The immunogenicity of a modified intradermal pre-exposure rabies vaccination schedule--a case series of 420 travelers

Immunogenicity and one-year boostability of a 3-dose intramuscular rabies pre-exposure prophylaxis schedule in adults receiving immunosuppressive monotherapy: a prospective single-Centre clinical trial

BACKGROUND

For immunocompromised patients (ICPs), administration of rabies immunoglobulins (RIG) after exposure is still recommended regardless of prior vaccination, due to a lack of data. We aimed to assess the one-year boostability of a 3-dose rabies pre-exposure prophylaxis (PrEP) schedule in individuals using immunosuppressive monotherapy.

METHODS

In this prospective study, individuals on immunosuppressive monotherapy with a conventional immunomodulator (cIM) or a TNF-alpha inhibitor (TNFi) for a chronic inflammatory disease received a 3-dose intramuscular PrEP schedule (days 0,7,21-28) with 1 mL Rabipur®, followed by a 2-dose simulated post-exposure prophylaxis (PEP) schedule (days 0,3) after 12 months. Rabies neutralizing antibodies were assessed at baseline, on Day 21-28 (before 3rd PrEP dose), Day 60, Month 12 and Month 12 + 7 days. The primary outcome was one-year boostability, defined as the proportion of patients with a neutralizing antibody titre of ≥ 0.5 IU/mL at Month 12 + 7 days. Secondary outcomes were geometric mean titres and factors associated with the primary endpoint.

RESULTS

We included 56 individuals, of whom 52 completed the study. The one-year boostability was 90% (47/52) with a GMT of 6.16 (95% CI 3.83-9.91). All participants seroconverted at some point in the study. Early response to PrEP (at day 21-28) was significantly associated with 100% boostability (Odds ratio 51; 95% confidence interval [5.0-6956], p < 0.01). The vaccination schedule was safe and well tolerated. No vaccine-related serious adverse events occurred.

CONCLUSION

In patients using immunosuppressive monotherapy, a 3-dose rabies PrEP schedule followed by a 2-dose PEP schedule is immunogenic, with all patients seroconverting at some point in the study. Although boostability 7 days after PEP was not 100%, nobody would wrongly be denied RIG when only administered to those who responded early to PrEP, while reducing administration of RIG by 73%.

Immunogenicity of a single fractional intradermal dose of Japanese encephalitis live attenuated chimeric vaccine

BACKGROUND

Japanese encephalitis (JE) is endemic in Asia and the western Pacific. Vaccination is recommended for travellers to endemic regions, but the high cost of the vaccine is a major barrier to uptake.

METHODS

A quasi-experimental, pre-post intervention clinical trial without a control group was conducted to assess the immunogenicity and safety of intradermal (ID) JE vaccine. Healthy adults (18-45 years) received one dose of 0.1 mL (20% of standard dose) ID Imojev® (JE live attenuated chimeric vaccine, Sanofi-Aventis). Adverse events following immunisation (AEFIs) were recorded 10 days post-vaccination. Blood samples were collected at baseline, 4, and 8 weeks post-vaccination. Neutralising antibodies were measured using 50% plaque reduction neutralisation test (PRNT50). Seroconversion was defined as PRNT50 titre ≥10. An in vitro study was also conducted to quantify the rate of decay of vaccine potency after reconstitution.

RESULTS

51 participants (72.6% females, median age 31 years), all non-reactive to JE virus at baseline were enrolled. Mild and moderate AEFIs were reported by 19.6% of participants; none required medical attention or interfered with normal daily activities. All participants seroconverted at 4 weeks (GMT 249.3; 95%CI:192.8-322.5) and remained seropositive at 8-weeks (GMT 135.5; 95%CI:104.5-175.6). Vaccine potency declined at a rate of 0.14 log plaque-forming units/0.5 mL per hour.

CONCLUSIONS

In healthy adults, a single 0.1 mL ID dose of Imojev was safe and immunogenic, at least in the short-term. Reconstituted vials of Imojev vaccine may not retain their potency after 6 hours. Fractional JE ID vaccination could be a cheaper yet effective alternative for short-term travellers. Further studies need to investigate the immune response in a wider age range of individuals and the long-term immunogenicity of fractional JE ID vaccines.

CLINICAL TRIALS REGISTRATION

ACTRN12621000024842.

One-week intramuscular or intradermal pre-exposure prophylaxis with human diploid cell vaccine or Vero cell rabies vaccine, followed by simulated post-exposure prophylaxis at one year: A phase III, open-label, randomized, controlled trial to assess immunogenicity and safety

Shorter rabies pre-exposure prophylaxis (PrEP) regimens may offer improved convenience and feasibility over classic 3-week regimens, for example in regions with poor access to vaccines or for travelers to rabies-endemic regions. In this multicenter, open-label, controlled trial, 570 healthy participants aged 2-64 years were randomized to receive: 1-week PrEP (vaccination days [D]0 and 7; Group 1) or classic 3-week PrEP regimen (D0, D7, and D21; Group 2) with one 1.0 mL intramuscular [IM] dose of human diploid cell culture rabies vaccine (HDCV) at each visit; 1-week PrEP with two 0.1 mL intradermal (ID) HDCV doses at each visit (Group 3); or 1-week PrEP with one 0.5 mL IM dose (Group 4) or two 0.1 mL ID doses (Group 5) of Vero cell rabies vaccine (PVRV) at each visit. Participants received simulated post-exposure prophylactic (PEP) vaccination (two IM or ID doses of HDCV or PVRV three days apart) one year later. Rabies virus neutralizing antibody titers and seroconversion (titers ≥ 0.5 IU/mL) rates were assessed 14 days and up to 1 year post-PrEP, and pre- and post-PEP. Safety was assessed throughout the study. Seroconversion rates were high 14 days post-last PrEP injection (ranging from 96.7 % to 97.2 % across groups 1, 3-5; 1-week PrEP) and reached 100 % in Group 2 (3-week PrEP). Non-inferiority of Group 1 versus Group 2 in terms of seroconversion rates 14 days post-last PrEP injection (primary objective) was not demonstrated. After simulated PEP, all groups showed rapid and robust immune responses, with all but one participant achieving seroconversion (titers ≥ 0.5 IU/mL). There were no safety concerns, and the tolerability profiles of the vaccines were similar across the groups. A 1-week, IM or ID PrEP regimen with HDCV or PVRV provided efficacious priming, enabling rapid robust anamnestic responses to simulated PEP 1 year later across age groups. ClinicalTrials.gov number: NCT03700242. WHO Universal Trial Number (UTN): U1111-1183-5743.

