Threshold level of herd immunity of Peussis is -

Park&;s texbook of Preventive and Social Medicine 23rd edition Page no: 165 The control of peussis by immunization is still an unsolved problem Even if the level of immunization reaches 100 per cent, it is possible that the disease would not be entirely eliminated because whooping cough vaccines have never been claimed to be more than 90 per cent effective.