Recommendations of drug regulatory agencies for mitigating adventitious agent in viral vaccines

Kimia Kardani,1 Elham mohit ,2,*

1. Department of Pharmaceutical Biotechnology, School of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran,
2. Department of Pharmaceutical Biotechnology, School of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran,



The safety and quality of the vaccines that are administered to a large populations of healthy people including children are paramount for public health. two critical components of safety are sterility and purity. adventitious agents that can be viruses, bacteria, mycoplasma, fungi, rickettsia, protozoa, parasites, and tse agents may accidentally introduced into a vaccine through starting materials used for production (cell substrates, porcine trypsin, bovine serum), or any other source materials from animal or human origin. as in-process inactivation steps compromise vaccine viability and immunogenicity agent, they are not part of the manufacturing process for live viral vaccines. however, for inactivated vaccines this steps are parts of the manufacturing process. several considerable contamination events e.g. sv40 contamination of polio vaccine, avian retrovirus and hepatitis b virus (hbv) contamination of yellow fever vaccine, endogenous avian retroviral particles in mmr vaccines and porcine circoviruses (pcvs) in rotavirus vaccine have been reported. these events highlighted that more vigilance is needed. according to the regulatory guidance documents, the risk of adventitious agent contamination should be assessed and mitigated through a tripod strategy. 1) the entry of contamination into production processes should be prevented by ensuring the quality of raw materials. 2) the contaminants should be detected by characterization of cell banks/virus seed stocks and by testing process intermediates. 3) the contaminants should be eliminated by incorporating virus inactivation/removal steps into the vaccine purification process which is challenging for whole live virus vaccines but practical for inactivated, subunit, and recombinant vaccines.


To prevent viral contamination, animal-derived components such as bovine serum and porcine trypsin should be screened for their viruses. according to regulatory guidelines the raw materials should be selected, qualified, and tested. furthermore, new technologies including temperature/short time (htst), c spectrum ultraviolet light (uv-c), gamma irradiation, and nano- or virus filtration are applied for cell culture or raw-material treatment to create barriers to viruses and mitigate bioreactor contamination risk.


Secondly, the viruses that may be present in the initial process, beginning with the cell bank and also in the process intermediates should be detected. the cell-bank should be tested for virus contamination. master cell banks (mcbs) should be tested for identity (phenotypic and genotypic, if recombinant) and purity. despite the differences among fda, the european medicines agency, and the world health organization guidelines, the absence of bacterial, fungal, and viral contamination should be demonstrated. a broad in vitro and in vivo assays are used for detection of extraneous viruses. in addition, antibody tests or polymerase chain reaction (pcr) panels are applied to detect species-specific viruses in cell lines. retrovirus particles can be detected using transmission electron microscopy (tem) and also pcr-based reverse transcriptase (pbrt) assays, also called product enhanced reverse transcriptase (pert) assays.


The final strategy to mitigate the risk of adventitious agent contamination in viral vaccines is to remove or inactivate viral contaminants downstream. the “viral clearance” or “viral removal” steps usually includes inactivation, chromatography, and/or virus filtration that removes any nonproduct virus. totally, these strategies can prevent the administration of adventitious virus-contaminated viral vaccines to patients.


Safety, viral vaccines, adventitious agent