Long-term persistence of antibodies and boostability after rabies intradermal pre-exposure prophylaxis

BACKGROUND

Currently, there is limited data on long-term persistence of antibodies and boostability of intradermal (ID) rabies pre-exposure prophylaxis (PrEP) schedules. This study investigated travellers who received a primary ID PrEP schedule at least 5 years previously to determine the persistence of antibodies and subsequent antibody response after one 0.1-ml ID booster dose.

METHODS

Adults (age ≥ 18 years) who had previously received ID PrEP at a specialist travel medicine clinic in Brisbane, Australia were included. At Day 0, blood was collected for serology and one dose of 0.1-ml ID rabies vaccine (Verorab®) was administered. At Day 7, serology was repeated. At Day 14, participants were given results and enquired if they experienced adverse events following immunization (AEFIs). Antibodies were measured using Platelia Rabies II ELISA; levels ≥0.5 EU/mL were considered antibody-positive.

RESULTS

158 participants were included [64.6% female, median age at enrolment 56.4 years, interquartile range (IQR) 42.4-65.2 years], and median time since the primary ID PrEP was 8.5 years (IQR 6.9-11.7 years). The majority of participants (82.3%) were antibody-positive at Day 0. The proportion of participants who were antibody-positive at Day 0 was higher among those who were younger at primary vaccination (87.0% if aged<50 years, 75.8% of aged ≥50 years). The proportion of participants who were antibody-positive declined as median time since primary vaccination increased, though the trend was not statistically significant (p-trend = 0.187). All except one participant (99.4%) were antibody-positive after one ID booster dose. AEFIs were reported by 42.4% of participants and were mainly mild.

CONCLUSIONS

Rabies antibodies persist for many years after ID PrEP and can be rapidly boosted with a single ID dose. Future studies are needed to confirm that ID PrEP primes the immune system sufficiently so that boosters are not routinely needed, and only given in the event of a rabies-prone exposure.

Antibody response to rabies pre-exposure vaccination among village health volunteers in a northern region of Thailand

BACKGROUND

Rabies is a lethal, however the disease is preventable through vaccination either before or immediately after an exposure. This study aimed to provide a pre-exposure prophylaxis rabies immunization to village health volunteers (VHV) who provide rabies vaccination for pets and free-roaming dogs in their villages and evaluate the antibody level and adverse effects after vaccination. We also assessed the knowledge related to rabies of these VHVs before field trip for pet vaccination.

METHODS

This study was conducted at Mae Kha sub district, San Pa Tong district, Chiangmai, Thailand between January and March 2020. Consenting participants were interviewed using a questionnaire, received an intradermal two-dose, seven-day pre-exposure rabies vaccination, and sera were tested for anti-rabies antibody levels with the cost effective easy competitive enzyme-linked immunosorbent assay (CEE-cELISA) before and after vaccination.

RESULTS

A total of 27 VHVs were recruited from 14 villages in Mae Kha sub district. All of them were male and had a median age of 61.5 years (interquartile range: 55-64). After vaccination, seroconversion rate was 92 % (23/25) with a median of 12.4 EU/mL (interquartile range: 8.9-20.1). Two participants who had rabies vaccination one year previously still had adequate levels before receiving a booster dose. All participants did not show any serious adverse reactions after vaccination.

CONCLUSION

A regimen of two-dose, seven-day vaccination series in high-risk health volunteers using an intradermal administration provides a high seroconversion rate, efficacy and safe for pre-exposure vaccination schedule. In addition, rabies-related knowledge should be provided to village health volunteers before their fieldwork.

Efficacy of one-dose intramuscular rabies vaccine as pre-exposure prophylaxis in travellers

BACKGROUND

Current guidelines for rabies pre-exposure prophylaxis (PrEP) recommend multiple vaccine doses. Travellers sometimes present for pre-travel consultation with insufficient time to complete standard PrEP schedules. We investigated the efficacy of one-dose intramuscular (IM) vaccine in priming the immune system (as PrEP) by measuring antibody response to simulated post-exposure prophylaxis (PEP).

METHODS

A quasi-experimental pre-post intervention clinical trial was conducted at a specialist travel clinic in Australia. Adults (≥18 years) without a history of rabies vaccination were included. At Visit 1, seronegative status was confirmed and one dose of 0.5 ml IM rabies vaccine (Verorab®) administered. At Visit 2 (≥60 days after Visit 1), serology was repeated and a simulated PEP dose (0.5 ml IM) given on this day and again 3 days later (Visit 3). Serology was repeated at Visit 4 (7 days after Visit 2).

RESULTS

A total of 94 antibody-negative participants were included (<50 years [n = 50]; ≥50 years [n = 44]). At Visit 2, 38.0 and 31.8% of participants aged <50 and ≥50 years were antibody-positive (≥0.5 EU/ml). At Visit 4, all participants were antibody-positive; 82.0 and 47.7% of participants aged <50 and ≥50 years had antibody levels >4 EU/ml, respectively.

