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

Real-world evidence of rabies post-exposure prophylaxis in Serbia: Nation-wide observational study (2017-2019)

BACKGROUND

Rabies remains a deadly zoonotic disease, primarily prevalent in Eastern European countries, with a significant global burden in Asia and Africa. Post-exposure prophylaxis (PEP) is critical to prevent clinical rabies. Serbia, a country with a relatively low animal rabies incidence, has been implementing a 4-dose Essen PEP regimen for 13 years. This real-world study aimed to assess the effectiveness of the 4-dose Essen regimen, considering demographic and clinical factors, after WHO Category III exposure.

METHOD

The study included 601 patients who received the 4-dose Essen PEP and 79 who received an additional 5th dose.

RESULTS

Age emerged as a critical factor influencing seroconversion rates after the 4-dose regimen, with older individuals exhibiting lower RVNA titers. Logistic regression indicated a 3.18% decrease in seroconversion odds for each added year of age. The Cox proportional hazards mixed model highlighted age-related risks, with age groups 45-60 and 75-92 at the highest risk of non-seroconversion. Human Rabies Immune Globulin (HRIG) administration was associated with lower RVNA values after the 4-dose regimen, suggesting interference with vaccine immunogenicity among people who received larger doses of HRIG.

CONCLUSIONS

This study provides valuable real-world evidence for rabies PEP in a non-homogeneous population with potential comorbidities. The results underscore the importance of optimizing PEP strategies, particularly in older individuals, and reconsidering HRIG dosing to improve seroconversion rates.

Boostability after single-visit pre-exposure prophylaxis with rabies vaccine: a randomised controlled non-inferiority trial

BACKGROUND

After rabies pre-exposure prophylaxis (PrEP) vaccination, scarcely available rabies immunoglobulins are not required for post-exposure prophylaxis (PEP). However, PrEP is not sufficiently accessible as it is cost-intensive and time-intensive. This study investigates whether rabies PrEP schedules can be shortened to one visit, removing some of these barriers.

METHODS

In a block-randomised (2:2:2:1) controlled, multicentre non-inferiority trial, healthy adult travellers (aged 18-50 years and >50 years) were randomly assigned to (A) single-visit intramuscular (1·0 mL); (B) single-visit intradermal (0·2 mL); (C) standard two-visit intramuscular (1·0 mL; day 0 and 7) PrEP; or (D) no rabies vaccination. 6 months later, participants received simulated intramuscular rabies PEP (1·0 mL; day 0 and 3). Rabies virus neutralising antibody (RVNA) concentrations were measured repeatedly. The primary outcome was the fold increase in geometric mean RVNA concentrations between day 0 and 7 after simulated PEP for all participants. The two main comparisons of this primary outcome are between the standard two-visit schedule and the one-visit intramuscular schedule, and between the standard two-visit schedule and the one-visit intradermal schedule. The non-inferiority margin was 0·67. This study is registered with EudraCT, 2017-000089-31.

FINDINGS

Between May 16, 2018, and March 26, 2020, 288 healthy adult travellers were randomly assigned and 214 participants were evaluated for the primary outcome. Single-visit intramuscular rabies PrEP induced an anamnestic antibody response non-inferior compared with the two-visit intramuscular schedule; single-visit intradermal PrEP did not. The fold increases in the single-visit intramuscular and the single-visit intradermal schedule were 2·32 (95% CI [1·43-3·77]) and 1·11 (0·66-1·87) times as high as the fold increase in the standard schedule, respectively. No vaccine-related serious adverse events were observed. Adverse events related to vaccination were mostly mild.

INTERPRETATION

Single intramuscular rabies vaccination can effectively prime travellers (aged 18-50 years), and potentially other populations, and could replace current standard two-visit rabies vaccination as PrEP.

FUNDING

ZonMW.

TRANSLATION

For the Dutch translation of the abstract see Supplementary Materials section.

Single visit rabies pre-exposure prophylaxis: A literature review

BACKGROUND

The current WHO-recommended rabies pre-exposure prophylaxis (PrEP) are two-visit vaccination schedules, but there are studies suggesting that single visit schedules might be sufficient to prime the immunity.

