Generic downscaling of containment requirements for work with viral replicons derived from alphaviruses and flaviviruses

Advisory reports | 23.12.2022 | CGM/221223-01

Much research is being done on the development and application of ‘viral replicons’. Viral replicons are derived from viruses (virus vectors) and are used, among other things, in research on vaccines and cancer. After infecting a cell, replicons are still able to replicate their viral genome, but are not able to form new virus particles and are therefore unable to spread further. This is because one or more genes encoding for proteins that make up the virus particle (the structural proteins) are deleted or replaced by a transgene (the gene of interest).

The structural proteins can be externally added during production of the replicons, resulting in the generation of packaged replicons, the viral replicon particles. These replicon particles can infect a cell once, but thereafter are incapable of forming new virus particles because the structural genes are not present in the genome. Examples of replicons are the self-amplifying mRNA vaccines against COVID-19 and influenza currently under development.

In view of the increase in the number of requests for advice on assigning containment levels for work with replicons, COGEM commissioned a research project on various aspects of replicon systems. Based in part on the research results and with the aim of streamlining the authorisation procedures, COGEM has drawn up generic advice on containment levels for work with viral replicons. This generic environmental risk assessment is limited to replicons derived from alphaviruses (genus Alphavirus) and flaviviruses (genus Flavivirus).

COGEM is of the opinion that given the characteristics of these replicons and replicon particles, generic downscaling of containment requirements is possible. Depending on which genes have been deleted, COGEM advises the following:

  • Laboratory work with ‘naked’ alphavirus or flavivirus replicons can be carried out at containment level I, or at one level lower than the pathogenicity class of the parental virus.
  • Laboratory work with replicon particles can be carried out at one level lower than the pathogenicity class of the parental virus.
  • Generic conditions apply to work with both naked replicons and replicon particles: the cells used must contain no related alphaviruses or flaviviruses, and the transgenes used must not restore the removed functions.
  • In addition, replicon particle preparations must not contain any virus generated during production that is capable of replicating and spreading.

When the above conditions are met, COGEM considers that the environmental risks of carrying out work with alphavirus and flavivirus replicons at the stated containment levels are negligible.


The COGEM advise can be found under the button ‘download publication’. The COGEM research report can be found on a different page. Go to the research report.

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