CONCLUSIONS

One-dose IM vaccine was effective as PrEP for priming the immune system in both age groups, resulting in rapid development of antibodies 7 days after commencing simulated PEP. If there is insufficient time to complete a standard PrEP schedule, one-dose IM could be considered as an alternative schedule for short trips, rather than not offering travellers any doses at all.Clinical trials registration: ACTRN12619000946112.

Systematic Booster after Rabies Pre-Exposure Prophylaxis to Alleviate Rabies Antibody Monitoring in Individuals at Risk of Occupational Exposure

Pre-exposure rabies prophylaxis (PrEP) is recommended for people at frequent or increased risk of professional exposure to lyssavirus (including rabies virus). PrEP provides protection against unrecognized exposure. After the primary vaccination, one's immune response against rabies may decline over time. We aimed to evaluate the immune response to rabies in individuals immunized for occupational reasons before and after a booster dose of the rabies vaccine. With this aim, we retrospectively documented factors associated with an inadequate response in individuals vaccinated for occupational purposes. Our findings analyzed data from 498 vaccinated individuals and found that 17.2% of participants had an inadequate antibody titration documented after their primary vaccination without the booster, while inadequate response after an additional booster of the vaccine was evidenced in 0.5% of tested participants. This study showed that a single booster dose of vaccine after PrEP conferred a high and long-term immune response in nearly all individuals except for rare, low responders. A systematic rabies booster after primary vaccination may result in alleviating the monitoring strategy of post-PrEP antibody titers among exposed professionals.

Immunogenicity after pre- and post-exposure rabies vaccination: A systematic review and dose-response meta-analysis

BACKGROUND

There are a myriad of vaccine schedules for rabies pre- (PrEP) and post-exposure prophylaxis (PEP) that differ in the number and timedoses, number of visits, length of schedule, and route of administration. The objective of this study was to systematically review the evidence and investigate how thedifferences in schedules influence titres over time.

METHODS

Four databaseswere searched from inception to January 2020 for rabies PrEP and PEP studies. Adose-response meta-analysis was utilised to pool geometric mean titres (GMT) over time. Subgroup analyses by route of administration, age group, and schedule were conducted.

RESULTS

80 studies met the inclusion criteria and contributed with 191 datasets and 12,413 participants. Both intradermal (ID) and intramuscular (IM) PrEP/PEP produce adequate GMTs. Significantly lower GMT levels were achieved in older (>50yrs) compared to younger (<50yrs) participants. Short 1-week schedules were as effective as longer schedules that can take between 3 and 12 weeks to complete.

CONCLUSIONS

Several effective ID and IM schedules were identified, the selection of a schedule should take into account the patient's needs, costs, availability to return for subsequent doses, and the time required to complete the schedule. Older individuals warrant special attention as they develop lower antibody response.

Intradermal rabies pre-exposure vaccination schedules in older travellers: comparison of immunogenicity post-primary course and post-booster

BACKGROUND

Intradermal (ID) rabies vaccination for pre-exposure prophylaxis (PrEP) has become increasingly popular; however, there is limited evidence about the effectiveness of different ID PrEP schedules in travellers aged > 50 years or their response to ID boosters. This study aimed to compare across different ID vaccine schedules and age groups the proportion of travellers who were seropositive after (i) primary course of ID PrEP and (ii) a booster.

METHODS

Travellers who received ID PrEP at a travel medicine clinic in South Australia from 2000 to 2016 were included. Three schedules were examined: 1IDx3 (1 × 0.1 ml on days 0, 7, 21-28), 2IDx2 (2 × 0.1 ml on days 0, 7) and 4IDx1 (4x0.1 ml on day 0). The 4IDx1 is a non-standard schedule that has been previously explored in research settings, but not endorsed by WHO for PrEP. Antibody titres of ≥0.5 IU/ml were considered seropositive. The proportion seropositive after a primary course or post-booster was estimated for each schedule and age category. Predictors of seronegative status after a primary course were examined using multivariable logistic regression models.

RESULTS

Overall, 835 travellers (median age 37.5 years; 37.1% > 50 years) were included in the analyses of seropositivity after a primary course. Another group of 771 travellers (median age 45.9 years; 43.5% > 50 years) was included in the analyses of seropositivity post-booster. The proportion seropositive after primary course was 92.5% (95%CI: 90.5-94.1%) and highest with the 1IDx3 schedule (93.4%; 95%CI: 91.4-95.0%). After adjusting for age and timing of the serology, the odds of seronegative status were four times higher (OR 4.17; 95%CI: 1.43-12.18) with the 4IDx1 schedule compared to 1IDx3. Overall, 98.7% (95%CI: 97.6-99.3%) were seropositive post-booster. Of 46 travellers who received a booster ≥3 years after PrEP, all were seropositive post-booster.

CONCLUSIONS

In older travellers, the 1IDx3 schedule was the most effective, and a high proportion were seropositive post-booster even many years after a primary course.

Comparative Immunogenicity and Safety Trial of 2 Different Schedules of Single-visit Intradermal Rabies Postexposure Vaccination

BACKGROUND

Effective and safe single-visit rabies vaccination for pre- and postexposure prophylaxis (PrEP and PEP) could substantially simplify rabies prevention and therefore increase compliance.

METHODS

In a comparative trial, 303 healthy adults received a primary vaccination that consisted of 2 intradermal (ID) doses of 0.1 mL of the purified chicken embryo cell vaccine (PCEV) during a single visit. One year later, participants were randomly assigned to receive either 4 or 2 ID PEP booster doses of 0.1 mL PCEV during a single visit. The primary endpoint for immunogenicity was the percentage of participants with an adequate antibody level (>0.5 IU/mL) 7 days after the booster doses. The safety endpoint was the proportion of participants who developed adverse events (AEs) following primary and/or booster vaccination.

