Pfizer says its vaccine is preventing 91% of coronavirus cases in the six months after people are immunised.
And a separate study shows even people in their 80s and 90s are producing impressive levels of antibodies after receiving both doses of the vaccine.
Only 63% of them, however, also produce the T-cells that help maintain those antibodies in the longer term.
So 90% of populations need to be vaccinated needed I guess, to reach the 70-85% herd immunity if T-cell protection wading in and out