METHODS

A literature review was conducted to retrieve and summarize published data on single visit rabies PrEP. PubMed database was screened for articles published between January 1st, 2003 and December 31st, 2022. The bibliographies of the articles chosen to undergo full text review and of the current major WHO publications on rabies were searched to find additional references, regardless of publication date. The primary outcome was the percentage of subjects having received rabies PrEP on single visit schedules who achieved antibody levels ≥0.5 IU/mL one week after post-exposure prophylaxis (PEP), regardless of the PEP regimen.

RESULTS

11 studies were selected for inclusion, totalling 935 subjects, of which 696 received a simulated PEP schedule. Of these 696, a serological test result on day 7 was available for 408 of them, and 406 subjects (99.51%) seroconverted after PEP without any difference regarding time delay between PrEP and PEP or the vaccination schedule used for PEP.

CONCLUSION

Single visit PrEP schedules seem to confer sufficient protection in most healthy individuals without immunocompromised status if a booster PEP is administered after a suspected rabies exposure. Further studies in real-life settings and in different age categories are needed to confirm this finding, which may increase the availability of vaccines and thus the accessibility of PrEP for vulnerable populations.

Safety and immunogenicity of a simian-adenovirus-vectored rabies vaccine: an open-label, non-randomised, dose-escalation, first-in-human, single-centre, phase 1 clinical trial

BACKGROUND

Rabies kills around 60 000 people each year. ChAdOx2 RabG, a simian adenovirus-vectored rabies vaccine candidate, might have potential to provide low-cost single-dose pre-exposure rabies prophylaxis. This first-in-human study aimed to evaluate its safety and immunogenicity in healthy adults.

METHODS

We did a single-centre phase 1 study of ChAdOx2 RabG, administered as a single intramuscular dose, with non-randomised open-label dose escalation at the Centre for Clinical Vaccinology and Tropical Medicine, Oxford, UK. Healthy adults were sequentially allocated to groups receiving low (5 × 109 viral particles), middle (2·5 × 1010 viral particles), and high doses (5 x 1010 viral particles) of ChAdOx2 RabG and were followed up to day 56 after vaccination. The primary objective was to assess safety. The secondary objective was to assess immunogenicity with the internationally standardised rabies virus neutralising antibody assay. In an optional follow-up phase 1 year after enrolment, we measured antibody maintenance then administered a licensed rabies vaccine (to simulate post-exposure prophylaxis) and measured recall responses. The trial is registered with ClinicalTrials.gov, NCT04162600, and is now closed to new participants.

FINDINGS

Between Jan 2 and Oct 28, 2020, 12 adults received low (n=3), middle (n=3), and high doses (n=6) of ChAdOx2 RabG. Participants reported predominantly mild-to-moderate reactogenicity. There were no serious adverse events. Virus neutralising antibody concentrations exceeded the recognised correlate of protection (0·5 IU/mL) in three middle-dose recipients and six high-dose recipients within 56 days of vaccination (median 18·0 IU/mL). The median peak virus neutralising antibody concentrations within 56 days were 0·7 IU/mL (range 0·0-54·0 IU/mL) for the low-dose group, 18·0 IU/mL (0·7-18·0 IU/mL) for the middle-dose group, and 18·0 IU/mL (6·0-486·0 IU/mL) for the high-dose group. Nine participants returned for the additional follow-up after 1 year. Of these nine participants, virus neutralising antibody titres of more than 0·5 IU/mL were maintained in six of seven who had received middle-dose or high-dose ChAdOx2 RabG. Within 7 days of administration of the first dose of a licensed rabies vaccine, nine participants had virus neutralising antibody titres of more than 0·5 IU/mL.

INTERPRETATION

In this study, ChAdOx2 RabG showed an acceptable safety and tolerability profile and encouraging immunogenicity, supporting further clinical evaluation.

FUNDING

UK Medical Research Council and Engineering and Physical Sciences Research Council.

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.

Two-year immunogenicity of a pre-exposure rabies vaccination administered as a two-dose schedule

In a young and healthy population, immunogenicity at 2 years of a rabies pre-exposure prophylaxis in a two-dose intramuscular schedule is satisfying. This regimen may be appropriate in people occupationally exposed to RABV, or travelling to highly endemic countries, provided they receive two booster doses in case of exposure.

Immunogenicity of 2-dose pre-exposure rabies vaccine co-administered with quadrivalent influenza vaccine in children

OBJECTIVES

The World Health Organization recommends a 2-dose rabies pre-exposure prophylaxis (PrEP) regimen. This study aimed to compare the immunogenicity of rabies PrEP regimens co-administered with inactivated quadrivalent influenza vaccine (IIV4).

