Public health
Travel-Associated Viral Infections: an Overview
Last reviewed 2 July 2026
International travel connects every country to every reservoir of viral disease on the planet, and it does so well within the incubation period of almost every human virus. A traveller can acquire an infection in a high-transmission setting, cross several borders while still well, and become unwell or infectious only after arriving somewhere with little local immunity and little clinical familiarity with the disease. Travel medicine works on both halves of that problem at once: reducing what the individual traveller is exposed to, and reducing what a traveller can seed on return.
Two clinical encounters carry most of the viral work. The pre-travel consultation is preventive and is organised around vaccines and behavioural advice matched to the itinerary. The assessment of the returning traveller is diagnostic and is organised around geography, exposures and the incubation period, with the overriding early task of separating the benign and self-limiting from the rapidly dangerous.
The pre-travel risk assessment
No single vaccination schedule suits every traveller, because risk is a product of the person and the trip together. The consultation is ideally held four to eight weeks before departure, which leaves time to complete multi-dose courses and for protective immunity to develop, since most primary doses take about 7 to 10 days to protect. A traveller seen the day before a flight can still be helped, but the options narrow sharply.
The assessment weighs the destination and the specific itinerary rather than the country alone: an air-conditioned city hotel and a rural rice-farming district in the same country carry very different risks, and altitude and season modify both (yellow fever transmission, for example, falls away above roughly 2,300 metres, and influenza tracks opposite seasons in the two hemispheres). It weighs the duration of travel, the planned activities (safari and freshwater contact, cave exposure, healthcare or laboratory work, sexual contact, adventure sports), the style of accommodation, and the traveller’s own health: age, pregnancy, immune status, chronic disease, allergies and prior vaccination all shift both the risk and the choice of vaccine. Entry requirements imposed by the destination complete the picture.
Vaccines are never fully protective and cover only a fraction of travel-associated infection, so the consultation pairs them with the advice that does the rest: avoiding mosquito and tick bites, safe food and water, hand hygiene, safer sex, and animal-bite avoidance. The same visit reviews and catches up the traveller’s routine national immunisations, which is often where the largest real risk (such as measles) is quietly closed. The traveller should leave with a written record of what was given.
The three categories of travel vaccine
Travel vaccines fall into three groups by the reason they are given, and the distinction matters clinically and legally.
Routine vaccines are the ones already in a country’s national immunisation programme. The pre-travel visit is an opportunity to confirm the traveller is up to date and to catch up anything missed, because travel often takes a person from a well-vaccinated setting into one where a childhood disease still circulates freely. Recommended vaccines protect against diseases endemic at the destination; the aim is to protect the traveller and to reduce the chance of importation on return. Required vaccines are demanded by certain countries as a condition of entry, and proof must be shown on an international certificate. Only three diseases sit in this last group worldwide: yellow fever, polio and meningococcal disease, and of these only yellow fever is a routine entry requirement rather than a situation-specific one.
A second distinction cuts across all three groups and governs who may safely be vaccinated: whether the vaccine is live or non-live. A live attenuated vaccine replicates in the recipient, which produces strong, durable immunity but makes it unsafe in pregnancy and significant immunocompromise; a non-live vaccine cannot replicate and is safe in those groups but often needs boosters. Yellow fever, measles-mumps-rubella, varicella, oral polio, rotavirus and the live attenuated dengue and influenza vaccines are live; hepatitis A, hepatitis B, inactivated polio, Japanese encephalitis, tick-borne encephalitis and rabies vaccines are not.
