Yeah, from what I've heard the T-cell epitopes are conserved between the the variant that was first detected in Wuhan (the one the vaccines are based on), and the "Delta" variant (the one that was apparently first detected in India), so it should at least make the disease less severe, even if it can't block infection if you don't have the best immune system, for example in older people. The transmission should be reduced about 50% in very close contacts if you get infected, and close to 100% if you don't, unless there's some sort of near-impossible T-cell evasion. The data on transmission is pretty sketchy though, not controlled.
From what I understand (I'm no microbiologist but I'll take a look at Pamela Anderson's no-no square for science), the T-cell epitope in SARS-CoV-2 is the spike protein and not the membrane protein - The latter is definitely well-conserved, with the former already showing heterogeneity by last September:
Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to an outbreak of a pandemic worldwide. For better understanding the viral spike (S) protein variations and its potential effects on the interaction with the host immune system...
www.frontiersin.org
The majority of the troublesome mutations so far (such as enhanced ACE2 receptor binding) involve the spike protein. We have actually been fortunate so far, as parallel domain mutations (ie. mutation to the membrane protein escalating interleukin production + spike protein heterologue expression + enhanced shuttling with GRP=78 hasn't happened (yet? hope not).
This is the underlying reason as to why the first wave of vaccines are due to become progressively less effective as time passes and the longer SARS-CoV-2 is in circulation, as the sum number of mutations would obviously increase (irrespective of mutation rate) and the chance of escape mutations (especially after selection pressures are applied, such as with languid vaccine rollout) occurs.
Given the most immediate site of mutation so far is the spike protein, the immune response to said vaccines may offer partial protection at best against future variants with significant, evolutionarily advantageous changes to the spike protein.
Touching on your last sentence a bit, we received preliminary news from Israel that the Pfizer jab (which is arguably the current 'gold standard') is approx 30% less effective against the delta variant (offers only 65% protection, versus 95% against OG Wuhan). So, the prior expectations regarding poorer transmission blockage with subsequent strains have now been vindicated.
Returning to Styxhexenhammer briefly, and in relation to my second paragraph;
I distinctly recall Styx claiming, at the outset of the pandemic around March 2020, that he's '90% confident' that the virus 'would be harmless' after two or three waves, using the analogy of the Spanish Flu and Ebola.
That very clearly hasn't happened - The Brazil Manaus, British, Indian and India-Plus variants are all associated with worse morbidity and mortality compared to either of the OG Wuhan strains.
Additionally, India was already dealing with the British strain in late 2020-21 before the Indian strain surpassed it in both infectivity and mortality - This runs counter to the 'all viruses become less deadly' maxim that some, including Styx, were asserting.
I'm unsure if Styx has since conceded that his prognostication was based on superficial Darwinian principles and was made in a state of ignorance (fex. we had zero empirical data regarding
where in the RNA genome the virus would preferentially mutate in, and what its ramifications may be).