RESULTS

All participants, except 1 (99.3%) in each study group, had a rabies antibody titer >0.5 IU/mL on day 7 following the booster schedules. Participants exposed to the 4-dose PEP schedule had a geometric mean titer of 20 IU/mL vs 14 IU/mL for the 2-dose PEP schedule (P = .0228). Local reactions at the injection site following PrEP and PEP were mild and transient and only seen in 14.9% and 49.6%-53% of the participants, respectively. No serious AEs were reported.

CONCLUSIONS

In healthy adults, a 2-dose (2 × 0.1 mL) single-visit ID PEP schedule was as immunologically adequate and safe as a 4-dose (4 × 0.1 mL) single-visit PEP schedule 7 to 28 months following a 2-dose (2 × 0.1 mL) single-visit ID PREP.

CLINICAL TRIALS REGISTRATION

EudraCT 2014-00183612.

Factors influencing the immune response after a single-dose 3-visit pre-exposure rabies intradermal vaccination schedule: A retrospective multivariate analysis

BACKGROUND

The World Health Organization (WHO) recommends intradermal (ID) rabies vaccination as a safe and immunogenic alternative to intramuscular administration. The aim of this study is to determine which factors influence the levels of rabies virus neutralizing antibodies (RVNA) after a 3-visit ID rabies vaccination.

METHODS

This is a retrospective secondary data analysis study based on electronic health record vaccination data of Belgian military subjects who received ID rabies Pre-exposure prophylaxis (PrEP) with a single-dose 3-visit regimen during the period 2014-2017. Logistic regression was performed to identify predictive factors of RVNA level ≥3.0 IU/mL and >10 IU/mL.

RESULTS

The second analysis performed on the 2025 subjects (100% seroconverted with a RVNA ≥ 0.5 IU/mL) shows a significantly better immune response in subjects younger than 30 years compared to all other age-groups, a gender-difference to predict RVNA ≥ 3.0 IU/mL (OR 2.30 [1.26-4.22] comparing "female" to "male") and the influence of the vaccination schedule (OR 2.28 [1.15-4.53] comparing "late - very variable" to "correct" schedule) to predict > 10 IU/ml. Multivariate analysis also demonstrates that a postponed serology control significantly influences the Rapid Fluorescent Focus Inhibition Test (RFFIT).

CONCLUSION

Gender and age significantly influence the response to ID rabies vaccine. Timing of RVNA determination is important to correctly assess the response to vaccination. A single-dose 3-visit ID rabies PrEP schedule is a dose-sparing effective alternative to the double-dose 2-visit ID schedule. When the minimum time interval between doses is respected, RVNA determination is not necessary.

Timing of Intradermal Rabies Pre-exposure Prophylaxis Injections: Immunological Effect on Vaccination Response

INTRODUCTION

Rabies remains a global threat, with annually over 59,000 deaths. Intradermal (ID) pre-exposure prophylaxis (PrEP) is very efficient and reduces the need for rabies immunoglobulins. Not much is known about factors that influence the immune response to ID administered rabies vaccine. The aim of this study is to determine if variations in timing of vaccine administration and serology determination, age and gender have an influence on the levels of rabies virus neutralizing antibody (RVNA) after ID rabies vaccination.

MATERIALS AND METHODS

This is a retrospective study based on electronic health record vaccination data of Belgian military personnel who received ID rabies PrEP with a three injections regimen during the period 2014-2017. Serology was determined by using the RFFIT method. Fischer's exacts tests were used to evaluate the effect of each independent variable on RVNA levels.

RESULTS

In this study, 2,112 subjects were included. All but one seroconverted with a RVNA level ≥0.5 IU/mL. About 48% of subjects developed an antibody titer of >10 IU/mL, 36% had antibody levels 3-10 IU/mL and 16% had an antibody level 0.5-2.99 IU/mL. Statistically significant (p = 0.0018) higher RVNA levels are observed in the groups that received vaccination doses later as planned. Timing of serology determination also influenced RVNA levels significantly (p = 0.000). Antibody levels were significantly higher in females than in males (p = 0.000). Age did influence RVNA levels significantly (p = 0.022).

CONCLUSIONS

Timing of vaccine dose administration, timing of serology testing, sex and age do significantly influence the humoral B-cell response to ID administered rabies vaccine.

Immune response to rabies post-exposure prophylaxis in patients with non-HIV secondary immunodeficiencies

BACKGROUND

This study sought to determine the proportion of individuals with non-HIV secondary immunodeficiencies presenting inadequate antibody titers after rabies post-exposure prophylaxis (PEP) and to identify variables associated with inadequate response.

METHODS

A retrospective review of the records of immunocompromised patients having received a full course of PEP after a rabies exposure and having been tested for post-PPE antibody titers in two French Antirabies Clinics, between 2013 and 2018, was conducted. Antibody titers < 0.5 EU/ml (ELISA) were classified as inadequate.

RESULTS

A total of 28 individuals were included, 6 had inadequate post-PPE titers. None of the tested variable was independently associated with inadequate titers.

CONCLUSIONS

Inadequate response was unpredictable and not explained either by the characteristics of patients or by the PEP regimen they received. These findings support the WHO recommendation to systematically assess post-PEP response in immunocompromised patients to detect non-responders, who might require an additional dose.

Single-visit, 4-site intradermal (ID) rabies vaccination induces robust immune responses 5 years after 1-week, 4-site ID primary post-exposure prophylaxis in the Philippines

BACKGROUND

In a randomized controlled study (NCT01622062) a 1-week, 4-site intradermal (ID, 4-4-4-0-0) post-exposure prophylaxis (PEP) rabies vaccination regimen with purified Vero cell rabies vaccine (PVRV, Verorab®, Sanofi Pasteur), either without (Group 1) or with (Group 2) purified equine rabies immunoglobulin (ERIG), patients in the Philippines achieved seroconversion rates at Day 14 that were non-inferior to that of the updated Thai Red Cross (TRC) 28-day, 2-site (2-2-2-0-2) ID regimen with ERIG (Group 3). Presented here are the annual immunogenicity data up to five years after the last primary dose, and the immunogenicity and safety data following simulated PEP with single-visit, 4-site ID regimen.