METHODS

Children aged 3 to 9 years were randomly assigned (2:2:1) to receive 0.25 mL of chromatographically purified Vero cell rabies vaccine intramuscularly: Group A at day 0, 7 with IIV4; Group B at day 0, 28 with IIV4; Group C at day 0, 7. A booster-dose of CPRV was given on day 365. Primary outcome was the proportion of children with protective rabies virus neutralizing antibody (RVNA) ≥ 0.5 IU/mL, on day 42 and 7 days post-booster.

RESULTS

From November 2019 to January 2020; 100 children with a median age (IQR) of 5.4 years (4.8-7.3) were enrolled. All participants achieved protective RVNA titers on day 42 and 7-days post booster. Geometric mean titers (GMT) at day 42 were Group A, 8.98(95%CI 7.06-11.42); Group B, 23.89(95%CI 19.33-29.51); Group C, 9.94(95%CI 7.03-14.06). Likewise, RVNA GMT at 7 days post-booster were Group A, 42.53(95%CI 18.41-66.64); Group B, 23.19(95%CI 17.28-29.10); Group C, 57.75 (95%CI 35.86-79.67).

CONCLUSIONS

The 2-dose PrEP regimen of rabies vaccine produces adequate immune response either 0,7 or 0, 28 regimens.

Hematobiochemical and Immunological Responses of Rats Treated with Multi-strain Probiotics and Infected with Trypanosoma brucei

The effects of treatment with probiotics on the immunological and hematobiochemical changes in Trypanosoma brucei infection were investigated. Probiotic strains used are Bifidobacterium BB-12, Lactobacillus acidophilus LA-5, Lactobacillus delbrueckii LBY-27, Lactobacillus paracasei LC-01, and Streptococcus thermophilus STY-31. Thirty rats randomly assigned to five groups were used in the experiment. Groups A to C received 1 × 10⁹ CFU, 5 × 10⁹ CFU, and 10 × 10⁹ CFU of the multi-strain probiotics daily and respectively from day 0 post-supplementation (PS) to termination. Group D and E were the infected and uninfected controls respectively. On day seven PS, groups A to D were challenged intraperitoneally with approximately 1 × 10⁶ trypanosomes. Parasitemia, nitric oxide level, hematobiochemical parameters, and antibody titer to heterologous antigen stimulation were monitored post-infection. By days 7 and 16 PS, probiotics-treated groups had significantly lower (p < 0.05) mean creatinine concentration than the controls; however, on day 7 PS, there were no significant variations in the leukocyte counts (LC), total erythrocyte counts (TEC), and the packed cell volume (PCV) in all experimental groups. Following infection, by day 16 PS, the pre-patent period, parasitemia levels, and antibody titer were similar in all infected groups. Furthermore, the probiotics-treated groups and the infected control had significantly lower PCV, TEC, and LC values when compared to the uninfected control, and probiotics treated groups (A and C) had only marginally lower nitric oxide levels than the infected control. Treatment with the probiotic strains gave a creatinine-lowering effect, was innocuous to the hematopoietic system, but was not sufficiently immunostimulatory in trypanosomosis.

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.

Long-term memory response after a single intramuscular rabies booster vaccination, 10-24 years after primary immunization

BACKGROUND

To date, published data regarding long-lasting immunological rabies memory after a pre-exposure prophylaxis (PrEP)-schedule are scarce. We tested the hypothesis that rabies booster immunization elicits rapid anamnestic responses.

METHODS

For this observational study, we included participants who had received PrEP 10-24 years before inclusion. We measured rabies antibody titers before, and on days 3, 7 and 14 after one single intramuscular booster.

RESULTS

All 28 participants responded adequately regardless route of administration or (2-dose vs. 3-dose) PrEP-regimen.

CONCLUSION

Rabies immunological memory is reactivated within 7 days after a single intramuscular booster immunization, even when administered 10-24 years after PrEP.

