I’ve always thought that vaccinating elderly and first responders was less about stopping spread and more about reducing fatalities among the most vulnerable. After all it is the least vulnerable who are most likely to be the main spreaders, and until a reasonable portion of <65 year olds are vaccinated, the spread is likely to continue and probably even flatten before that point.

However since most countries in the world are in the middle of a 2nd/3rd wave, it makes absolute sense to vaccinate the vulnerable first rather than try race against the curve with a vaccination programme. Especially when the vaccination lag is longer than the spread.