The vaccines a traveller may need, and the category each falls in:
| Vaccine | Viral or non-viral | Category | Vaccine type |
|---|---|---|---|
| Yellow fever | Viral | Required and recommended | Live attenuated (17D) |
| Poliomyelitis | Viral | Required (some countries) and routine | Inactivated (IPV); live (OPV) elsewhere |
| Meningococcal ACWY | Non-viral | Required (hajj and umrah) | Conjugate or polysaccharide |
| Hepatitis A | Viral | Recommended | Inactivated |
| Hepatitis B | Viral | Recommended and routine | Recombinant subunit |
| Japanese encephalitis | Viral | Recommended | Inactivated (Vero-cell) |
| Tick-borne encephalitis | Viral | Recommended | Inactivated |
| Rabies | Viral | Recommended (pre-exposure) | Inactivated |
| Hepatitis E | Viral | Recommended (licensed in China only) | Recombinant |
| Cholera | Non-viral | Recommended | Killed oral |
| Typhoid | Non-viral | Recommended | Conjugate, live oral or inactivated |
| Dengue | Viral | Endemic residents, not general travellers | Live attenuated tetravalent |
| Measles, mumps, rubella | Viral | Routine | Live (MMR) |
| Influenza | Viral | Routine | Inactivated, recombinant or live |
| Varicella and zoster | Viral | Routine | Live (varicella); recombinant (zoster) |
| Rotavirus | Viral | Routine | Live oral |
| Human papillomavirus | Viral | Routine | Recombinant (virus-like particle) |
Required vaccines and the International Health Regulations
The authority to demand a vaccine as a condition of crossing a border comes from the International Health Regulations (2005), a legally binding instrument that almost every country has adopted. The regulations let a country require proof of vaccination for a defined set of diseases, recorded on the International Certificate of Vaccination or Prophylaxis, the document travellers know as the yellow card.
Yellow fever is the only viral vaccine required under international law. A country may demand the certificate from travellers arriving from a country where yellow fever transmission occurs, and the requirement can apply even to airport transit. The purpose is not only to protect the individual: many countries that have never had yellow fever are nonetheless receptive to it, because they carry competent Aedes mosquitoes and susceptible primate hosts, and a single imported viraemic traveller could establish local transmission. The certificate becomes valid 10 days after vaccination. Since the regulations were amended on 11 July 2016, a single dose is accepted as giving lifelong protection, and the certificate is valid for the life of the person; a booster can no longer be required for entry. Where the vaccine is genuinely contraindicated, a clinician’s medical exemption letter takes the place of the certificate. The list of countries with a requirement or a transmission risk is revised continually, and no requirement at a destination does not mean no risk there. The Eliminate Yellow Fever Epidemics (EYE) Strategy, a coalition running from 2017 to 2026, coordinates the mass preventive vaccination that underpins this system in endemic Africa and the Americas.
Polio requirements arise from a separate mechanism. The international spread of poliovirus has been a Public Health Emergency of International Concern since 2014, a status reaffirmed at each review, most recently in March 2026, and it carries temporary recommendations. Travellers staying longer than four weeks in a country with wild or vaccine-derived poliovirus circulation may be required to show proof of a polio dose received between four weeks and twelve months before departure, again documented on the certificate. Wild poliovirus type 1 now remains endemic in only two countries, Afghanistan and Pakistan, but vaccine-derived strains circulate more widely and the list of affected countries changes, so the current position must be checked at the time of travel.
Meningococcal vaccination, though non-viral, completes the required group: Saudi Arabia requires proof of quadrivalent (ACWY) meningococcal vaccination from pilgrims arriving for the hajj and umrah. The certificate itself is a legal document, and the requirements sit in international law that each country, including South Africa, gives domestic effect. This is the practical face of the medico-legal dimension of travel medicine: the clinician who signs a yellow card is completing a document with force in international law.
Vaccine-preventable viral infections of the traveller
The viral diseases a vaccine can prevent divide naturally by how they are acquired: the arboviral infections spread by insect bite, the enteric and bloodborne infections tied to food, water and contact, and the respiratory and close-contact infections. Each agent below has a full profile in the virus atlas; what follows is the traveller-facing summary of who is at risk and what the vaccine offers.
Arboviral infections with a vaccine
Yellow fever is endemic in tropical sub-Saharan Africa and tropical South America, where it cycles between forest primates and mosquitoes and spills into humans on the forest edge or, more dangerously, into urban outbreaks carried by Aedes aegypti. A single dose of the live attenuated 17D vaccine gives lasting protection and is recommended for anyone from about nine months of age travelling to a risk area. The trade-off is safety in specific groups: the vaccine is contraindicated in significant immunocompromise, including symptomatic HIV or a CD4 count under 200, and is given only with caution in pregnancy, in infants aged six to eight months, and in travellers aged 60 and over, in whom the rare but serious vaccine-associated neurological and viscerotropic reactions are more common and occur almost only after a first dose.
