival, and financial penalization, so all seafarers, as a rule, are vaccinated and must posses valid certificate in their “yellow books”. Every international port must have designated yellow fever vaccination center so if one’s certificate expires, seafarer can also be vaccinated in other than home ports.

Routine vaccinations: poliomyelitis, diphtheria, tetanus, hepatitis B and others

Poliomyelitis, diphtheria and tetanus are infections against which the World Health

Organization (WHO) and most national expert bodies consider vaccination to be routine because of their severity and clinical sequelae. Thus, relevant vaccinations are routinely administered during childhood in most industrialized countries, such that the incidence of these diseases is low in most areas of the world. This explains the absence of reports of travel associated tetanus or poliomyelitis in recent years, although it is still considered advisable to offer another once-only dose of poliomyelitis vaccine for those travelling to endemic areas.[2]

Seafarers are also advised to confirm that they have been fully immunized against diphtheria, especially in light of the diphtheria epidemic in the former Soviet Union between 1990 and1997 that resulted in fatalities among non-immune travellers.[3]

Hepatitis B is a viral disease associated with a wide spectrum of hepatic diseases, from a sub clinical carrier state to acute or chronic hepatitis, cirrhosis, and hepatic carcinoma. The incidence is 25 per 100 000 person-months of travel for symptomatic infections and 80 to 420 per 100 000 for all infections.[4] Studies suggest that an important minority of travellers either voluntarily break basic hygiene rules or inadvertently expose themselves to a risk of infection whilst abroad in high-risk countries.[5] Most often exposure to blood and bodily fluids, such as through casual sex, acupuncture, cosmetic surgery, tattoos or ear piercing were reported. The risk of infection is compounded by the fact that vaccination against hepatitis B is a relatively recent addition to routine childhood vaccinations in most industrialized countries, meaning that many of today’s adult seafarers are not yet protected against this infection. As such, hepatitis B is considered a ‘routine’ vaccination, but should equally be discussed under the section below concerning recommended vaccines. Such factors warrant careful consideration by healthcare professionals dealing with individuals intending to travel to hepatitis B endemic areas, such as Africa, Asia (except Japan and Singapore), Latin America (excluding Argentina and Chile), Eastern Europe and other remote countries. It is strongly advised that all maritime personal responsible for medical treatment of the crew is vaccinated against hepatitis B. considering their vulnerability for transmission of STI all seafarers should be recommended to vaccinate against hepatitis B.

Other infections for which routine childhood vaccinations generally occur in most industrialized countries include pertussis (whooping cough), Haemophilus influenzae type b, mumps, measles and rubella (German measles). Similarly, children in developed countries are often vaccinated against measles, although suboptimal compliance with vaccination (e.g. because of perceived safety concerns, particularly when combined with mumps and rubella vaccines) means that travellers may often be the cause of outbreaks on their destination continent.[6] Thus, it is important to ensure that the seafarer is fully immunized against the likes of poliomyelitis, diphtheria, tetanus, hepatitis B and measles because exposure to these diseases is possible in countries where vaccination uptake rates may vary.

Recent epidemics of measles on board cruise ships caused practice that all crewmembers must be vaccinated against mumps rubella and measles.

3. Recommended vaccinations: hepatitis A, rabies, typhoid fever and others

In order to determine the priority for recommended vaccinations it is useful to differentiate the various infections in terms of the risk of exposure. Such risk is greatest for hepatitis A (and to a lesser extent, rabies and typhoid fever) and lowest for the likes of cholera. Indeed, hepatitis A is the most frequent vaccine-preventable infection in non-immune individuals travelling to developing countries, with an average incidence of 300 per 100 000 person-months of travel. This rate may be as high as 2000 per 100 000 in groups such as longterm, low-budget backpackers and foreign-aid workers,[7] given the increased risk of exposure to potentially contaminated food and drink. Studies have also established that travellers to Asian and African regions bordering the Mediterranean, and the entire Caribbean, including those staying at luxury resorts, are at risk of infection. Such is the scale of the hepatitis A problem in developing countries, and its moderate disease severity, that most expert bodies recommend that every traveller receive hepatitis A vaccine prior to travelling to endemic areas. Especially seafarers working with sewage systems on board should be vaccinated. For those requiring concomitant protection against hepatitis B, as is often the case as the two diseases frequently co-exist in the same geographical area, a combination vaccine is available to offer convenient protection against both diseases with one vaccine.

