Immunogenicity of a modified intradermal pre-exposure rabies vaccination schedule using a purified chick embryo cell vaccine: An observational study

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.

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.

Newcastle disease virus vectored rabies vaccine induces strong humoral and cell mediated immune responses in mice

Rabies is a devastating disease affecting almost all mammalian animal species including humans. Vaccines are available to combat the disease. Protection against the disease is rendered by assessing the humoral immune response. Recent reports suggest the role of cell mediated immune response (CMI) in assessing vaccine efficacy. In the present study, two live vectored vaccine candidates containing glycoprotein G of rabies virus were generated using the mesogenic Newcastle disease virus (NDV) strain R2B and another with NDV with an altered fusion protein cleavage site as backbones. The efficacy of these vaccine candidates on testing in experimental mouse model indicated generation of robust humoral and CMI responses. The recombinant NDV containing the altered fusion protein cleavage site with glycoprotein G showed the highest CMI response in mice indicating its usage as a potential live vectored vaccine candidate against the disease.

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.

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.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

A single center, open label study of intradermal administration of an inactivated purified chick embryo cell culture rabies virus vaccine in adults

In the USA, rabies vaccines (RVs) are licensed for intramuscular (IM) use only, although RVs are licensed for use by the intradermal (ID) route in many other countries. Recent limitations in supplies of RV in the USA reopened discussions on the more efficient use of available biologics, including utilization of more stringent risk assessments, and potential ID RV administration. A clinical trial was designed to compare the immunogenic and adverse effects of a purified chicken embryo cell (PCEC) RV administered ID or IM. Enrollment was designed in four arms, ID Pre-Exposure Prophylaxis (Pre-EP), IM Pre-EP, ID Booster, and IM Booster vaccination. Enrollment included 130 adult volunteers. The arms with IM administration received vaccine according to the current ACIP recommendations: Pre-EP, three 1mL (2.5 I.U.) RV doses, each on day 0, 7, and 21; or a routine Booster, one 1ml dose. The ID groups received the same schedule, but doses administered were in a volume of 0.1mL (0.25 I.U.). The rate of increase in rabies virus neutralizing antibody titers 14-21days after vaccination were similar in the ID and correspondent IM groups. The GMT values for ID vaccination were slightly lower than those for IM vaccination, for both naïve and booster groups, and these differences were statistically significant by t-test. Fourteen days after completing vaccination, all individuals developed RV neutralizing antibody titers over the minimum arbitrary value obtained with the rapid fluorescent focus inhibition test (RFFIT). Antibodies were over the set threshold until the end of the trial, 160days after completed vaccination. No serious adverse reactions were reported. Most frequent adverse reactions were erythema, induration and tenderness, localized at the site of injection. Multi use of 1mL rabies vaccine vials for ID doses of 0.1 was demonstrated to be both safe and inmunogenic.

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.