Investigating the Interaction between Negative Strand RNA Viruses and Their Hosts for Enhanced Vaccine Development and Production

The current pandemic has highlighted the ever-increasing risk of human to human spread of zoonotic pathogens. A number of medically-relevant zoonotic pathogens are negative-strand RNA viruses (NSVs). NSVs are derived from different virus families. Examples like Ebola are known for causing severe symptoms and high mortality rates. Some, like influenza, are known for their ease of person-to-person transmission and lack of pre-existing immunity, enabling rapid spread across many countries around the globe. Containment of outbreaks of NSVs can be difficult owing to their unpredictability and the absence of effective control measures, such as vaccines and antiviral therapeutics. In addition, there remains a lack of essential knowledge of the host–pathogen response that are induced by NSVs, particularly of the immune responses that provide protection. Vaccines are the most effective method for preventing infectious diseases. In fact, in the event of a pandemic, appropriate vaccine design and speed of vaccine supply is the most critical factor in protecting the population, as vaccination is the only sustainable defense. Vaccines need to be safe, efficient, and cost-effective, which is influenced by our understanding of the host–pathogen interface. Additionally, some of the major challenges of vaccines are the establishment of a long-lasting immunity offering cross protection to emerging strains. Although many NSVs are controlled through immunisations, for some, vaccine design has failed or efficacy has proven unreliable. The key behind designing a successful vaccine is understanding the host–pathogen interaction and the host immune response towards NSVs. In this paper, we review the recent research in vaccine design against NSVs and explore the immune responses induced by these viruses. The generation of a robust and integrated approach to development capability and vaccine manufacture can collaboratively support the management of outbreaking NSV disease health risks.

Redefining Non-Inferiority in Anamnestic Antibody Responses Using the Mean Increase of Log-Transformed Antibody Titers after Revaccination: Secondary Analysis of a Randomized Controlled Rabies Vaccination Trial

Non-inferiority in the anamnestic antibody response is conventionally determined by comparing seroconversion rates after revaccination. However, this approach is inadequate in the case of high pre-booster antibody titers. Therefore, we propose an alternative method to determine non-inferiority of booster responses. We used anonymized data from a randomized controlled trial (NCT01388985; EudraCT 2011-001612-62) in 500 adults, comparing a two-visit primary vaccination schedule (two intradermal 0.1 mL rabies vaccine doses on day 0 and 7) with a three-visit schedule (single intradermal 0.1 mL dose on day 0, 7, and 28). Participants were revaccinated intradermally (single dose) 1 to 3 years later. Rabies virus neutralizing antibody titers were measured on day 0 and 7 after revaccination. After log₃-transformation of antibody titers, the mean increase in titers after revaccination was compared between schedules. Non-inferiority was defined as the lower bound of the two-sided 95% confidence interval not exceeding -0.369. Four hundred and ten participants fulfilled the inclusion criteria. The mean increase in log₃ titer was 2.21 and 2.31 for the two-visit and three-visit schedule, respectively. The difference between these increases was -0.10 [-0.28, 0.08], meeting the non-inferiority criterion. In conclusion, comparing mean increases in log-transformed titers after revaccination appears to be a feasible and more informative method of studying non-inferiority regarding the anamnestic antibody response.

Rabies exposure in travellers to Asia, the Middle East, Africa, South and Central America-a German Airport study

BACKGROUND

Rabies causes thousands of deaths worldwide and trips to rabies endemic countries are popular. Travellers are often uncertain whether pre-exposure prophylaxis (PrEP) is advisable since they find it difficult to estimate the exposure risk during travel and the availability of post-exposure prophylaxis in endemic regions. The aim of this study was to determine the potential rabies exposures in travellers and to assess their knowledge on rabies. Secondly, we explored the access to appropriate post-exposure medical care in respective countries.

METHODS

We conducted a cross-sectional study at Frankfurt Airport. Returning adult travellers arriving from Asia, the Middle East, Africa, South and Central America were invited to participate in this questionnaire-based study while waiting in the baggage claim area.

RESULTS

Over a one-month recruitment phase in March 2019, we enrolled 3066 travellers; 2929 were included in the analysis. The gender ratio was balanced; the median age was 42 years (range 18-83 years). Participants arrived from Asia (46%), Africa (29%), Central/South America (13%), the Middle East (8%) and the Caribbean (8%). Forty-five per cent sought pretravel advice and 22% received ≥2 injections of rabies PrEP. Travellers with pretravel advice from tropical medicine specialists reached significantly higher knowledge scores than others. We found that potential rabies exposure occurred in 2.0% (57/2915) of travellers with 31% (13/42) of the contacts being unprovoked; 19% (8/42) of the exposed sought medical care and 3/8 were adequately treated before returning to Germany. Risk factors for animal exposure were: male sex, young age, trips to Asia and a long stay abroad (>4 weeks).