Rabies is caused by a neurotropic virus transmitted to humans bitten by a rabid animal (most commonly dogs and bats). The risk of acquiring rabies is particularly high in Asia (excluding Japan), where 90% of all human deaths due to rabies occur,[8] along with Africa, Latin America and certain parts of Eastern Europe. Other geographical areas are rabies-free, e.g. Australia, New Zealand, the Pacific Islands, Scandinavia, the United Kingdom, Ireland, Iceland, Italy, France, and Switzerland. Rabies is of particular risk to those who are in close contact with local populations (and their domestic pets) over prolonged periods, such as missionaries and foreign-aid workers, along with those who travel by bike in high-risk areas, explore caves or otherwise work in a professional capacity with potentially rabid animals.[9]

Because of the impact of the infection, vaccination is therefore recommended for seafarers who are at high risk for being exposed to rabies during long stays in ports.

Typhoid fever, a potentially fatal disease caused by transmission of Salmonella typhi due to inadequate hygiene methods, has a monthly incidence rate of 30 per 100 000 among travellers to the Indian subcontinent, North and West Africa (except Tunisia), and Peru.

Elsewhere, the rate of typhoid fever is some 10-fold lower.[10–12] Expert panels therefore recommend that typhoid vaccine be administered to travellers who are at risk of exposure to S. typhi infection. Such risk groups include visitors to the aforementioned destinations, travellers to other destinations where their stay will be longer than 1 month, and those likely to be exposed to poor hygiene. Seafarers should be vaccinated if fall in one of those categories (long stay or poor hygiene). Meningococcal disease (an infection caused by Neisseria meningitidis) is rare in seafarers, even when staying in countries where the infection is highly endemic.[13] However, the infection can be lethal within hours of the first clinical signs and symptoms, with a mortality rate of around 20%. Whilst all travelers on Hajj or Umrah pilgrimages to Mecca need to be immunized by request of the Saudi government, most experts also recommend that all travellers to the African meningitis belt zone be vaccinated against this disease. It is important to note that such vaccination should provide coverage against as many disease causing serogroups as possible; i.e. serogroups A, C, W135 and Y (an effective vaccine for serogroup B is still at an experimental stage). This applies also to subjects who have already received meningococcal group C conjugate vaccine, which has become a component of the primary course of childhood vaccination in some industrialized countries.

Like yellow fever, Japanese encephalitis is a flavivirus transmitted by mosquitoes. A few dozen cases of this infection have been diagnosed in civilian travellers, seafarers among them within the past 25 years, which corresponds to an incidence rate of less than 1 per million given the number of travellers today.Subsequently, only those seafarers at risk of exposure to the infection whilst travelling should be vaccinated, i.e. seafarers sailing to known ‘risk’ areas (e.g. Southeast Asia) whose stay is going to be longer than 2 weeks in ports in deep in river estuaries.

Transmission of Mycobacterium tuberculosis during prolonged travel by air, rail or road has only rarely been reported. However, post-travel skin tests have established an incidence of infection of 3000 per 100 000 person-months of travel to areas of high endemicity; of those people with positive skin tests, only a very small proportion had active tuberculosis.[14] Subsequently, outdoor transmission of M. tuberculosis is considered negligible, with only long-term, low-budget travelers and expatriates being considered at higher risk because of repeated exposure.[15]

Special consideration to TB vaccination should be given to the crews on board cruise ships, due to the prolonged stay of large group of people in confines space and crew embarking from the countries where TB reappeared.

The risk of cholera, an acute infection caused by Vibrio cholerae, is approximately 0.2 per 100 000 travellers, although asymptomatic and oligosymptomatic infections may be more frequent.[16] Transmission occurs via the ingestion of food and drink contaminated by the excrement of individuals with symptomatic or asymptomatic infection. The case fatality rate among travellers is relatively low, at less than 2%. Subsequently, in view of its low impact

(i.e. low incidence and low risk of mortality), none of the expert groups currently recommend the vaccination of seafarers against cholera, although in some ports local port authorities are still asking for cholera-vaccination certificates.

