The geographic location (latitude) of studies evaluating protective effect of BCG vaccine and it's efficacy/effectiveness against tuberculosis

Abstract

Objective: To study association between the geographic location (latitude) of studies evaluating protective effect of BCG vaccine and it's efficacy / effectiveness against tuberculosis.

Methods: A comprehensive literature search was carried out to identify relevant studies. Data extraction from these studies included place of study (geographic latitude), study design and reported point estimate of protective effect of BCG vaccine against tuberculosis. Information on latitude was obtained from Oxford School Atlas for World Geography. A spearman rank correlation coefficient was estimated to study the association between the latitude of studies and protective effect of BCG vaccine.

Results: The Spearman's rank correlation coefficient was significant for all studies grouped together & trials and marginally non-significant for other observational studies. However it was not statistically significant for case-control studies and cohort studies. Overall rho (for 80 studies) between latitude and protective effect of BCG was calculated to be 0.3853 (p = 0.0004). The results thus demonstrated that, in general BCG appeared to provide greater protection at higher latitudes. Thus a correlation coefficient of 0.3853 between latitude and protective effect would indicate that (0.3853)(2) or 15% of the variance in protective effect was accounted for by latitude.

Conclusion: The study recognized an association between geographic locations of studies and reported protective effects of BCG vaccine against tuberculosis.