This large-scale study, the first performed in Spain, offers a first important insight into differences in vaccination between VFR and non-VFR travellers.
It is important to remember that the VFR population differs from travellers other than VFR in sociodemographic characteristics. These travellers, in fact, were younger than non-VFR travellers; were for the most part women; and, as expected, composed mainly of people from non-European countries. The analysis of vaccination rates between the two cohorts indicated some differentials in adherence to immunisation protocols. First of all, it should be noted that the level of completion of those vaccines was not properly related to travel. Indeed, vaccines against influenza, polio, tetanus and both hepatitis A/B and hepatitis B were less likely to be completed by VFR travellers. Regarding hepatitis, noticeable is the scarce level of vaccine completion in the VFR travellers, since their most frequent destinations were in African countries, where hepatitis B is spreading on an endemic level. On this point, previous epidemiological research highlighted that a great percentage of hepatitis B in VFR travellers returning to their residency country are in those coming back from Africa (mainly, from sub-Saharan Africa), where the major epidemiological determinant for hepatitis B infections in VFR travellers is represented by the higher likelihood of sexual encounters with natives during travel . However, a limitation exists because VFR travellers usually do not have a childhood immunisation card, so the prescription is provided during the visit or, if some period of time exists prior to travel, a serology is done to assess the need for immunisation. In Catalonia, travellers born after 1983 have been vaccinated against hepatitis B in adolescence, and all have a childhood immunisation card. Catalan travellers born before 1983 or immigrants without a registry about immunisation are usually prescribed hepatitis B if the endemicity is higher than that in our country.
Migration in Catalonia started at the beginning of the XXI century, so VFRs do not travel much more often than non-VFR travellers. They save money from their arrival to come back home as soon as possible, but it was difficult to travel once during the first decade, because flights were expensive . Therefore, VFR and non-VFR adults, once they are seen at the travel clinic (in a real-life context), probably show that they have not received any vaccine since childhood, and no immunisation history is present, so no difference between them exists .
Low levels of immunisation for the other routine vaccines are likewise a worry; staying too long in rural areas, in close proximity to the local population, in suboptimal hygienic conditions, exposes travellers to diseases from which the population should be protected [2, 3]. In this regard, one of the most relevant challenges in the health care of migrants is represented by the difficulty of obtaining clear information on their immunisation status because of partial or no data regarding previous exposures or vaccinations . This aspect, indeed, forms part of the wider problems of inequalities in access to health services in the countries where migrants live, likely due to sociocultural, economic (costs) and language barriers [16,17,18]. These are the same drivers that—together with others (such as immunisation hesitancy, low risks perception, limited time before the travel, characteristics of the travel and so on)—could probably lead VFR travellers to ignore pre-travel care and advice before they travel. On the other hand, this study can be considered a pragmatic or real-life study, because usually adults in Catalonia do not have an immunisation card, and neither do immigrants.
A constant source of concern about travellers’ health is food and water safety, with special attention to the prevention of traveller’s diarrhoea and other food-related illnesses . VFR travellers are commonly exposed to these risks more than tourists, due to eating contaminated food (crude food, freshwater fish and so on), sharing meals with local hosts and limited access to water. The low level of adherence to hepatitis A, typhoid IM and cholera vaccines among VFR travellers calls attention to the potential implications for their health. One possible explanation for the lower vaccination rate against hepatitis A amongst VFR travellers is that this population might be exposed to the infection in their home-country during childhood, reducing the need for this specific protection. More research should deepen this aspect. However, typhoid fever or cholera should be emphasised in their vaccination regimen because of an increased risk of exposure in rural areas in endemic countries.
Moreover, travelling to remote areas necessarily entails a greater attention to specific risks and demands about immunisation. One of these is represented by the increased exposure to animal bites, even those kept by local families; then protection against rabies becomes important, especially for the high mortality rate of the disease . In this regard, VFR travellers showed significantly less adherence to rabies vaccination than other travellers did.