METHODS

Rabies virus neutralizing antibodies (RVNA) were determined by rapid fluorescent focus inhibition test (RFFIT). Participants (n = 397) received simulated PEP vaccination ID at Year 5 and RVNAs were assessed at Day 11 post-vaccination.

RESULTS

Seroconversion rates (RVNA titres ≥ 0.5 IU/mL) during annual follow-up remained >95% in Group 1 and were relatively stable at 80-90% in Group 2, but decreased from 80% to 64% in Group 3. RVNA geometric mean titres (GMTs) in Group 1 were consistently higher than in the other two groups, and those in Group 3 were generally lower than in the other two groups. There was a clear anamnestic response to vaccination in all groups, with all participants achieving RVNA titres ≥ 0.5 IU/mL at Day 11 post-simulated PEP booster vaccination. There were no safety concerns raised during annual follow-up and with simulated post-exposure vaccination with PVRV.

CONCLUSION

The shortened, 1-week, 4-site ID regimen with PVRV achieved persistently higher RVNA titres than the updated 2-site TRC regimen, and more participants remained seroprotected up to five years after the last dose of primary immunization. Simulated post-exposure with 4-site ID rapidly induced an anamnestic response indicative of robust protection.

Preexposure Intradermal Rabies Vaccination: A Noninferiority Trial in Healthy Adults on Shortening the Vaccination Schedule From 28 to 7 Days

Background

The existing 4-week preexposure rabies vaccination schedule is costly and often not practicable. Shorter effective schedules would result in wider acceptance.

Methods

We conducted a noninferiority trial in 500 healthy adults comparing the safety and immunogenicity of a 2-visit (days 0 and 7) intradermal (ID) primary vaccination (2 doses of 0.1 mL ID of the human diploid cell culture rabies vaccine [HDCV] at days 0 and 7) vs a standard 3-visit schedule (single dose of 0.1 mL ID at days 0, 7, and 28). One year to 3 years after primary vaccination, a single booster dose of 0.1 mL ID of HDCV was given to evaluate the anamnestic rabies antibody response. The primary endpoint for immunogenicity was the percentage of subjects with an adequate antibody level >0.5 IU/mL 7 days after the booster injection. The safety endpoint was the proportion of participants developing adverse reactions following the primary vaccination and/or booster dose.

Results

All subjects in both study groups possessed a rabies antibody titer >0.5 IU/mL on day 7 following the booster dose. Following the booster dose, subjects exposed to the double-dose 2-visit ID schedule had a geometric mean titer of 37 IU/mL, compared with 25 IU/mL for the single-dose 3-visit schedule (P < .001). Local reactions at the injection site following primary vaccination were mild and transient.

Conclusions

In healthy adults, ID administration of a double dose of 0.1 mL of HDCV over 2 visits (days 0 and 7) was safe and not inferior to the single-dose 3-visit schedule.

Clinical Trials Registration

NCT01388985, EudraCT 2011-001612-62.

Factors influencing the immune response after a double-dose 2-visit pre-exposure rabies intradermal vaccination schedule: A retrospective study

BACKGROUND

Double-dose 2-visit intradermal rabies schedules (2²ID) have recently been accepted by the World Health Organization (WHO) as Pre-Exposure Prophylaxis (PrEP). The aim of this study is to determine which factors influence the levels of rabies virus neutralizing antibodies (RVNA) after a 2²ID rabies vaccination schedule.

METHODS

This is a retrospective study based on electronic health record vaccination data of subjects from the Belgian Armed Forces who received the 2²ID rabies PrEP. An antibody titer ≥0.5 IU/mL, measured by rapid fluorescent focus inhibition test, is defined by the WHO as an adequate immune response after PrEP. Logistic regression was performed in order to identify predictive factors of RVNA level ≥3.0 IU/ml and >10 IU/ml.

RESULTS

301 subjects were included. 297 (98,6%) seroconverted with a RVNA ≥ 0.5 IU/ml. Multivariate analysis shows a significant better immune response in the subjects where the second dose was administered later on than on day 7 (RVNA >10 IU/ml (OR: 3.01 [1.36-6.67])). Postponing the timing of the serology control also influenced significantly the rapid fluorescent focus inhibition test (RVNA ≥ 3.0 IU/ml (OR: 0.12 [0.06-0.24]) and RVNA > 10 IU/ml (OR: 0.14 [0.06-0.29])).

CONCLUSION

A 2²ID rabies PrEP vaccination schedule is highly effective and provides an adequate immune response in most subjects in a real live setting. Timing of the second vaccine dose significantly influences the response to ID rabies vaccine. Timing of RVNA determination is important in order to correctly assess the response to vaccination.

A randomized open-label trial of 2-dose or 3-dose pre-exposure rabies prophylaxis among Thai children

BACKGROUND

World Health Organization changed the recommendation for pre-exposure rabies prophylaxis from 3-dose to 2-dose regimen in 2018. Given limited data of 2-dose regimens in pediatric population, this study aimed to compare the immunogenicity between 2-dose and 3-dose pre-exposure rabies immunization.

METHODS

This study was conducted among healthy children aged 2-12 years. They were randomized to 2-dose vaccination (2D) on days 0 and 28 or 3-dose vaccination (3D) on days 0, 7, and 28. Purified Vero cell rabies vaccine (PVRV-Verorab™) was administered intramuscularly. Rabies virus neutralizing antibody (RVNA) titers were measured at 3 time points: 14-day after complete vaccination, 1-year pre-booster vaccination, and 7-day post-booster dose to mimic scenario of rabies exposure. RVNA titers ≥0.5 IU/ml were considered adequate antibody. T cell specific response to rabies vaccine antigen was measured using the interferon-gamma enzyme linked immunospot assay.

