Immunogenicity of Simulated PCECV Postexposure Booster Doses 1, 3, and 5 Years after 2-Dose and 3-Dose Primary Rabies Vaccination in Schoolchildren

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.

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.

Tollwutprophylaxe: So beraten Sie in der Hausarztpraxis

Auch wenn von Reisen während der COVID-19-Pandemie gegenwärtig noch weitgehend abzusehen ist, bleibt Tollwut ein wichtiges Thema, dem Sie sich spätestens dann wieder widmen müssen, wenn die ersten Kurzentschlossenen zur Reiseberatung in Ihrer Praxis erscheinen werden. Dieser Beitrag frischt Ihr vorhandenes Wissen auf und informiert Sie insbesondere über das von der WHO propagierte verkürzte präexpositionelle Impfschema.

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.

Rabies Antibody Response After Booster Immunization: A Systematic Review and Meta-analysis

Although fatal once symptomatic, rabies is preventable by administration of pre- and post-exposure vaccines. International guidelines suggest lifelong protection by a pre-exposure vaccination scheme followed by timely post-exposure vaccines. Rapidity and magnitude of the antibody recall response after booster inoculation are essential, as many people have been previously immunized a long time ago. The objective of this study was therefore to systematically review the evidence on the boostability of rabies immunization to date. We included 36 studies, of which 19 studies were suitable for meta-analysis. Reduced antibody levels were found after intradermal primary schedules as compared to intramuscular schedules. However, responses after booster immunization were adequate for both routes. Although studies showed that antibody levels decline over time, adequate booster responses were still retained over long time intervals indicating that post-exposure treatment is effective without extra measures after long periods of time.

Evaluating new rabies post-exposure prophylaxis (PEP) regimens or vaccines

The development of human rabies vaccines has evolved dramatically from the first crude nerve tissue vaccine produced then administered in the presence of Louis Pasteur in 1885. New cell culture technology has enabled highly potent and well-tolerated rabies vaccines to be produced that have reduced the volume and number of doses required to save human lives after exposure. However, these highly potent vaccines are still unaffordable to many patients living at risk of exposure on a daily basis. The cost of post-exposure prophylaxis (PEP) is not only related to the direct cost of rabies biologicals and equipment but is also associated with indirect costs that patients incur as a result of travel, loss of work time (income loss), and accommodation over the period of time that a PEP regimen requires to be completed. This paper summarizes the particular criteria that the SAGE Working Group and WHO personnel reviewed as part of the evaluation process for recommending the new one-week intradermal vaccination regimen (2-2-2-0-0) for rabies post-exposure prophylaxis. These criteria included: Cost-effectiveness; evaluation of number of doses; seroconversion after vaccination; efficacy; safety; and patient follow-up.

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.

Intradermal vaccination for infants and children

Intradermal (ID) vaccination induces a more potent immune response and requires lower vaccine doses as compared with standard vaccination routes. To deliver ID vaccines effectively and consistently, an ID delivery device has been developed and is commercially available for adults. The clinical application of ID vaccines for infants and children is much anticipated because children receive several vaccines, on multiple occasions, during infancy and childhood. However, experience with ID vaccines is limited and present evidence is sparse and inconsistent. ID delivery devices are not currently available for infants and children, but recent studies have examined skin thickness in this population and reported that it did not differ in proportion to body size in infants, children, and adults. These results are helpful in developing new ID devices and for preparing new vaccines in infants and children.

Rabies pre-exposure vaccination of children with purified chick embryo cell vaccine (PCECV)

Human rabies, mainly transmitted by dog bites, remains a major public health problem in developing countries. In Asian countries, such as India or the Philippines, where large free-ranging dog populations exist, the human death toll stays high. Children under the age of 15 y are at particular risk, representing up to half of the dog bite victims. While pre-exposure prophylaxis (PrEP) is commonly used in travelers from developed countries visiting areas of high endemicity, rabies vaccination is rarely used in highly endemic countries in contrast to post-exposure prophylaxis (PEP). Purified Chick Embryo Cell Vaccine (PCECV, Rabipur®/RabAvert®, Novartis Vaccines and Diagnostics) is approved for pre- and post-exposure prophylaxis, either by the intramuscular route, or--where registered--by the intradermal route of administration. In more than 25 y of use, PCECV has been widely used for PrEP in children. This review summarizes the pediatric pre-exposure clinical trials using PCECV. In total, PCECV has been administered to more than 1,200 children in clinical trials, from toddlers to those in elementary school, using intramuscular and intradermal schedules, demonstrating safety and immunogenicity. PrEP as part of routine pediatric vaccination programs may have a major role to play in human rabies prevention. Extensive clinical experience with PCECV supports intramuscular and intradermal PrEP in children as one pillar of human rabies prevention in developing countries.