It is thought that this contributes to the violent cough and also the likelihood that pneumonia can follow. The pertussis component until very recently was killed whole cells and was highly reactive, even leading to permanent neurological damage in a small number of children. Because of this many countries made pertussis vaccination optional, but it remained mandatory in the United States, largely because it was thought that the disease was far worse than any of the side effects. New vaccines have now been developed, and, in fact, vaccines composed of only the FHA and inactivated toxin have been in use in some countries for some time. Although this country lagged somewhat in their approval of these, they have recently been recommended for use in the US for all ages of children.
Early reports indicate that the new vaccines have a very low rate of adverse reactions.
The old vaccine should now never be used.