Japanese encephalitis is the leading cause of vaccine-preventable encephalitis across Asia and the western Pacific, maintained in a cycle between wading birds, amplifying pigs and Culex mosquitoes that breed in flooded rice fields. The risk to most travellers is very low, but it rises toward the local rate with long or rural stays in the transmission season, and the disease is untreatable and often fatal or disabling. The inactivated Vero-cell vaccine, given as a two-dose course with an accelerated option for adults, is recommended for travellers spending a month or more in endemic rural areas, for frequent travellers, and for shorter trips with heavy rural or outdoor exposure. Recent range expansion, including sustained transmission around the Murray River in Australia in 2021 and 2022, has widened the geography clinicians must keep in mind.
Tick-borne encephalitis is focally endemic in forest and forest-edge habitat from western Europe across to northern and eastern Asia, acquired through the bite of Ixodes ticks or, less often, by drinking unpasteurised dairy. Hikers, campers, foragers and forestry workers in the spring-to-autumn tick season are most exposed. An inactivated whole-virus vaccine given as a three-dose primary course is recommended for those with extensive anticipated tick exposure. It is a distinct product from the Japanese encephalitis vaccine and the two must not be interchanged, a common point of confusion because both are inactivated flavivirus travel vaccines.
Enteric and bloodborne infections with a vaccine
Hepatitis A is the most common vaccine-preventable infection acquired by travellers, spread by the faecal-oral route wherever sanitation is uncertain. The inactivated vaccine, a two-dose course from twelve months of age, is highly effective, and a single dose before departure protects most healthy travellers, since over 90% seroconvert within about a month. A combined hepatitis A and B product offers an accelerated schedule for those leaving at short notice. Older travellers, the immunocompromised and those with chronic liver disease who must leave within two weeks may be given normal human immunoglobulin alongside the first dose.
Hepatitis B is acquired through blood and body fluids, and the travel-specific routes are easy to underestimate: medical or dental care in a setting with imperfect sterilisation, an accident needing transfusion, tattoos and piercings, and sexual contact. The recombinant vaccine can be given on an accelerated schedule and is recommended for longer stays, adventure travel, healthcare or aid work, and any traveller whose plans make exposure plausible.
Poliomyelitis is covered above as a required vaccine; the substance of protection is the inactivated vaccine. An adult who completed a childhood polio series and is travelling to an area with circulating poliovirus should receive a single lifetime booster dose, which both protects them and satisfies the certificate requirement where one applies.
Respiratory and close-contact infections with a vaccine
Measles is the highest-yield item on many pre-travel checklists, because it is intensely transmissible, still circulates widely, and is carried home by the unimmunised. More than 552,000 suspected cases were reported across 179 countries in 2025, a resurgence that has cost several countries their elimination status and is driven largely by travel importation into under-vaccinated communities. Two documented doses of measles-mumps-rubella vaccine, birth before 1957, or laboratory evidence of immunity count as protection; travellers without these should be vaccinated. Infants aged six to eleven months travelling to a risk area should receive an early dose, which does not count toward the routine series and is repeated from twelve months of age.
Influenza is easy to forget as a travel infection, yet it is among the most common. The northern and southern hemispheres have opposite influenza seasons, and in the tropics the virus circulates year-round, so a traveller can meet influenza out of their home season, and enclosed settings such as cruise ships and tour groups concentrate transmission. Annual vaccination is advised, though a traveller vaccinated for their own hemisphere cannot readily obtain the other hemisphere’s formulation. A separate, standing concern is zoonotic avian influenza, notably H5N1, in travellers with close poultry or animal contact, against which the seasonal vaccine gives no protection.
Rabies is almost always fatal once symptomatic and is endemic in dogs across much of Asia, Africa and Latin America, with children at greatest risk. Pre-exposure vaccination is now a simplified two-dose schedule given on days 0 and 7. It does not remove the need for care after a bite, but it transforms it: a previously vaccinated person needs only two further vaccine doses and no rabies immunoglobulin, which is decisive because immunoglobulin is scarce or unavailable across much of the endemic world. Pre-exposure vaccination is therefore recommended for travellers with likely animal contact or poor access to reliable post-exposure care.