Interesting, instead, is the finding that the odds of acquiring yellow fever vaccination were twice greater in the VFR population than among non-VFR travellers, partially in accordance with the results reported by Tan et al.  but displaying a lack of concordance if compared to published research conducted to assess travel characteristics about the adherence to yellow fever vaccination . This might be explained by the fact that VFR travellers had planned travels to countries or areas endemic for yellow fever, and they probably are very conscious of the danger of the disease. Another reason that may lead VFR travellers to acquire this vaccine is that travellers are required to present a proof of vaccination to enter certain countries. Indeed, the requirement of a vaccination certificate may explain the higher rate of meningococcal vaccinations among VFR travellers.
Travel destinations and length of stay might influence the level of prescription of antimalarial drugs between the two groups. VFR individuals travelled more to malaria zones than tourists did, so they were prescribed personal protection measures against malaria. However, independent of travel destinations, VFR travellers received more mefloquine than atovaquone-proguanil, probably due to time duration, but we could not confirm this. In South America, neither VFR nor non-VFR travellers usually went to malaria-endemic areas, so we usually did not prescribe antimalarial chemoprophylaxis.
Further studies should highlight the level and drivers of adherence to malaria chemoprophylaxis among VFR travellers, though. For instance, a study by Wieten et al., which only included VFR travellers to West Africa, found that age was positively associated with the probability of receiving pre-travel advice, as well as was a significant factor associated with the behaviours of buying and starting chemoprophylaxis before departure . However, it should be mentioned that the research on the contribution of age on the adherence to malaria prevention measures needs further study .
VFR travellers are recognised as a peculiar traveller population, characterised by special health needs . The presented findings showed a relevant gap in pre-travel care, with alarming differences between non-VFR and VFR travellers, and when rates of vaccination were suboptimal in both groups. Hypothetically, several drivers could be referred to as determinants in those differences. First, VFR travellers could have biased attitudes and perceptions about travel-related health risks, particularly when they are living in a home country with a low gradient of epidemiologic risks that might falsely reassure them, also fostering the belief that they are already immune, thus leading to less use of precautions and fewer personal protection measures than tourists take . On this point, it is also important to highlight that several barriers could affect the pre-travel consultation. Indeed, it constitutes a complex process and its effectiveness strongly depends on relationship between physician and traveller [25, 26]. These are often provided with too much information, which can be misunderstood when communication and language barriers are present, as in the case of VFR travellers.
Finally, it is possible to affirm that specific interventions are needed to promote adherence to pre-travel health advice among VFR travellers, pointing out health education and health promotion for this group population, to achieve an optimal level of protection against travel-related risks [27, 28].
This study may have some methodological limitations that are worthy of emphasis and that should be considered when interpreting the results. First, the cohort nature of the study does not make it possible to establish causal effects. In addition, the database information of the travel clinic attendees did not include data on previous vaccinations (usually not recorded or registered nor provided by travellers), comorbidities (usually travellers say that they do not have any medical condition, and we could not recover data about that) and characteristics other than those mentioned in the Methods section: the possibility that associations found may be explained by other confounders should be taken into account. Second, the study includes only subjects seeking medical advice in our unit and does not include patients seeking it elsewhere or not seeking it at all, so this cohort might be inadequate for determining all the predictors of vaccines and chemoprophylaxis acceptance. Further studies on this issue should be encouraged. However, cohort studies use broader inclusion criteria and fewer exclusion criteria than randomised studies do, making results more generalisable for clinical practice.
Prior to a traveller’s attendance, all travellers are informed about the costs, so when travellers say that they do not want to be vaccinated, they will also pay the medical visit, so it is never an economical reason for why they are not vaccinated. The reasons for not vaccinating are that the inoculations are not mandatory to enter to their destination countries, or they need to receive different or consecutive doses (for example, for rabies). They say that they cannot come again to the travel clinic due to work limitations to obtain a free day for a medical visit.
Despite these limitations, the strengths of this study were that the cohort was properly selected and constituted a large number of participants; the study design was appropriate and the methodology of the study was accurate, reducing problems of bias.