Intradermally administered yellow fever vaccine at reduced dose induces a protective immune response: a randomized controlled non-inferiority trial

BACKGROUND

Implementation of yellow fever vaccination is currently hampered by limited supply of vaccine. An alternative route of administration with reduced amounts of vaccine but without loss of vaccine efficacy would boost vaccination programmes.

METHODS AND FINDINGS

A randomized, controlled, non-inferiority trial was conducted in a Dutch university center between August 2005 and February 2007. A total of 155 primary vaccinated and 20 previously vaccinated volunteers participated. Participants were randomly assigned in a 1ratio1 ratio to receive intradermal (i.d.) vaccination with live attenuated yellow fever 17D vaccine at a reduced dose (1/5(th); 0.1 mL) or the conventional subcutaneous (s.c.) vaccination (0.5 mL). Antibody neutralization titers were determined at 2, 4 and 8 weeks and 1 year after vaccination by counting the reduction in virus-induced plaques in the presence of serial serum dilutions. Adverse events were documented in a 3-week dairy. Viraemia was measured 5 days after vaccination. From 2 weeks up to one year after vaccination, the maximum serum-dilution at which 80% of the virus plaques were neutralized, which indicates protection against yellow fever, did not differ between those given a reduced i.d. dose or standard s.c. dose of vaccine. In all cases the WHO standard of seroprotection (i.e. 80% virus neutralization) was reached (in 77/77 and 78/78, respectively). Similar results were found in the previously vaccinated individuals. Viraemia was detected in half of the primary vaccinated participants, which was not predictive of serological response. In revaccinees no viraemia was detected.

CONCLUSIONS

Intradermal administration of one fifth of the amount of yellow fever vaccine administered subcutaneously results in protective seroimmunity in all volunteers. Albeit this vaccination route should enable vaccination of five-times as many individuals at risk for disease, these results should now be confirmed in field studies in areas with potential yellow fever virus transmission to change vaccination policy.

TRIAL REGISTRATION

Nederlands Trial Register ISRCTN46326316.

Yellow fever vaccine: past, present and future

BACKGROUND

Yellow fever is a re-emerging infectious disease, as vector control and routine immunisation have dwindled in endemic areas in the last few decades. There is a constant threat of outbreaks in the large susceptible non-immune population of the megacities in tropical countries with an ongoing virus life cycle in the rainforests. For this population and for travellers to endemic areas, vaccination is the only effective protective measure against the disease and the spread of the virus.

OBJECTIVE/METHODS

We discuss the history of yellow fever vaccine development, and focus on practical aspects of vaccine safety, contraindications for vaccination, and future vaccine developments.

RESULTS/CONCLUSIONS

Vaccination with the live attenuated yellow fever-17D vaccine (YF-17D) induces low-grade viraemia in half of the vaccinees and elicits protective neutralising antibody levels in 99%. Reports of serious adverse events in the elderly and immunocompromised, and the inability to produce large quantities of yellow fever vaccine at short notice in combination with limited vaccine stockpiles highlight the need for further study of this highly effective and safe vaccine.

Performance of self-diagnosis and standby treatment of malaria in international oilfield service employees in the field

Background

Falciparum malaria remains a major occupational illness that accounts for several deaths per year and numerous lost working days among the expatriate population, working or living in high-risk malarious areas. Compliance to preventive strategies is poor in travellers, especially business travellers, expatriates and long-term travellers.

Methods

In this cross-sectional, web-based study the adherence to and outcome of a preventive malaria programme on knowledge, attitudes and practices, including the practice of self-diagnosis and standby treatment (curative malaria kit, CMK) was evaluated in 2,350 non-immune expatriates, who had been working in highly malaria endemic areas.

