(a) Neither a public entity nor a public employee is liable for an injury resulting from the decision to perform or not to perform any act to promote the public health of the community by preventing disease or controlling the communication of disease within the community if the decision whether the act was or was not to be performed was the result of the exercise of discretion vested in the public entity or the public employee, whether or not such discretion be abused.
(b) Neither a public entity nor a public employee is liable for an injury caused by an act or omission in carrying out with due care a decision described in subdivision (a).