«Recommendations to Assure the Quality, Safety and Efficacy of Live Attenuated Yellow Fever Vaccines Proposed replacement of: TRS 872, Annex 2 and ...»
Recommendations to Assure the Quality, Safety and Efficacy of Live
Attenuated Yellow Fever Vaccines
Proposed replacement of: TRS 872, Annex 2 and Amendment to TRS 872,
Annex 2, TRS (in press) (ECBS 2008)
© World Health Organization 2010
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Adopted by the 61st meeting of the WHO Expert Committee on Biological Standardization, 18 to 22 October 2010. A definitive version of this document, which will differ from this version in editorial but not scientific details, will be published in the WHO Technical Report Series.
Page 2 Recommendations published by the WHO are intended to be scientific and advisory. Each of the following sections constitutes guidance for national regulatory authorities (NRAs) and for manufacturers of biological products. If a NRA so desires, these Recommendations may be adopted as definitive national requirements, or modifications may be justified and made by the NRA. It is recommended that modifications to these Recommendations be made only on condition that modifications ensure that the vaccine is at least as safe and efficacious as that prepared in accordance with the recommendations set out below. The parts of each section printed in small type are comments for additional guidance intended for manufacturers and NRAs, which may benefit from those details.
Table of contents Introduction
Part A. Manufacturing recommendations............
A.2 Certification of the substrain of 17D virus for use in vaccine production
A.3 General manufacturing recommendations
A.4 Control of source materials...
Control of vaccine production
A.5 Filling and containers
A.6 Control tests on final lot
A.7 A.8 Records
A.9 A.10 Labelling
A.11 Distribution and shipping
A.12 Stability, storage and expiry date
Part B. Nonclinical evaluation of live attenuated yellow fever vaccines
B.1 Characterization of a new candidate yellow fever vaccine................
B.2 Immunogenicity and other pharmacodynamic studies
B.3 Toxicity assessment
Part C. Clinical evaluation of live attenuated yellow fever vaccines Error! Bookmark not defined.
C.1 General considerations
C.2 Safety and immunogenicity studies
C.3 Post-marketing studies and surveillance
Part D. Recommendations for national regulatory authorities
D.2 Release and certification Authors and Acknowledgements
Appendix 1 Genealogy of 17D yellow fever vaccine strains
Appendix 2 Page 3 Tests in non-human primates of new virus master and working seeds
Appendix 3 Example, for guidance, of a summary protocol for the testing of new master and working seeds in the monkey safety test as described in Appendix 2
Appendix 4 Example, for guidance, of cell-culture techniques for the potency evaluation of yellow fever vaccine
Appendix 5 Model summary protocol for manufacturing and control of live attenuated yellow fever vaccines
Appendix 6 Model certificate for the release of live attenuated yellow fever vaccine by national regulatory authorities
Introduction Requirements for yellow fever vaccine (Requirements for Biological Substances No. 3) were first formulated by a WHO Study Group in 1958 (1). The Requirements embodied recommendations made by the first WHO Expert Committee on Yellow Fever Vaccine (2), and they applied to vaccine prepared from a suitable strain of yellow fever virus. The vaccine was intended to be given by subcutaneous injection. Conformity with these Requirements has been the basis for WHO approval of yellow fever vaccine used for vaccination and revaccination against yellow fever in connection with certification for the purposes of international travel (3), and such approval has been given only to vaccine prepared using seed derived from the 17D strain of yellow fever virus. Yellow fever continues to be the only disease for which a certificate of vaccination is required for entry into some countries and the update of the International Health Regulations (4) increased attention to the need for such certificates. The Requirements have been used also by national regulatory authorities (NRAs) for the control and approval of yellow fever vaccine used in national immunization programmes.
In 1969, the twenty-second meeting of the WHO Expert Committee on Biological Standardization (ECBS) agreed that developments in virology in general and in the manufacture and control of yellow fever vaccine in particular warranted a revision of the existing Requirements, with due consideration of both their national and international application (5). In 1975 the twenty-seventh meeting of the ECBS formulated revised Requirements for yellow fever vaccine (6). Much experience was gained with the preparation of yellow fever vaccine since 1975, and a further revision of the Requirements was approved by ECBS in 1995 (7).
A collaborative study to assess the suitability of a candidate International Standard (IS) for yellow fever vaccine indicated that the use of a standard for measuring potency which has been assigned an arbitrary unitage in International Units (IU) would markedly improve the agreement in the results between laboratories (8, 9). The first IS for yellow fever vaccine with an assigned potency of 104.5 IU per ampoule was established in 2003 (10). A proposal to amend the requirements for yellow fever vaccine so that the potency of such vaccines be Page 4 expressed in IU per dose and that the dose recommended for use in humans shall not be less than 3.0 log10 IU, with no upper limit on the quantity of virus in a dose was approved by ECBS in 2008 (11,12). The availability of an IS for yellow fever vaccine with an assigned potency in IU so that assay in mice and expression of virus titres in LD50 is not required, also impacts on other sections of the requirements established in 1995 (11).
In 2008, ECBS recommended that the requirements for yellow fever vaccines be reviewed as it is over 10 years since they were published and sections on nonclinical and clinical evaluation for new candidate yellow fever vaccines are also required. To facilitate this process, WHO convened a meeting of experts, regulatory professionals and other stakeholders in Geneva, in May 2009 to discuss the scientific basis for the present revision of the requirements and to develop revised recommendations for yellow fever vaccines (13).
