Impact of a vaccination campaign on adult immunity to diphtheria

Abstract

Objectives: to raise the level of immunity to diphtheria in the adult population of Stockholm by a vaccination campaign. The rationale behind the campaign, conducted during 1995–1996, was the re-emergence of epidemic diphtheria in the countries of the former Soviet Union and earlier surveys of immunity to diphtheria showing low levels of protection in adults. Design and main outcome measures: the impact of the vaccination campaign was measured by recording the age and sex of vaccinees, the type and number of vaccine doses given and any side-effects. The effect on immunity was evaluated in 1998–1999 by measuring the neutralising antibodies in blood samples from 1863 inhabitants, chosen by random stratified sampling. Vaccines and vaccinations: three doses of diphtheria (D) or diphtheria-tetanus (DT) vaccine were given to those without documented previous vaccination; others received a booster dose. The DT vaccine, with the D component purified before toxoiding, contained 15 Lf of D and 7.5 Lf of T per ml, and was given in 0.5 ml doses for the two priming doses and 0.25 ml as booster. Results: 184 969 doses of D or DT vaccine were given to 99 939 individuals. Of the vaccinees, 65% were 50 years of age or older and 60% were women. The highest rates of reported local reactions were 1.8–5.4% and of systemic reactions, such as fever, 0.2–0.8%. The campaign resulted in a significant increase in antitoxin concentrations in the age cohorts targeted, and especially in women, less well protected than men. Conclusions: a vaccination campaign, targeting the adult part of a population, can result in a major improvement in immunity to diphtheria with only a few and minor side-effects with a DT vaccine where the D component was purified prior to toxoiding. Extending national immunisation programmes to include adults would, however, seem preferable.