COVID-19 circulates worldwide with no settled seasonal pattern, and crowded travel settings favour transmission. Vaccine and booster guidance changes rapidly and should be checked against current national advice at the time of travel; the general principle is that travellers, and especially older or immunocompromised ones, should be up to date before departure.
Travel-associated viral infections without a traveller vaccine
For much of the viral disease travellers actually meet, there is no vaccine for the ordinary traveller, and prevention is behavioural: rigorous avoidance of mosquito bites for the arboviruses, and care with food, water and hygiene for the enteric viruses.
Dengue is the most important arboviral febrile illness of travellers, endemic across more than 100 countries and spread by day-biting Aedes mosquitoes in exactly the urban and residential settings travellers stay in. Most infections are mild or silent, but a second infection with a different serotype carries a higher risk of severe dengue, with plasma leak, bleeding and shock, a phenomenon driven by antibody-dependent enhancement. That same biology makes vaccination hazardous in people who have never been infected. The first vaccine, Dengvaxia, is used only in proven previously-infected residents of endemic areas because it worsens disease in the dengue-naive, and it is being withdrawn. A newer live attenuated tetravalent vaccine, Qdenga (TAK-003), is prequalified by the World Health Organization and recommended for children in high-transmission settings, and is in use across the European Union, the United Kingdom and much of Latin America and Asia with durable multi-year protection; it is not, however, positioned as a routine vaccine for the general traveller and is not available in every market. For most travellers, bite avoidance remains the only measure.
Zika is spread by the same Aedes mosquitoes and is usually mild or asymptomatic, which makes its significance easy to miss: infection in pregnancy is teratogenic, causing congenital Zika syndrome with microcephaly, brain and eye anomalies and fetal loss, and the virus is also linked to Guillain–Barré syndrome. There is no vaccine. Zika is additionally transmissible sexually and persists in semen after the blood has cleared, so the advice is as much reproductive as preventive: pregnant women should avoid travel to areas with active transmission, and after travel couples should prevent conception for a defined interval (about three months for men and two for women) and use strict bite and sexual-transmission precautions.
Chikungunya is an Aedes-borne alphavirus that produces explosive outbreaks with very high attack rates and an acute illness of fever and severe joint pain. The arthralgia is frequently prolonged, persisting for months or years in a substantial minority, and disease is more severe at the extremes of age and in those with comorbidity, with a real risk of transmission to the neonate when a mother is viraemic around delivery. The vaccine picture must be stated carefully. A live attenuated vaccine, IXCHIQ, was licensed in 2023, but its United States licence was suspended in August 2025 after serious adverse events, including deaths, and the manufacturer withdrew it there in January 2026, although it remains authorised in some markets. A virus-like-particle vaccine, VIMKUNYA, was approved in 2025 as a single dose from twelve years of age and is used for travel to areas with active outbreaks. For most travellers, avoiding the day-biting vector remains the mainstay.
Norovirus is the classic enteric outbreak virus of cruise ships, and of any close-quarters setting from camps to conference hotels, spread by the faecal-oral route and by contaminated surfaces and vomit aerosols. The illness is short and self-limiting, dominated by vomiting and watery diarrhoea, with dehydration the main danger at the extremes of age. There is no vaccine, and because the virus is non-enveloped and resistant, handwashing with soap and water is more effective than alcohol hand sanitiser, which is only an adjunct; care with food and water and prompt isolation of the unwell complete the prevention.
Finally, the viral haemorrhagic fevers, though rare in travellers, dominate the early management of the returning febrile traveller out of all proportion to their frequency, because a single missed case is catastrophic. The arenaviruses, filoviruses and the tick-borne Crimean-Congo haemorrhagic fever virus matter to the traveller less for their numbers than for the isolation and infection-control response that a single suspected case triggers.
The returning traveller with fever
Fever after travel is common and usually resolves on its own, but the clinical priority is inverted: the first task is not to name the likely cause but to exclude the few diagnoses that kill quickly or endanger others. The reasoning is built from four questions, asked together: where exactly the traveller went, when the illness began relative to travel, what specific exposures occurred (insect and tick bites, freshwater, food and water, animals, sexual contact, healthcare), and what vaccines or prophylaxis were taken.
