Thank you for reading and responding. You’re right, mRNA vaccines are only trained on the spike protein. The passage you have highlighted is actually referring to convalescent immunity and immunity from vaccines that use whole viruses. My bad for not clarifying it and thank you for pointing that out. :D


With regards to mRNA vaccines, in general, the epitopes that bind to antibodies and the epitopes that bind to T-cells are different. And the paper that I’ve described found that 80%-88% of the T-cell specific epitopes in the spike protein were fully conserved between the wild-type and the Omicron variant. Hence, even if the T-cells are trained on just the spike protein, they will still confer some degree of immunity. Hopefully this helps solve the confusion.