Little is known about the risk of acquiring influenza during travel, although various outbreaks on cruise ships and after prolonged air travel have been described. The impact of the disease is greatest for those with risk factors such as increased age (³65 years) and preexisting disease (e.g. chronic respiratory or heart disease, and diabetes), all of those absent among seafarers. Subsequently, most organizations only recommend that ‘at-risk’ travellers be vaccinated against influenza prior to travelling. As the most frequent vaccine-preventable infection, however, some organizations are now considering whether to advise influenza vaccination for all travellers, irrespective of destination or season.

4. Prioritization of vaccinations

It is neither necessary nor justifiable for seafarers to receive all types of vaccines available. Rather, healthcare professionals must prioritize the vaccinations that are required based on the incidence and severity/mortality risk of various infections that the person may be exposed to during travel. This prioritizations process therefore dictates a consideration of numerous travel-, host-, and vaccine-related issues. Travel-related considerations include country of destination (including likely within-country destinations, i.e. city, resort, or rural area), duration and type of travel, as well as any legal immunization requirements at the destination. For example, travellers visiting rural areas (especially for prolonged periods and on a low budget) are more likely to be exposed to an infection risk than seafarers visiting only ports in urban areas.[1,2] Host-related considerations include personal immune status, state of health, age, and specific contraindications for vaccination. For example, it is pointless to vaccinate somebody against hepatitis A if they have already acquired lifelong immunity through prior infection with the disease. This is often apparent for seafarers from lower socioeconomic strata in developing countries, those with a history of jaundice.[4]

Vaccine-related considerations in the prioritization process include efficacy, safety, and cost. Indeed, vaccines for adult travelers are non-reimbursable under many national healthcare systems, meaning that financial constraints may preclude the seafarer from receiving all indicated vaccines.

We also have to consider the practice of last minute embarkations that became current practice in shipping industry, which has given rise to a large proportion of seafarers requesting vaccinations much later than the recommended 4 to 6 weeks prior to departure.

Such time constraints often make it impossible to administer the required multiple doses of a vaccine necessary to confer appropriate protection in office. In the case of hepatitis A vaccine, for example, many still believe that the vaccine does not protect if travel is imminent (i.e. within the following 2 weeks). Nevertheless, protection can still be offered through education and vaccination, even if this takes place on the day of departure. Indeed, studies show that as many as 79% of vaccines seroconvert within 13 days (see article in this supplement by Van Damme and Connor) and more than 99% of travellers achieve seroprotection at 1 month after the first dose of hepatitis A vaccine,[17] with only a few documented cases of hepatitis A among travellers who received an adequate dose.[7] Many believe that hepatitis A vaccine grants immediate protection, basing on post-exposure immunization success in primates and lack of vaccine failures with such practice. In the cases of last minute vaccinations, considering that seafarer can be vaccinated on board by the officer responsible for medical care of the crew, it is possible to vaccinate with the first dose and give the remaining doses of vaccine (accompanied by prescription) to the seafarer to take them on board and in appropriate time interval be vaccinated in the next port or on board.

5. Conclusions

From an epidemiological perspective, all seafarers should receive the required vaccines prior to embarking, as recommended by various expert bodies. The art of travel medicine, however, is not to give all available vaccines to travelers, resulting in unnecessary costs and risk of adverse events, but to prioritize these vaccines for the individual seafarer so that adequate protection is provided. The question, therefore, is to ascertain whether seafarers belong to groups at higher risk of infection, based on a thorough assessment of a variety of travel-, host-, and vaccine-related issues. In this setting time constraints are a crucial consideration, especially for the last-minute embarking seafarer.