Results

One-third (N = 648) of these expatriates visited a doctor for malaria symptoms and almost half (29 of 68) of all hospitalizations were due to malaria. The mandatory malaria training for non-immunes was completed by 92% of those who visited or worked in a high risk malaria country; 70% of the respondents at risk also received the CMK. The malaria awareness training and CMK significantly increased malaria knowledge [relative risk (RR) of 1.5, 95%CI 1.2–2.1], attitudes and practices, including compliance to chemoprophylaxis [RR = 2.2, 95%CI 1.6–3.2]. Hospitalization for malaria tended to be reduced by the programme [RR = 0.4, 95%CI 0.1–1.1], albeit not significantly. Respondents who did not receive instructions on the rapid diagnostic test were two times [RR = 2.3, 95%CI 1.6–3.3] more likely to have difficulties. Those who did receive instructions adhered poorly to the timing of repeating the test. Moreover, 6% (31 of 513) of those with a negative test result were diagnosed with malaria by a local doctor. 77% (N = 393) of the respondents with a negative test result did not take curative medication. 57% (252 of 441) of the respondents who took the curative medication that was included in the kit did not have a positive self-test or clinical malaria diagnosis made by a doctor.

Conclusion

This survey demonstrated that a comprehensive programme targeting malaria prevention in expatriates can be effectively implemented and that it significantly increased malaria awareness.

Reduced intradermal test dose of yellow fever vaccine induces protective immunity in individuals with egg allergy

The neutralising antibody response after the yellow fever vaccine (YF-17D) skin test was measured in 7 egg allergic persons in whom further vaccination was abandoned because of a strong local urticarial reaction to the YF-17D vaccine test dose. We found that this test dose of 0.1mL of YF-17D vaccine was sufficient to induce a protective antibody response in all 7 subjects. Intradermal injection of 1/5th dose of the yellow fever vaccine appears to be sufficient, in non-allergic as well as allergic persons, and non-inferior to the subcutaneous full dose.

Advances and controversies in yellow fever vaccination

Ever since its development in 1937, the live-attenuated 17D yellow fever (YF) vaccine has been one of the most effective vaccines available to man. In this review we highlight the major steps in the development of 17D YF vaccine. We discuss the use of neutralizing antibodies as a surrogate marker for protection, and explore the strengths and weaknesses of the current plaque reduction neutralization test (PRNT), a technique developed in the 1960s that continues to be superior to every modern test in both sensitivity and specificity. The neutralizing antibodies demonstrated by the PRNT can be detected for several decades after vaccination, possibly even for the remainder of the recipient's natural life. We review the available evidence on the duration of protection after primary vaccination, a topic that has been the subject of controversy over the last few months. For persons who are immunocompromised due to disease, medication or advancing age, the duration of protection may be shorter: they should always have their vaccine response checked by PRNT. Due to the higher risk of severe adverse events after vaccination with 17D YF in this group, the development of a new, inactivated vaccine will have substantial benefits in this population.

Knowledge, attitudes, and practices toward malaria risk and prevention among frequent business travelers of a major oil and gas company

BACKGROUND

Despite significant morbidity and mortality among business travelers due to malaria, very little has been published on knowledge, attitudes, and practices (KAP) toward malaria risk. The aim of this study was to assess KAP among frequent international business travelers (FBT) and to identify recommendations for improving malaria prevention that could be applied to the wider FBT community in occupational health.

METHODS

A retrospective web-based survey was conducted in 2005 among self-registered FBT of an oil and gas company based in the Netherlands.

RESULTS

The survey was completed by 328 of the 608 self-registered FBT (54%). Fifty-four percent of respondents had visited a high-risk area for malaria. Most respondents (96%) were experienced travelers; the majority (71%) sought health advice before their trip and made use of a company health resource. Fever was recognized as a malaria symptom by all FBT; travel to high-risk malaria areas was correctly identified by 96%, and 99% of these travelers adhered to use of adequate personal protective measures. The proportion of travelers carrying appropriate anti-malaria drug regimen was positively associated with receiving company advice among FBT traveling to high-risk destinations (RR = 2.10, 95% CI: 1.21-3.67), but not for those traveling to low- or no-risk destinations. Only 8% (14) of those going to a high-risk area were not carrying malaria prophylaxis. One in five of FBT traveling to no-risk areas were unnecessarily carrying malaria prophylaxis.

