Non-specific Effects of BCG in Under-five Children

Plain-language summary

Studies have demonstrated that the reduction in mortality and morbidity due to vaccination extends beyond the targeted infections. This seems to result from the non specific effects of vaccines. BCG, a live attenuated vaccine against TB disease, administered to new borns, is one of the vaccines known to have non specific effects. In Portugal, between 1965 and June 2016, BCG was administered to all new borns. In July 2016, a clinical guideline established that only children under 6 years of age from high-risk groups should be vaccinated. In 2021, the first cohort of children not vaccinated for BCG reached 5 years of age and evidence is needed on the impact of this strategy. Aim: to investigate the incidence of specific and non-specific effects of BCG by comparing the incidence of TB disease and infection, mild and severe morbidity, and mortality in the first 5 years of life of children born between 2010 and 2021 according to their BCG status. Methods: historical birth cohort study of children born between 1st July 2010 and 30th June 2021. The investigators will create a single database that links data from the birth registry, the vaccination registry, the information systems of death certificates, epidemiological surveillance and TB surveillance, Diagnosis Related Groups and of primary health care of children born in the study period to reconstruct chronological sequences of morbidity and mortality events from birth until completion of 5 years of life or 30th June 2021. Only children born in Portugal, live-births and births coded as normal new-born will be included. New borns with low-birth weight (\<2kg), premature (\<37 weeks) and known or suspected HIV infections will not be included in the study. The follow-up period will be until completion of 5 years of age or 30th June 2022. Data will be analysed to compare the incidence of all-cause mortality (including TB), TB disease and severe and mild morbidity among BCG vaccinated and non-vaccinated children born during the reference period in a total of 11 birth cohorts and will comprise computation of person-time incidence rates for primary outcomes and the probability of surviving (Kaplan Meier method) first and fifth year of life or of not having a hospitalization, emergency department visit or a mild morbidity episode during the follow-up period according to exposure. To explore the effects of several variables on the survival outcomes we will use proportional hazards regression analysis.

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