Yeast is a eukaryote, cheap, can be easily cultivated, has well-established fermentation processes and large-scale production capabilities. Availability of complete genome sequence, well-established genetic, inherent natural adjuvant and non-pathogenic nature of yeast species like Saccharomyces cerevisiae make it an ideal model system for the development of vaccines. Stay safe! All the best!

Thank you so much Siya, very much appreciated. Stay safe and well and with all best wishes. Tracey

"Yeast" is not a distinct taxonomic group. Although the term is casually used to describe fungi that grow in the morphology under lab culture conditions, it's generally been found that any fungus can grow in the yeastlike morphology.

There are two possible approaches for this interesting question : one is related to viruses of yeasts (see the proposed elements hereafter) ; the other is non-yeast viruses that could be present in a process involving yeast, for example in a fermentation to produce medical molecules like vaccines. In the later case, the inocuity, the safety of the fermentative product impose to ensure that these non-yeast viruses are unable to survive. Some studies have evaluated this risk, see for example :

Article Viricidal Effects of Lactobacillus and Yeast Fermentation

Following is an extract (an excellent summary) from the article : Yeast for virus research, by RY Zhao in

Microb Cell. 2017 Oct 2; 4(10): 311–330. Published online 2017 Sep 18. doi: 10.15698/mic2017.10.592

link

Article Yeast for virus research

There are also many benefits of using yeasts as model systems to study viruses of higher eukaryotes such as plant, animal or human viruses. The main reason is because yeasts carry their own indigenous viruses. Both positive sense (+) double stranded RNA (dsRNA) viruses, (+) single stranded RNA (ssRNA) viruses and retrotransposon elements have been reported in yeasts and other fungi 12,13. For example, studies of yeast killer viruses have helped us to study cellular necrosis and apoptosis during virus-host interaction 14,15,16,17, and to understand potential cellular viral restriction factors toward viral infections 18,19. Since the integration process of yeast retrotransposons resembles in many ways retroviral integration, molecular studies of fission yeast Tf elements or budding yeast Ty elements provided insights into functions of retroviruses such as HIV or murine leukemia viruses 20,21,22.

I selected some of the above references which are more related to your question :

Yeast virology

https://www.fasebj.org/doi/abs/10.1096/fasebj.3.11.2550303

Viruses in fungi: infection of yeast with the K1 and K2 killer viruses

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC305071/

The viral killer system in yeast: from molecular biology to application

https://academic.oup.com/femsre/article/26/3/257/497293

Caspase-dependent and caspase-independent cell death pathways in yeast

https://scholar.google.com/scholar_lookup?journal=Biochem+Biophys+Res+Commun&title=Caspase-dependent+and+caspase-independent+cell+death+pathways+in+yeast.&author=F+Madeo&author=D+Carmona-Gutierrez&author=J+Ring&author=S+Buttner&author=T+Eisenberg&volume=382&issue=2&publication_year=2009&pages=227-231&pmid=19250922&doi=10.1016/j.bbrc.2009.02.117&

Thank you so much Herve for your very detailed reply, I truly appreciate you taking the time to guide me and for providing such a detailed and informative response. I'm extremely grateful to you. Stay safe and well and with all my best wishes, Tracey.