CONCLUSIONS

The majority of KAP results were excellent. We postulate that a company culture with a strong focus on health, safety, security, and environment can positively contribute to high KAP scores. Notwithstanding the excellent findings, this study also provides a cautionary tale for company health functions against overprescribing of malaria prophylaxis. It demonstrates the need for constant review and audit of adherence to quality criteria.

Intradermal hepatitis B vaccination in non-responders after topical application of imiquimod (Aldara)

BACKGROUND

Five to ten percent of immunocompetent persons fail to develop a protective immune response to hepatitis B vaccination, and are defined non-responders (NR). We investigated the immune response to intradermal hepatitis B vaccination after pre-treatment of the skin with the TLR7 agonist imiquimod.

METHODS

Twenty-one non-responders (anti-HBs <10 IU/l after at least 6 intramuscular hepatitis B vaccinations) were randomly assigned to the control group (N=11) or the experimental group (N=10). Participants in both groups received 3 intradermal (ID) vaccinations with 5 microg HBsAg (0.125 mL) at 0, 1 and 6 months. In the experimental group, the dermal site of injection was pre-treated with 250 mg imiquimod ointment. Anti-HBs antibodies were determined at 0, 1, 2, 6 and 7 months.

RESULTS

In both study groups, 70% of the participants developed a protective immune response (anti-HBs >or=10 IU/l), after the 3rd intradermal vaccination.

CONCLUSION

The application of imiquimod on the skin prior to intradermal vaccination did not enhance the humoral response to hepatitis B vaccine. However, irrespective of imiquimod application, 70% of the NR who had not responded to 6 previous intramuscular vaccinations, developed a protective immune response with high affinity antibodies after 3 ID hepatitis B vaccinations with 5 microg HBsAg.

Symptoms of infectious diseases in travelers with diabetes mellitus: a prospective study with matched controls

BACKGROUND

Travelers with diabetes mellitus to developing countries are thought to have symptomatic infectious diseases more often and longer than travelers without diabetes. Evidence for this is needed. This study evaluates whether travelers with diabetes are at increased risk of symptomatic infectious diseases.

METHODS

A prospective study was performed between October 2003 and February 2008 among adult medication-dependent travelers with diabetes, with their healthy travel companions without diabetes serving as matched controls. Thus, travelers with diabetes and controls were assumed to have comparable exposure to infection. Data on symptoms of infectious diseases were recorded by using a structured diary.

RESULTS

Among 70 travelers with insulin-dependent diabetes, the incidence of travel-related diarrhea was 0.99 per person-month, and the median number of symptomatic days 1.54 per month. For their 70 controls, figures were 0.74 and 1.57, respectively (p > 0.05). Among 82 travelers with non-insulin-dependent diabetes, incidence was 0.75, and the median number of symptomatic days was 1.68. For their 82 controls, figures were 0.70 and 1.68, respectively (p > 0.05). As for other symptoms, no significant travel-related differences were found. Only 17% of travelers with diabetes suffering from diarrhea used their stand-by antibiotics.

CONCLUSIONS

Medication-dependent travelers with diabetes traveling to developing countries do not have symptomatic infectious diseases more often or longer than travelers without diabetes. Routine prescription of stand-by antibiotics for travelers with diabetes to areas with good health facilities is probably not more useful than for healthy travelers.

Hepatitis B vaccination strategy in vaccine low and non-responders: a matter of quantity of quality?

Hepatitis B virus infection can lead to chronic infection and liver failure. Transmission of the virus is preventable though vaccination. Unfortunately, 5-10% of healthy individuals and 40-50% of haemodialysis patients do not develop an adequate immune response against the vaccine. In this commentary we focus on the possible biological mechanisms of hepatitis B vaccine unresponsiveness, and give practical advice to overcome this unresponsiveness.