The scope of the present Recommendations encompasses live attenuated yellow fever vaccines derived from strain 17D, including 17D-204 and 17DD substrains.
This document should be read in conjunction with the relevant WHO guidelines including those on nonclinical (14) and clinical evaluation (15) of vaccines.
General considerations The yellow fever virus is small (50 nm) and consists of a nucleocapsid with core protein (13kDa) containing single-stranded, positive-sense RNA surrounded by a lipoprotein envelope (16). The lipoprotein envelope contains two proteins, a small membrane protein (8kDa) and an envelope glycoprotein (53kDa), which is the major target of neutralizing antibodies and has type- and group-specific antigenic determinants. Wild-type yellow fever viruses have genomes of similar length but vary depending on the size of the 3’ non-coding region (17,18). Based on sequence analysis, wild-type yellow fever virus strains have been classified into at least seven genotypes: five in Africa and two in South America. The genotypic variation is not accompanied by significant antigenic differences across strains and there is a single serotype (19).
The genome of the yellow fever virus strain from which all 17D vaccines are derived has been completely sequenced and has been found to contain 10,862 nucleotides, which encode three structural and seven non-structural proteins (20). There are two substrains in use today for the manufacture of 17D vaccine, namely 17D-204 and 17DD. 17D-213 is a derivative of 17D-204 that has gained a glycosylation site in the E protein but differs significantly in phenotype from 17D-204. It is sometimes considered to be a substrain of 17D and sometimes referred to as 17D-213. Genomic sequencing has been reported for many of the yellow fever vaccine viruses and their seeds currently used by different manufacturers. These studies show that there are very few nucleotide and amino acid differences between the vaccine strains. The yellow fever vaccine strains that have been and are being used for vaccine manufacture and their history are summarized in Appendix 1.
Yellow fever is a viral haemorrhagic fever that is endemic in 32 countries in Africa and 13 countries in Central and South America (21).
Page 5 In 1900, a commission headed by the American physician Walter Reed confirmed that the disease was transmitted from human to human by the mosquito Aedes aegypti, a hypothesis proposed earlier by the Cuban physician Carlos Finlay in 1881 (22). There are two epidemiological patterns of yellow fever virus transmission: the urban cycle and the forest cycle (also known as the jungle or sylvan cycle). The two patterns of transmission lead to a clinically identical disease. In the Americas, the yellow fever virus circulates by means of an endemic, forest cycle that results in up to several hundred reports of infection primarily in non-immune forest workers per year, with occasional reports of isolated cases of urban yellow fever. In Africa, the virus circulates by means of both urban and forest cycles and periodically breaks out of its endemic pattern to infect large numbers of non-immune persons in the course of major epidemics (23).
The case-fatality rate of yellow fever can reach as high as 20% to 80% in severely ill patients who are hospitalized (24). Case-fatality rates are highest among young children and the elderly. There are no antiviral drugs for any flavivirus infection including yellow fever so the availability of vaccines is important for both resident populations and travellers.
When 17D vaccine was first used in the late 1930s/early 1940s, some problems were observed which were associated with under- or over-attenuation of the 17D strain on passage. These problems were resolved by the establishment of a virus seed lot system in
1945. As of 2009, more than 500 million doses of 17D vaccine had been administered (25) so there is a large amount of information available regarding vaccine safety. This vaccine has been shown to be very effective for the control of yellow fever during outbreaks and between epidemics. In 1990, the Global Advisory Group of the Expanded Programme on Immunization (EPI) recommended that all countries at risk of yellow fever should incorporate the vaccine in their routine immunization programmes. In Africa, 22 countries have introduced yellow fever vaccine in routine childhood immunization. Routine vaccination coverage in countries at risk in Africa has increased from 16% in 2000 (8 countries) to 43% in 2008. In the Americas, coverage rose from 64% to 91% (21). In this regard it is of note that the limited data on vaccination of individuals with immunosuppression associated with HIV infection suggest that seroconversion is reduced without an increase in adverse events following immunization (AEFI) (26).
Serious adverse reactions that have been reported associated with 17D yellow fever vaccine
administration and are of particular note include the following:
a. Hypersensitivity reactions, including anaphylaxis, are believed to be associated with egg protein due to the vaccine being grown in embryonated chicken eggs. However, gelatine used by some manufacturers may be implicated in some hypersensitivity reactions.
b. Yellow Fever Vaccine-Associated Neurologic Disease (YEL-AND) is a term recently introduced to define neurologic AEFIs that have occurred in temporal association with YF vaccination since 2000 (27). Encephalitis following 17D vaccination in vaccinees of any age was first described in the 1940s (28). The incidence rate was dramatically reduced to background levels after introduction of the seed lot system for manufacture of 17D Page 6 vaccines. However, in the 1950s, there were several individual case reports describing a self-limited encephalitis in infants and very young children that occurred in temporal association with 17D vaccines manufactured in accordance with the seed lot system (see section A.4.2.1). With one exception, these children recovered fully with no sequelae.
However, these reports led to the recommendation by WHO that infants 6 months of age and below should not be vaccinated (19). Adoption of this recommendation and unknown factors led to the virtual elimination of post-vaccinal encephalitis by the mid-1960s.