The persistence of tuberculin sensitivity following oral BCG vaccination in the Netherlands

Abstract

Certain anomalies in the tuberculin test results in Netherlands schoolchildren in the late 1960s and in recruits a few years later are shown to have arisen from the persistence of tuberculin sensitivity in some of the 10 000 newborn children who were given oral BCG vaccine in the early 1950s. More than 90 % of these oral BCG vaccinations were given in 1950 or 1951 in Amsterdam, Delft or Hilversum, but because of the absence of a scar or any record, individuals who were vaccinated cannot now be distinguished from the much larger numbers of unvaccinated subjects. The cohorts of Dutch children born in 1950 and 1951 showed excess positivity, compared with earlier and later cohorts, when tuberculin tested at different ages in adolescence and as army recruits, and this was especially noticeable among current residents in these three cities. It is estimated that less than 10 % of those given oral BCG vaccine in the Netherlands in 1950 or 1951 showed positive reactions at ages 12 and 13, but about 20 % did at age 16, and about 45 % at age 18. A review of data on tuberculin sensitivity several years after intradermal BCG vaccination in the newborn or in young children suggests that sensitivity persists in only a relatively small proportion for a long period (in perhaps about 45 % after 7 years and less after a longer period), unless boosted by intervening tuberculin tests. The present data on oral BCG vaccination in the newborn conform to the same pattern. Few of those tested at ages 12 and 13 had earlier tuberculin tests, whereas many of those tested at older ages will have had earlier tests in the national scheme then operating for annual testing from age 12 to 18 years.