RESULTS

From September to October 2017, 107 participants (51% males), 78 in 2D group and 29 in 3D group were enrolled. Median age was 5.8 years (IQR 4.4-7.3). All participants had RVNA titers ≥0.5 IU/ml after primary vaccination [GMT 2D: 18.6 (95%CI 15.9-21.8) and 3D: 16.3 (95%CI 13.2-20.1 IU/ml), p = 0.35]. At 1-year prior to receiving the booster, only 80% of the children in 2D group maintained RVNA titers ≥0.5 IU/ml compared to 100% of the children in 3D group (p = 0.01). However, all participants in both groups had RVNA ≥0.5 IU/ml at 7-day post booster vaccination [GMT 2D: 20.9 (95%CI 17.4-25.3) and 3D: 22.2 (95%CI 15.8-31.4) IU/ml (P = 0.75)]. The median number of IFN-γ secreting cells at 7-day post-booster dose was 98 and 128 SFCs per 10⁶ PBMCs in the 2D and 3D groups, respectively (P = 0.30).

CONCLUSIONS

Two-dose primary rabies immunization provided adequate antibody at post primary vaccination and post booster. The results support 2-dose regimen of pre-exposure rabies immunization in the pediatric population.

Intradermal post-exposure rabies vaccination with purified Vero cell rabies vaccine: Comparison of a one-week, 4-site regimen versus updated Thai Red Cross regimen in a randomized non-inferiority trial in the Philippines

BACKGROUND

Rabies post-exposure prophylaxis (PEP) via intradermal (ID) administration is standard practice in Asia. Accumulating evidence suggests that PEP shortened to 3 visits in one week does not adversely affect seroconversion rates or immune memory.

OBJECTIVE

To determine whether the seroconversion rate at Day14 with a 1-week, 4-site (4-4-4-0-0) ID vaccination regimen with or without rabies immunoglobulin (RIG) was non-inferior to the updated Thai Red Cross (TRC) 28-day, 2-site (2-2-2-0-2) ID regimen with RIG during rabies PEP. We also assessed one-year antibody persistence.

METHODS

This phase III, mono-center, open-label, randomized-controlled trial assigned participants aged ≤50 years (n = 600) exposed to suspected rabid animals and sustaining WHO Category II injuries (automatic allocation to G1) or Category III injuries (randomized to G2 or G3) to the following groups (1:1:1 ratio): G1 (n = 200), 1-week 4-site ID regimen with the purified Vero cell rabies vaccine (PVRV; Verorab®) without RIG; G2 (n = 201), 1-week 4-site ID regimen with PVRV, and purified equine rabies immunoglobulin (pERIG); G3 (n = 199), TRC 28-day, 2-site ID regimen with PVRV, and pERIG. Non-inferiority tests compared G1 vs. G3 and G2 vs. G3. Seroconversion rate was the proportion (%) of vaccinees with rabies virus neutralizing antibodies (RVNA) titers ≥0.5 IU/mL measured by rapid fluorescent focus inhibition test.

RESULTS

On Day14, after the third vaccine administration, seroconversion rates were non-inferior in both comparisons and were, respectively, 100%, 99.4%, 98.8% in G1, G2, G3 with a decrease to 97.6%, 89%, 79.8% at Year 1. At Day14, RVNA geometric mean titers were 11.3 IU/mL; 9.89 IU/mL; 6.15 IU/mL, respectively, decreasing to 2.96 IU/mL, 1.37 IU/mL, 0.97 IU/mL at Year1. Safety and tolerability were similar between the three groups.

CONCLUSION

The seroconversion rate at Day 14 with the 1-week 4-site ID regimen, both with and without pERIG, was non-inferior to the reference TRC 28-day 2-site ID regimen with pERIG during rabies PEP with PVRV. ClinicalTrials.gov ID: NCT01622062.

Factors That Influence the Immune Response to Vaccination. Clin Microbiol Rev. 2019;32. [PMID: 30867162 DOI: 10.1128/cmr.00084-18]

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

Survey of rabies vaccination status of Queensland veterinarians and veterinary students

BACKGROUND

To determine the rabies vaccination status of Queensland veterinarians and veterinary students and their perception of zoonotic risk from Australian bat lyssavirus (ABLV).

DESIGN

Cross-sectional questionnaire surveys.

METHODS

Questionnaires were sent by post in 2011 to veterinary surgeons registered in Queensland, to final-year veterinary students at James Cook University via SurveyMonkey® in 2013 and to final-year veterinary students at James Cook University and University of Queensland via SurveyMonkey® in 2014.

RESULTS

The response rate for registered veterinarians was 33.5% and for veterinary students 33.3% and 30% in 2013 and 2014, respectively. Of the 466 registered veterinary surgeons, 147 (31.5%) had been vaccinated, with 72 (15.5%) currently vaccinated. For veterinary students the rabies vaccination rate was 20.0% (4/20) and 13.0% (6/46) in the 2013 and 2014 surveys, respectively. More than 95% of veterinary students had received the mandatory Q fever vaccine. Both veterinarians and students regarded bats and horses as high-risk species for zoonoses.

CONCLUSIONS

Queensland veterinarians and veterinary students have low levels of protection against ABLV. Although incidents of ABLV spilling over from a bat to a domestic mammal are likely to remain rare, they pose a significant human health and occupational risk given the outcome of infection in humans is high consequence. Principals of veterinary practices and veterinary authorities in Australia should implement a policy of rabies vaccination for clinical staff and veterinary students.