References

1. Centers for Disease Control and Prevention. Health Information for International

Travel, 2001–2002. Atlanta, GA: US Department of Health and Human Services, 2001

2. WHO. International Travel and Health. WHO, Geneva 2003.

3. Galazka A. The changing epidemiology of diphtheria in the vaccine era. J Infect Dis

2000; 181 Suppl. 1: S2–9

4. Löscher T, Keystone JS, Steffen R. Vaccination of travelers against hepatitis A and B. J

Travel Med 1999; 6: 107–14

5. Zuckerman JN, Steffen R. Risks of hepatitis B in travelers as compared to immunization status. J Travel Med 2000; 7: 170–4

6. Rota JS, Rota PA, Redd SB, Redd SC, Pattamadilok S, Bellini WJ. Genetic analysis of measles viruses isolated in the United States, 1995–1996. J Infect Dis 1998; 177: 204–8

7. Steffen R, Kane MA, Shapiro CN, Billo N, Schoellhorn KJ, Van Damme P. Epidemiology and prevention of hepatitis A in travelers. JAMA 1994; 272: 885–9

8. World Health Organization. Rabies, Asia. Wkly Epidemiol Rec 2001; 76: 320–3

9. Haupt W. Rabies: risk of exposure and current trends in prevention of human cases.

Vaccine 1999; 17: 1742–9

10. Steffen R. Typhoid vaccine, for whom? Lancet 1982; 1: 615–16

11. Mermin JH, Townes JM, Gerber M, Dolan N, Mintz ED, Tauxe RV. Typhoid fever in the United States, 1985–1994: changing risks of international travel and increasing antimicrobial resistance. Arch Intern Med 1998; 158: 633–8

12. Caumes E, Ehya N, Nguyen J, Bricaire F. Typhoid and paratyphoid fever: a 10-year retrospective study of 41 cases in a Parisian hospital. J Travel Med 2001; 8: 293–7

13. Koch S, Steffen R. Meningococcal disease in travelers: vaccination recommendations. J

Travel Med 1994; 1: 4–7

14. Cobelens FG, van Deutekom H, Draayer-Jansen IW, Schepp-Beelen AC, van Gerven

PJ, van Kessel RP, et al. Risk of infection with Mycobacterium tuberculosis in travellers to areas of high tuberculosis endemicity. Lancet 2000; 356: 461–5

15. Rieder HL. Risk of travel-associated tuberculosis. Clin Infect Dis 2001; 33: 1393–6

16. Wittlinger F, Steffen R, Watanabe H, Handszuh H. Risk of cholera among western and Japanese travelers. J Travel Med 1995; 2: 154–8

17. Centers for Disease Control and Prevention. Prevention of hepatitis A through active or passive immunization: recommendations of the Advisory Committee on Immunization Practices. MMWR Morb Mortal Wkly Rep 1996; 45 (RR-15): 1–30

Table I. Vaccine-preventable diseases in travellers

Vaccinations requested by national governments (as an entry requirement)

• · Yellow fever
• · Menigococcal disease (for Hajj, Umrah)

Routine vaccinations

• · Diphtheria (Corynebacterium diphtheriae)
• · Hepatitis B
• · Measles
• · Poliomyelitis
• · Tetanus (Clostridium tetani)

Recommended vaccinations

• · Cholera (Vibrio cholerae)
• · Hepatitis A
• · Influenza
• · Japanese encephalitis
• · Meningococcal disease (serogroups A, C W135 and Y of Neisseria meningitidis)
• · Rabies
• · Tuberculosis (Mycobacterium tuberculosis)
• · Typhoid fever (Salmonella typhi)

Table II. Infections against which vaccination is recommended: environmental- and host-related risk factors

Infection Risk factors

Environmental Host (seafarer)

Cholera Work in refugee/aid agency camps

Gastric an acidity Hepatitis A Highly endemic in all developing countries

All travellers including seafarers especially those working on the sewage on board

Hepatitis B High prevalence in some countries

All seafarers, especially those designated to provide medical care on board

Influenza Prolonged travel by air, rail or road all travellers including seafarers

Japanese encephalitis Rural areas with stay > 2 weeks, especially in season seafarers on the ships touching ports in deep river estuaries in endemic areas

Meningococcal disease Epidemics, ‘meningitis belt’

(Sahel zone in Africa)

Close contact to locals

Rabies High endemicity (e.g. Asia) Young age, prolonged contact with local population, risk activity (e.g. bike travel, caving)

Tuberculosis Very remote areas Infants and children

Typhoid fever Recognised risk of exposure (e.g. travel to the Indian subcontinent, North and West

Africa [except Tunisia], and

Peru)

Gastric anacidity

Yellow fever Endemic region (tropical

Africa, northern South

America), mainly rural seafarers