Absence of protective immunity against diphtheria in a large proportion of young adults.

The schedule of vaccination recommended worldwide for diphtheria, tetanus and other diseases, provides good immunity during childhood. However, little attention has been paid to effective immunity in adults. We have collected sera from 334 Italian Army recruits and tested them for the presence of protective immunity against diphtheria and tetanus. In vivo neutralization assays were performed on rabbits and mice and values below 1/100 IU ml-1 were considered negative. Of the recruits, 22.9% were negative for diphtheria, while only 5.3% had no protective immunity against tetanus. This finding shows that a large proportion of Italian young adults are susceptible to diphtheria, and this could be dangerous if they travel to sites where this disease is still endemic, or if they come into contact with people coming from such areas. A booster vaccination of young adults against diphtheria should become common practice to avoid this risk. To reduce the side effects which are often associated with diphtheria vaccination in adults, we have developed a vaccine which contains a highly purified, non-toxic mutant of diphtheria toxin. This vaccine is combined with tetanus toxoid and can be routinely used as a booster in adults.