CONCLUSIONS

A total of 2% of returning travellers (n = 2915) experienced a potential rabies exposure during their journey. A majority of the exposed individuals did not seek medical care; those seeking medical care were often treated inadequately. Rabies information must be emphasised during pretravel counselling and PrEP should be offered generously, especially to travellers with high exposure risks.

Rabies vaccination strategies in the Netherlands in 2018: a cost evaluation

BackgroundThe risk of contracting rabies is low for travellers. However, the number of Dutch travellers potentially exposed abroad following an animal-associated injury and needing post-exposure prophylaxis (PEP) has increased, resulting in increased costs.AimHere, we evaluated the costs and the cost-effectiveness of different pre- and post-exposure interventions in the Netherlands, taking into account the 2018 World Health Organization (WHO) recommendations for the prevention of rabies.MethodsA decision tree-based economic model was constructed. We calculated and compared the cost of different WHO pre-exposure prophylaxis (PrEP) recommendations, intramuscular vs intradermal vaccination and PEP subsequent to increased vaccination coverage in risk groups. We estimated cost-effectiveness, expressed as incremental costs per rabies immunoglobulin (RIG) administration averted, using a societal perspective. Statistical uncertainty regarding number of travellers and vaccination coverage was assessed.ResultsTotal costs at the national level were highest using previous WHO recommendations from 2012, estimated at EUR 15.4 million annually. Intradermal vaccinations in combination with the current recommendations led to the lowest costs, estimated at EUR 10.3 million. Higher vaccination uptake resulted in higher overall costs. The incremental costs per RIG administration averted varied from EUR 21,300-46,800.ConclusionsThe change in rabies PrEP and PEP recommendations in 2018 reduced total costs. Strategies with increased pre-travel vaccination uptake led to fewer RIG administrations and fewer vaccinations after exposure but also to higher total costs. Although larger scale intradermal administration of rabies vaccine can reduce total costs of PrEP and can positively influence vaccination uptake, it remains a costly intervention.

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.

Fractional dose of intradermal compared to intramuscular and subcutaneous vaccination - A systematic review and meta-analysis

BACKGROUND

Vaccine supply shortages are of global concern. We hypothesise that intradermal (ID) immunisation as an alternative to standard routes might augment vaccine supply utilisation without loss of vaccine immunogenicity and efficacy.

METHODS

We conducted a systematic review and meta-analysis searching Medline, Embase and Web of Science databases. Studies were included if: licensed, currently available vaccines were used; fractional dose of ID was compared to IM or SC immunisation; primary immunisation schedules were evaluated; immunogenicity, safety data and/or cost were reported. We calculated risk differences (RD). Studies were included in meta-analysis if: a pre-defined immune correlate of protection was assessed; WHO-recommend schedules and antigen doses were used in the control group; the same schedule was applied to both ID and control groups (PROSPERO registration no. CRD42020151725).

RESULTS

The primary search yielded 5,873 articles, of which 156 articles were included; covering 12 vaccines. Non-inferiority of immunogenicity with 20-60% of antigen used with ID vaccines was demonstrated for influenza (H1N1: RD -0·01; 95% CI -0·02, 0·01; I² = 55%, H2N3: RD 0·00; 95% CI -0·01, 0·01; I² = 0%, B: RD -0·00; 95% CI -0·02, 0·01; I² = 72%), rabies (RD 0·00; 95% CI -0·02, 0·02; I² = 0%), and hepatitis B vaccines (RD -0·01; 95% CI -0·04, 0·02; I² = 20%). Clinical trials on the remaining vaccines yielded promising results, but are scarce.

CONCLUSIONS

There is potential for inoculum/antigen dose-reduction by using ID immunisation as compared to standard routes of administration for some vaccines (e.g. influenza, rabies). When suitable, vaccine trials should include an ID arm.

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.