Rabies antibody response after two intradermal pre-exposure prophylaxis immunizations: An observational cohort study

BACKGROUND

Rabies is a lethal, but vaccine preventable disease. Vaccination uptake is however hampered by the time-consuming three-dose, 21/28-day schedule. The aim of this study was to examine whether adequate rabies antibody titers are reached after two intradermal (ID) doses of rabies vaccine, with a seven-day window.

METHOD

We conducted an observational cohort study with military personnel. A titer was assessed by RFFIT, on the day of the third vaccination, to ensure an adequate rabies antibody response after ID immunization.

RESULTS

After this abbreviated two-dose, seven-day ID schedule, seroconversion was reached in 99.3% (427/430) with a geometric mean titer of 7.59 IU/mL (95% CI 7.04-8.17).

CONCLUSIONS

Implementation of this two-dose schedule will protect more people against Rabies. Travelers and military personnel under time constraints, who otherwise would remain unvaccinated, can be considered adequately protected after this two-dose schedule. For populations in endemic areas, local application of a two-dose schedule could provide an opportunity to vaccinate more people with less vaccine. Given the paucity of published data, this study adds relevant evidence in support of the new policy (2017) of WHO, concerning a two-dose, seven-day schedule is approved for all healthy individuals.

Intradermal pre-exposure rabies vaccination in a Canadian travel clinic: 6-year retrospective observational study

BACKGROUND

The intradermal route of vaccine administration for pre-exposure rabies prophylaxis, endorsed by the Canadian National Advisory Committee on Immunization, was implemented at a large travel clinic in Montréal in 2008. We evaluated the effect of intradermal vaccination availability on uptake of pre-exposure rabies prophylaxis and rates of seroconversion with intradermal vaccination.

METHODS

We conducted a retrospective cross-sectional study using data from December 2008 to December 2014. The number of travellers who received pre-exposure rabies prophylaxis before and after the introduction of intradermal vaccination was compared. Postvaccination antibody titres were measured in intradermal vaccination recipients. We compared demographic and travel characteristics between vaccinated and unvaccinated travellers and between travellers in the intradermal and intramuscular groups using univariate and multivariate analyses.

RESULTS

The proportion of travellers who received pre-exposure prophylaxis increased after the introduction of intradermal vaccination (annual average of 300 travellers from December 2009 to December 2014 v. 183 travellers from December 2006 to December 2007). Seroconversion occurred in 99.9% of those in the intradermal group. Travellers who received pre-exposure prophylaxis were older (mean age 35.8 yr v. 32.1 yr) and had longer travel duration than those who did not receive pre-exposure prophylaxis. Travellers to Asia were more likely to receive pre-exposure prophylaxis, and travellers visiting friends and relatives were less likely to receive it. Travellers in the intradermal group were younger than those in the intramuscular group and were more likely to be travelling for tourism.

INTERPRETATION

The introduction of intradermal vaccination for pre-exposure rabies prophylaxis was associated with an increase in vaccination uptake. Reduced cost may be responsible for the increased coverage among younger travellers and those travelling for tourism. The high seroconversion rate after intradermal vaccination supports the effectiveness of this route of administration for pre-exposure rabies prophylaxis in immunocompetent people.

Single visit rabies pre-exposure priming induces a robust anamnestic antibody response after simulated post-exposure vaccination: results of a dose-finding study

BACKGROUND

The current standard 3-dose intramuscular rabies PrEP schedule suffers from a number of disadvantages that severely limit accessibility and availability. The cost of is often prohibitive, it requires 3 visits to the clinic, and there are regular vaccine shortages.

METHODS

Volunteers ( N  = 30) were randomly assigned to 4 study arms: 1 standard dose intramuscular (IM) dose of PVRV (purified Vero cell rabies vaccine, Verorab), and 1/5th, 2/5th or 3/5th- fractional intradermal (ID) dose of PVRV in a single visit. All subjects received a simulated rabies post-exposure prophylaxis (D0, D3) 1 year later. Rabies virus neutralizing antibodies (RVNA) were determined by virus neutralization microtest (FAVN) on D0, D7, D28, Y1 and Y1 + D7.

RESULTS

28 out of 30 subjects (93%) seroconverted 1 month after primary vaccination; 1 subject in the 1-dose IM arm and 1 in the 1/5th-fractional dose ID arm did not. After 1 year, 22 out of 30 subjects (73%) no longer had RVNA above 0.5 IU/ml, with no discernible difference between study groups. After 1 year, all 30 subjects mounted a booster response within 7 days after simulated PEP, with the highest titers found in the single dose IM group ( P  < 0.03).

CONCLUSIONS

This dose finding study demonstrates that priming with a single dose of rabies vaccine was sufficient to induce an adequate anamnestic antibody response to rabies PEP in all subjects 1 year later, even in those in whom the RVNA threshold of 0.5 IU/ml was not reached after priming.

Guidelines for the prevention of travel-associated illness in older adults

International travel to the developing world is becoming more common in elderly patients (defined here as individuals greater than 65 years old). When providing pre-travel counseling, providers must appreciate the changing physiology, comorbidities, immunity and pharmacokinetics associated with the aging process to prepare elderly patients for the stressors of international travel. These guidelines present an evidence-based approach to pre-travel counseling, immunization, and pharmacology concerns unique to elderly patients seeking care in a travel clinic setting.

Pre-exposure rabies prophylaxis: a systematic review

OBJECTIVE

To review the safety and immunogenicity of pre-exposure rabies prophylaxis (including accelerated schedules, co-administration with other vaccines and booster doses), its cost-effectiveness and recommendations for use, particularly in high-risk settings.

METHODS

We searched the PubMed, Centre for Agriculture and Biosciences International, Cochrane Library and Web of Science databases for papers on pre-exposure rabies prophylaxis published between 2007 and 29 January 2016. We reviewed field data from pre-exposure prophylaxis campaigns in Peru and the Philippines.

