Collaborative study on influenza vaccine clinical trial serology - part 2: reproducibility study.

A collaborative study was run by the Biological Standardisation Programme (BSP) under the aegis of the European Directorate for the Quality of Medicines & HealthCare (EDQM, Council of Europe) and the European Union (EU) Commission, to address the issue of the poor standardisation of serological assays used for the evaluation of seasonal influenza vaccines in Europe. The Phase 1 of the study focused on the compliance to Committee for Human Medicinal Products (CHMP) criteria by 6 manufacturers and 5 public laboratories. It confirmed the poor inter-laboratory correlation of haemagglutination inhibition (HI) test results. Phase 2 consisted in a reproducibility study examining the impact of extended method standardisation and the use of reference sera on inter-laboratory variation. Six manufacturers and 5 public laboratories contributed HI results, while the 5 public laboratories also performed single radial haemolysis (SRH) tests on the same sample panels. Results showed that method standardisation failed to significantly improve the inter-laboratory variation. Correction for pre-vaccination titres (Beyer correction) was found to have limited effect to improve the bias constituted by the Protection Rate (PR) criterion. The reasons underlying the difficulty in standardisation of HI and SRH tests are discussed and improved approaches for the compliance testing to CHMP criteria are suggested.