Purified Vero Cell Rabies Vaccine (PVRV, Verorab®): A Systematic Review of Intradermal Use Between 1985 and 2019

The purified Vero cell rabies vaccine (PVRV; Verorab®, Sanofi Pasteur) has been used in rabies prevention since 1985. Evolving rabies vaccination trends, including shorter intradermal (ID) regimens with reduced volume, along with WHO recommendation for ID administration has driven recent ID PVRV regimen assessments. Thus, a consolidated review comparing immunogenicity of PVRV ID regimens during pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP) is timely and beneficial in identifying gaps in current research. A search of seven databases for studies published from 1985 to November 2019 identified 35 studies. PrEP was assessed in 10 studies (n = 926) with 1-3-site, 1-3-visit regimens of up to 3-months duration. Seroconversion (rabies virus neutralizing antibodies [RVNA] ≥ 0.5 IU/mL) rates of 90-100% were reported within weeks, irrespective of regimen, with robust booster responses at 1 year (100% seroconversion rates by day 14 post-booster). However, data are lacking for the current WHO-recommended, 2-site, 1-week ID PrEP regimen. PEP was assessed in 25 studies (n = 2136) across regimens of 1-week to 90-day duration. All ID PEP regimens assessed induced ≥ 99% seroconversion rates (except in HIV participants) by day 14-28. This review confirms ID PVRV suitability for rabies prophylaxis and highlights the heterogeneity of use in the field.

Vaccines for International Travel

The pretravel management of the international traveler should be based on risk management principles. Prevention strategies and medical interventions should be based on the itinerary, preexisting health factors, and behaviors that are unique to the traveler. A structured approach to the patient interaction provides a general framework for an efficient consultation. Vaccine-preventable diseases play an important role in travel-related illnesses, and their impact is not restricted to exotic diseases in developing countries. Therefore, an immunization encounter before travel is an ideal time to update all age-appropriate immunizations as well as providing protection against diseases that pose additional risk to travelers that may be delineated by their destinations or activities. This review focuses on indications for each travel-related vaccine together with a structured synthesis and graphics that show the geographic distribution of major travel-related diseases and highlight particularly high-risk destinations and behaviors. Dosing, route of administration, need for boosters, and possible accelerated regimens for vaccines administered prior to travel are presented. Different underlying illnesses and medications produce different levels of immunocompromise, and there is much unknown in this discipline. Recommendations regarding vaccination of immunocompromised travelers have less of an evidence base than for other categories of travelers. The review presents a structured synthesis of issues pertinent to considerations for 5 special populations of traveler: child traveler, pregnant traveler, severely immunocompromised traveler, HIV-infected traveler, and traveler with other chronic underlying disease including asplenia, diabetes, and chronic liver disease.

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.

An overview of the immunogenicity and effectiveness of current human rabies vaccines administered by intradermal route

Pre- as well as post-exposure prophylaxis plays an important role in controlling the number of deaths associated with human rabies. Rabies vaccines, classically injected intramuscularly, are now also administered by intradermal (ID) route. Vaccines to be administered by the ID route should meet the same quality, safety and efficacy specifications as vaccines for intramuscular (IM) use. The aim of this paper is to provide information based on publicly available data regarding the ID use of rabies vaccines and to identify potential needs for further analysis of the potency, immunogenicity and effectiveness of rabies vaccines administered by this route. A first literature search, focused on the immunogenicity of rabies vaccines given by ID route, identified 338 publications in the period 1997-2018, 40 of which were included in our analyses. A second search investigating the effectiveness of ID vaccination resulted in 371 hits for the period 2007-2018, of which 13 suitable publications were retained. The immunogenicity of current rabies vaccines was analyzed in 3 ways: proportion of subjects reaching the antibody threshold of 0.5 IU/ml after ID vaccination, relationship between potency and immunogenicity of the vaccine given intradermally, and comparison of antibody responses after IM or ID vaccination. Overall, vaccines administered intradermally were found immunogenic. Post-exposure prophylaxis by ID route appeared at least as immunogenic as by IM regimens. By contrast, ID pre-exposure prophylaxis trended towards lower antibody titers than IM vaccination, but the observation was not associated with any clinical relevance. Vaccine effectiveness was assessed by investigating survival after exposure. Data from more than 30,000 patients who sought rabies post-exposure prophylaxis did not indicate that current vaccines administered by ID route lack efficacy. These results support current recommendations for ID vaccination against rabies. However, published data on ID performance were associated with significant weaknesses that future research should better address.

