Impact of a vaccination campaign on adult immunity to diphtheria

Objectives: to raise the level of immunity to diphtheria in the adult popul ation of Stockholm by a vaccination campaign. The : rationale behind the ca mpaign, conducted during 1995-1996, was the re-emergence of epidemic diphth eria in the countries of the former Soviet Union and earlier surveys of imm unity 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 d oses given and any side-effects. The effect on immunity was evaluated in 19 98-1999 by measuring the neutralising antibodies in blood samples from 1863 inhabitants, chosen by random stratified sampling. Vaccines and vaccinatio ns: three doses of diphtheria (D) or diphtheria-tetanus (DT) vaccine were g iven to those without documented previous vaccination; others received a bo oster dose. The DT vaccine, with the D component purified before toxoiding, contained 15 Lf of D and 7.5 Lf of T per mi, and was given in 0.5 mi doses for the two priming doses and 0.25 mi as booster. Results: 184 969 doses o f D or DT vaccine were given to 99 939 individuals. Of the vaccinees, 65% w ere 50 years of age or older and 60% were women. The highest rates of repor ted 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 con centrations in the age cohorts targeted, and especially in women, less well protected than men. Conclusions: a vaccination campaign, targeting the adu lt part of a population, can result in a major improvement in immunity to d iphtheria with only a few and minor side-effects with a DT vaccine where th e D component was purified prior to toxoiding. Extending national immunisat ion programmes to include adults would, however, seem preferable. (C) 2000 Elsevier Science Ltd. All rights reserved.