Hepatitis A immunoglobulin: an international collaborative study to establish the second international standard

Immunization against Hepatitis A

Worldwide, there are multiple formaldehyde-inactivated and at least two live attenuated hepatitis A vaccines now in clinical use. The impressive immunogenicity of inactivated vaccines is reflected in rapid seroconversion rates, enabling both preexposure and postexposure prophylaxis. Universal childhood vaccination programs targeting young children have led to significant drops in the incidence of hepatitis A both in toddlers and in susceptible nonimmune adults in regions with intermediate endemicity for hepatitis A. Although the safety of inactivated vaccines is well established, further studies are needed concerning the implications of fecal virus shedding by recipients of attenuated vaccines, as well as the long-term persistence of immune memory in children receiving novel immunization schedules consisting of single doses of inactivated vaccines.

The first international standard for antibodies to HPV 16

Current HPV vaccines and vaccine candidates are based on recombinant virus capsid proteins, so called virus-like particles (VLPs). Standardisation of assays for HPV capsid antibody will assist with epidemiology studies and future vaccine development. A World Health Organization international collaborative study was undertaken to assess the suitability of a freeze-dried serum, obtained from women naturally infected with HPV 16 and reactive against HPV 16 only, to serve as the International Standard for antibodies to HPV 16 in immunoassays and pseudovirion neutralisation assays. Eleven laboratories from nine countries participated in the collaborative study in which the candidate (NIBSC code 05/134) was assayed alongside samples from both vaccinees and naturally infected individuals. 05/134 had titres which were comparable to those obtained with serum from a naturally infected individual. Overall the variation between laboratories is similar to that observed in the previous study for samples from naturally infected individuals although slightly wider for sera from vaccinees. 05/134 has been established by the WHO Expert Committee on Biological Standardization as the 1st International Standard for antibodies to HPV 16, human serum, with an assigned potency of 5IUper ampoule.

Animal models and antibody assays for evaluating candidate SARS vaccines: summary of a technical meeting 25-26 August 2005, London, UK

Severe acute respiratory syndrome (SARS) emerged in the Guangdong province of China in late 2002 and spread to 29 countries. By the end of the outbreak in July 2003, the CDC and WHO reported 8437 cases with a 9.6% case fatality rate. The disease was caused by a previously unrecognized coronavirus, SARS-CoV. Drawing on experience with animal coronavirus vaccines, several vaccine candidates have been developed and evaluated in pre-clinical trials. Available data suggest that vaccines should be based on the the 180kDa viral spike protein, S, the only significant neutralization antigen capable of inducing protective immune responses in animals. In the absence of clinical cases of SARS, candidate vaccines should be evaluated for efficacy in animal models, and although it is uncertain whether the United States Food and Drug Administration's "animal rule" would apply to licensure of a SARS vaccine, it is important to develop standardized animal models and immunological assays in preparation for this eventuality. This report summarizes the recommendations from a WHO Technical Meeting on Animal Models and Antibody Assays for Evaluating Candidate SARS Vaccines held on 25-26 August 2005 in South Mimms, UK, provides guidance on the use of animal models, and outlines the steps to develop standard reagents and assays for immunological evaluation of candidate SARS vaccines.

Results of the first WHO international collaborative study on the standardization of the detection of antibodies to human papillomaviruses

Detection of genotype-specific human papillomavirus (HPV) capsid antibody in serum suggests past HPV infection. Also, these antibodies appear to correlate with vaccine-induced protection against infection, at least in animal models. However, each laboratory defines a reactive result differently and there is no agreed definition of what level of response indicates sero-reactivity. Standardization of assays for HPV capsid antibody will therefore assist with HPV vaccine development and epidemiology. This study was undertaken to investigate the specificity and sensitivity of assays in current use for measuring antibody to the major viral capsid protein L1 of HPV. Ten laboratories from 8 countries each analyzed 12 coded serum samples, which were derived from an uninfected woman, from naturally infected women and from individuals immunized with different vaccine candidates currently under clinical development. Study samples were assayed by methods in routine use in the participating laboratories. Nine assays were based on virus-like particles (VLPs) of 1 or more HPV genotypes. One laboratory used bacterially expressed major capsid protein L1 of HPV genotypes as antigen. There was considerable interlaboratory variation in estimated antibody levels. However, ranking of the potency of HPV 16 reactivity across the 12 test sera was consistent for all 10 laboratories. Expression of HPV 16 antibody levels relative to that of a single serum sample from an HPV16-infected woman considerably improved the interlaboratory assay comparability. Establishment of an International Standard for antibodies to HPV 16 would therefore facilitate the comparison of HPV antibody measurements between laboratories and assays.