Malaria must be actively excluded in every febrile traveller returning from an endemic area, above all sub-Saharan Africa. It is not a virus but a Plasmodium parasite, and it is the single most important differential precisely because falciparum malaria can kill within days and is entirely treatable if caught. A malaria blood film and rapid antigen test are mandatory regardless of whether the traveller took prophylaxis, and a single negative result does not exclude it if suspicion is high. Falciparum malaria takes at least six days to become symptomatic, so a fever in the first days of a trip is not malaria, but the window then extends for weeks to months, so late fever never excludes it.
The incubation period is the most powerful discriminator among the viral causes, and matching the interval since exposure to the illness narrows the field before any test is sent.
| Infection | Typical incubation | Pointer |
|---|---|---|
| Norovirus | 12 to 48 hours | Vomiting, close-quarters outbreak |
| Influenza | 1 to 4 days | Respiratory, cruise or tour group |
| Yellow fever | 3 to 6 days | Jaundice, unvaccinated, endemic area |
| Chikungunya | 2 to 12 days | Severe, often prolonged joint pain |
| Dengue | 4 to 14 days | Myalgia, rash, falling platelets |
| Zika | 3 to 14 days | Mild rash, pregnancy risk |
| Japanese encephalitis | 5 to 15 days | Encephalitis, rural Asia |
| Viral haemorrhagic fevers | Up to 21 days | Bleeding, endemic area, isolate |
| Measles | 7 to 21 days | Rash, coryza, conjunctivitis |
| Falciparum malaria | 6 days or more | Any fever from endemic Africa; exclude first |
| Hepatitis A | 15 to 50 days | Jaundice, faecal-oral exposure |
| Hepatitis E | 15 to 60 days | Jaundice, severe in pregnancy |
| Acute HIV | 2 to 4 weeks | Seroconversion illness after sexual exposure |
| Rabies | Weeks to months | Animal bite; uniformly fatal once symptomatic |
A viral haemorrhagic fever should be suspected in a traveller who develops fever within 21 days of leaving an endemic area, particularly sub-Saharan Africa, with a compatible exposure such as rural residence, healthcare or funeral contact, or contact with rodents, ticks or bushmeat. Suspicion alone changes the setting of care: the patient is isolated with barrier precautions, the case is notified, and the laboratory is warned so that specimens are handled under the right containment. That response runs in parallel with, and never delays, the exclusion of malaria, which remains the more probable and equally urgent diagnosis.
Test selection turns on the timing of the sample relative to symptom onset, the central principle in interpreting travel diagnostics. Early in an acute viral illness the virus itself is detectable and antibody is not, so a nucleic-acid test (reverse-transcription polymerase chain reaction) or an antigen test such as the dengue NS1 assay is the right choice in the first several days. Later, as viraemia falls, serology takes over, but antibody results carry two traps: a single IgG is rarely informative, needing a rising titre in paired samples, and the flaviviruses cross-react extensively, so dengue, yellow fever, Japanese encephalitis and Zika antibodies, and prior yellow fever or Japanese encephalitis vaccination, all confound each other and may require a confirmatory neutralisation test. A test sent at the wrong point in the illness produces a falsely reassuring result.
Special traveller groups
The standard advice bends for travellers whose risk or vaccine eligibility differs, and these groups carry a disproportionate share of serious travel-associated disease.
Pregnant and breastfeeding travellers cannot receive the live vaccines that matter most for travel: yellow fever, measles-mumps-rubella and varicella are all generally contraindicated, and yellow fever is given only when travel to a genuine high-risk area is unavoidable. Pregnancy also raises the stakes of several travel infections, with more severe hepatitis E and malaria and the specific teratogenic threat of Zika, so avoidance often outweighs any vaccine. Inactivated vaccines, including hepatitis A and B and influenza, are safe and frequently indicated.
The immunocompromised, whether from HIV, malignancy, transplantation or immunosuppressive therapy, face the same live-vaccine barrier (yellow fever, measles-mumps-rubella, varicella, oral polio and live oral typhoid are all contraindicated) together with a blunted response to the inactivated vaccines they can receive and a higher risk of severe disease if infected. Their consultation must start earlier and may need post-vaccination serology. A person with well-controlled HIV and a CD4 count of at least 200 may receive yellow fever vaccine, one of the few live vaccines with a defined immunological threshold for safe use.
