Longish quote about Marek's Diseases in chickens in next few Tweets, and then I wanted to ask those who…

Longish quote about Marek's Diseases in chickens in next few Tweets, and then I wanted to ask those who understand vaccines if the Covid vaccines are 'leaky' in this same way, with the same possible consequences? (Thanks to @iko_iko11 and Wikipedia). /1 #COVID19Aus

"Under normal conditions, highly virulent strains of the virus are not selected for by evolution. This is because such a severe strain would kill the host before the virus would have an opportunity to transmit to other potential hosts and replicate. Thus, less virulent..."/2

"...strains are selected. These strains are virulent enough to induce symptoms but not enough to kill the host, allowing further transmission. However, the leaky vaccine changes this evolutionary pressure and permits the evolution of highly virulent strains." /3

"The vaccine's inability to prevent infection and transmission allows the spread of highly virulent strains among vaccinated chickens. The fitness of the more virulent strains is increased by the vaccine." /4

"The evolution of Marek's disease due to vaccination has had a profound effect on the poultry industry...Highly virulent strains have been selected to the point that any chicken that is unvaccinated will die if infected." /end

@MackayIM is there anything here that's analogous with our Covid situation?