A simian-adenovirus-vectored rabies vaccine suitable for thermostabilisation and clinical development for low-cost single-dose pre-exposure prophylaxis

BACKGROUND

Estimates of current global rabies mortality range from 26,000 to 59,000 deaths per annum. Although pre-exposure prophylaxis using inactivated rabies virus vaccines (IRVs) is effective, it requires two to three doses and is regarded as being too expensive and impractical for inclusion in routine childhood immunization programmes.

METHODOLOGY/ PRINCIPAL FINDINGS

Here we report the development of a simian-adenovirus-vectored rabies vaccine intended to enable cost-effective population-wide pre-exposure prophylaxis against rabies. ChAdOx2 RabG uses the chimpanzee adenovirus serotype 68 (AdC68) backbone previously shown to achieve pre-exposure protection against rabies in non-human primates. ChAdOx2 differs from AdC68 in that it contains the human adenovirus serotype 5 (AdHu5) E4 orf6/7 region in place of the AdC68 equivalents, enhancing ease of manufacturing in cell lines which provide AdHu5 E1 proteins in trans. We show that immunogenicity of ChAdOx2 RabG in mice is comparable to that of AdC68 RabG and other adenovirus serotypes expressing rabies virus glycoprotein. High titers of rabies virus neutralizing antibody (VNA) are elicited after a single dose. The relationship between levels of VNA activity and rabies virus glycoprotein monomer-binding antibody differs after immunization with adenovirus-vectored vaccines and IRV vaccines, suggesting routes to further enhancement of the efficacy of the adenovirus-vectored candidates. We also demonstrate that ChAdOx2 RabG can be thermostabilised using a low-cost method suitable for clinical bio-manufacture and ambient-temperature distribution in tropical climates. Finally, we show that a dose-sparing effect can be achieved by formulating ChAdOx2 RabG with a simple chemical adjuvant. This approach could lower the cost of ChAdOx2 RabG and other adenovirus-vectored vaccines.

CONCLUSIONS/ SIGNIFICANCE

ChAdOx2 RabG may prove to be a useful tool to reduce the human rabies death toll. We have secured funding for Good Manufacturing Practice- compliant bio-manufacture and Phase I clinical trial of this candidate.

Safety and immunogenicity of fractional dose intradermal injection of two quadrivalent conjugated meningococcal vaccines

BACKGROUND

Vaccination with conjugated meningococcal vaccines is the best way to prevent invasive meningococcal disease. Changes in serogroup epidemiology have led to the inclusion of quadrivalent vaccines in the national immunization programs of several countries, but vaccines are frequently in short supply. Intradermal administration has the potential to increase vaccine availability through dose reduction, without sacrificing efficacy. It has never before been investigated for glycoconjugate meningococcal vaccines.

METHODS

Different fractional doses of two quadrivalent meningococcal conjugate vaccines (MenACWY-CRM₁₉₇ (Menveo®) and MenACWY-TT (Nimenrix®)) were administered intradermally to sequential groups of 4 participants, according to an adaptive dose escalation design, starting at 1/10th of the original dose. Booster doses were given after 4-6 months based on interim serology results using a multiplex bead-based assay (MIA). Final analyses were based on serum bactericidal antibody titers (rSBA).

RESULTS

A total of 12 subjects were enrolled (average 25 years old, range 19-48). MenACWY-CRM₁₉₇ became unavailable during the course of the study and was only evaluated for a 1/10th dose. This dose resulted in less than complete seroprotection for serogroup A but complete protection against the other serogroups. MenACWY-TT was evaluated for a 1/10th and 1/5th dose level. Both fractional doses of MenACWY-TT resulted in complete seroprotection against all vaccine serogroups. Geometric mean titers 1 month after vaccination were lower and decayed faster in the MenACWY-CRM₁₉₇ group. Adverse events were mild and there were no serious adverse events.

CONCLUSION

Fractional intradermal vaccination against meningococcal disease with quadrivalent conjugate vaccine appears to be safe and effective in our small dose finding study. Tetanus toxoid conjugated vaccine (Nimenrix®) shows a trend towards higher antibody levels compared to CRM₁₉₇-conjugated vaccine (Menveo®). The 1/5th fractional dose of MenACWY-TT appears to result in higher antibody levels than does the 1/10th dose. These results can be used for a larger non-inferiority study. This trial was registered in clinicaltrials.gov under NCT01782066.