Older travellers tolerate most vaccines well but warrant particular caution with yellow fever, given the age-related rise in serious vaccine reactions, and benefit from attention to influenza and pneumococcal protection. Infants and children are governed by age thresholds, yellow fever from nine months and an early measles dose from six months, and children carry the highest rabies risk because they approach animals and under-report bites.
The group most often missed is the traveller visiting friends and relatives: people returning to a country of origin to see family, who take fewer precautions, stay longer, live in local rural households rather than hotels, and consequently account for a large share of imported malaria, typhoid and hepatitis A. They benefit most from a deliberate pre-travel consultation and are the least likely to seek one.
Non-viral infections to keep in view
The differential in a returning traveller is not confined to viruses, and a viral reference is incomplete without naming the infections that share the clinical picture. Malaria is the pre-eminent one, addressed above. Enteric fever (typhoid and paratyphoid) is a common cause of undifferentiated fever from South Asia and is vaccine-preventable. Bacterial gastroenteritis, most often from enterotoxigenic Escherichia coli and also Campylobacter, Shigella and Salmonella, is the single most frequent travel illness of all, usually self-limiting and managed by rehydration with selective use of antibiotics. Cholera appears in outbreak and disaster settings, meningococcal disease around the hajj, and rickettsial illness such as African tick-bite fever in safari travellers, often with a tell-tale eschar.
South African context
South Africa sits on both sides of travel medicine. It is not endemic for yellow fever, but it is receptive to it, carrying competent Aedes mosquitoes, and so it enforces the International Health Regulations at its ports of entry: a valid yellow fever certificate is required from travellers arriving from countries with a risk of transmission, which for many regional arrivals is the everyday face of the system. At the same time, South Africans are heavy outbound travellers into yellow fever and malaria-endemic sub-Saharan Africa for business, leisure and to visit family, so pre-travel yellow fever vaccination at a designated centre and malaria chemoprophylaxis for cross-border trips are routine domestic concerns rather than exotic ones. The line between travel and local risk is itself blurred, because malaria transmission continues in the low-lying north-east of the country, in parts of Limpopo, Mpumalanga and northern KwaZulu-Natal.
The returning febrile traveller presenting to a South African facility is worked up malaria-first, reflecting both imported and locally acquired falciparum disease, and then against the viral haemorrhagic fevers, where the local picture has a distinctive feature: Crimean-Congo haemorrhagic fever is endemic within the country through tick and livestock exposure, so a haemorrhagic fever consideration can arise without any international travel at all. Suspected viral haemorrhagic fever, along with measles, rabies and acute flaccid paralysis suggestive of polio, is a notifiable medical condition, and a suspected case triggers immediate notification and the national outbreak response. Current travel-health advice, the list of designated yellow fever vaccination centres and the notifiable-conditions framework are maintained by the National Institute for Communicable Diseases and the National Department of Health.
References and recommended reading
- World Health Organization. International Travel and Health, Chapter 6: Vaccine-preventable diseases and vaccines (2019 update). Geneva: WHO; 2020. The standing international framework for travel vaccination and the vaccine categories used here.
- Centers for Disease Control and Prevention. CDC Yellow Book: Health Information for International Travel, 2026 edition. Oxford University Press; 2025. The current, frequently revised reference for travel-associated infections, vaccines and destination risk.
- World Health Organization. International Health Regulations (2005), third edition, and the 2016 amendment to Annex 7 establishing lifetime validity of a single yellow fever dose. Geneva: WHO. The legal basis for required travel vaccination and the yellow card.
- World Health Organization. Eliminate Yellow Fever Epidemics (EYE) Strategy 2017 to 2026. Geneva: WHO. The global programme underpinning yellow fever prevention in endemic regions.
- Global Polio Eradication Initiative / WHO. Statements of the Polio IHR Emergency Committee (current series). The authority for the temporary polio-vaccination requirements affecting long-stay travellers.
- National Institute for Communicable Diseases (NICD), South Africa. Travel-health guidance, yellow fever vaccination centres and notifiable medical conditions. The South African operational reference.