Answer:
0.85 ( lowest value proportion to vaccinate )
Step-by-step explanation:
Using the herd immunity relationship
Vc = E - ( E / Ro )
Vc = critical vaccination level
E = vaccine effective against the transmission = 1
Ro = Basic reproduction number
lets assume the effectiveness of the transmission = 100% = 1
lets assume the
Vc = 1 - ( 1 / 3 ) = 67%
but the lowest value proportion to vaccinate = 85%