FINDINGS

Pre-exposure rabies prophylaxis was safe and immunogenic in children and adults, also when co-administered with routine childhood vaccinations and the Japanese encephalitis vaccine. The evidence available indicates that shorter regimens and regimens involving fewer doses are safe and immunogenic and that booster intervals could be extended up to 10 years. The few studies on cost suggest that, at current vaccine and delivery costs, pre-exposure prophylaxis campaigns would not be cost-effective in most situations. Although pre-exposure prophylaxis has been advocated for high-risk populations, only Peru and the Philippines have implemented appropriate national programmes. In the future, accelerated regimens and novel vaccines could simplify delivery and increase affordability.

CONCLUSION

Pre-exposure rabies prophylaxis is safe and immunogenic and should be considered: (i) where access to postexposure prophylaxis is limited or delayed; (ii) where the risk of exposure is high and may go unrecognized; and (iii) where controlling rabies in the animal reservoir is difficult. Pre-exposure prophylaxis should not distract from canine vaccination efforts, provision of postexposure prophylaxis or education to increase rabies awareness in local communities.

An update on the use of laser technology in skin vaccination

Vaccination via skin often induces stronger immune responses than via muscle. This, in line with potential needle-free, painless delivery, makes skin a very attractive site for immunization. Yet, despite decades of effort, effective skin delivery is still in its infant stage and safe and potent adjuvants for skin vaccination remain largely undefined. We have shown that laser technologies including both fractional and non-fractional lasers can greatly augment vaccine-induced immune response without incurring any significant local and systemic side effects. Laser illumination at specific settings can accelerate the motility of antigen-presenting cells or trigger release of 'danger' signals stimulating the immune system. Moreover, several other groups including the authors explore laser technologies for needle-free transcutaneous vaccine delivery. As these laser-mediated resurfacing technologies are convenient, safe and cost-effective, their new applications in vaccination warrant clinical studies in the very near future.

Travel and non-travel associated rabies post exposure treatment in New South Wales residents, Australia, 2007-2011: a cross-sectional analysis

BACKGROUND

Australian Bat Lyssavirus is endemic in Australian bats. More Australians are travelling to rabies (Lyssavirus 1) endemic countries. The nature and frequency of lyssavirus exposures and characteristics of New South Wales (NSW) residents exposed have not previously been described.

METHOD

Access to free rabies post-exposure treatment (PET) can only be arranged through Public Health Units in NSW. Details of people receiving PET after potential exposures to rabies or ABLV from 1 January 2007 to 31 December 2011 were extracted from an NSW Ministry of Health web-based database and analysed to better understand lyssavirus exposure epidemiology.

RESULTS

Of 1195 people receiving PET, 415 exposures were in Australia and 780 abroad; 78.3% occurring in Southeast Asia, mainly Indonesia (47.6%) where most were on the island of Bali (95.2%). PET use increased substantially for domestic and international exposures. In Australia, most bat exposures were to members of the public (76.0%), rather than to people who work with bats professionally or as volunteers, with 54.1% due to bat rescue attempts. Injuries abroad were mainly from monkeys (49.4%) and from dogs (35.8%). Only 4.0% of international travellers were vaccinated prior to their exposure.

CONCLUSIONS

Increasing rates of PET in travelling and non-travelling Australians emphasise the need for more effective communication about appropriate animal avoidance and the measures required if exposed. Opportunities for increasing pre-exposure treatment amongst individuals likely to be exposed should be promoted.

Expatriates: special considerations in pretravel preparation

Expatriates comprise a diverse set of travelers who face unique medical, psychiatric, and non-health-related risks as a result of increased exposure to host country environment and associated lifestyle. Expatriates have an increased risk of developing malaria, gastrointestinal disorders, latent tuberculosis, vaccine-preventable infections, and psychological disorders, when compared with other travelers, yet the majority of existing pretravel guidelines have been designed to suit the needs of nonexpatriates. Although greater interest in expatriate health issues has led to improved characterization of illness in this population, expatriate-specific risk mitigation strategies-including modifications to chemoprophylaxis recommendations, limiting tuberculosis exposure, and prevention of occupational or sexual blood-borne virus transmission-are poorly described. Occupations and destinations affect travel-related disease risk and should inform the pretravel consultation.

Rabies vaccination for international travelers

Rabies prevention in travelers is a controversial issue. According to experts, the decision to vaccinate results from an individual risk assessment based on the duration of stay, the likelihood of engagement in at-risk activities, the age of the traveler, the rabies endemicity and access to appropriate medical care in the country of destination. However, no detailed information is available regarding the last two determinants in many regions. Twenty-two cases of rabies were reported in tourists, expatriates and migrant travelers over the last decade, including three cases following short-term travel of no more than two weeks. Studies on rabies post-exposure prophylaxis (PEP) in travelers show that overall, 0.4% (range 0.01-2.3%) of travelers have experienced an at-risk bite per month of stay in a rabies-endemic country, while 31% of expatriates and 12% of tourists were vaccinated against rabies before traveling. The main reason cited by travelers for not being vaccinated is the cost of the vaccine. The majority of patients who sustained a high risk injury was not vaccinated against rabies before traveling and were not properly treated abroad. From available studies, the following risk factors for injuries sustained from potentially rabid animals may be identified: traveling to South-East Asia, India or North Africa, young age, and traveling for tourism. The duration of travel does not appear to be a risk factor. It should be noted that "at-risk activities" have not been addressed in these studies. Detailed rabies distribution maps and information on the availability of rabies biologics are urgently needed in order to identify those travelers who need pre-travel vaccination. Meanwhile, cost-minimization of rabies pre-exposure vaccination may be achieved in several ways, notably by using the intra-dermal method of vaccination.