Scar formation and tuberculin conversion following BCG vaccination in infants: A prospective cohort study

There is considerable variation in BCG scar failure rate on available data and correlation between BCG scar and tuberculin conversion remains controversial. Through this study we aimed to determine the scar failure rate and tuberculin conversion in term infants vaccinated with BCG within the first month. A prospective cohort study was conducted among 85 consecutive infants weighing >2 kg attending the immunization clinic of a medical college hospital. Fifteen subjects who could not complete the follow up were excluded. Total of 70 cases were analyzed. All babies were administered 0.1 ml of BCG and examined at 3 months (+1 week) for scar. Tuberculin test was done with 5TU PPD. An induration of >5 mm was considered positive. Statistical analysis was done using Microsoft Excel and SPSS-22. Out of the 70 infants, 41 (58.6%) were males. Although majority (72.9%) of infants were vaccinated within 7 days, only 18 (25.7%) received BCG within 48 hours of birth. Sixty-four (91.4%) had a visible scar at 12 weeks post vaccination representing a scar failure rate of 8.6%. Tuberculin test was positive in 50 (71.4%). The mean ± s.d. for scar and tuberculin skin test (TST) reaction size was 4.93 ± 2.01 mm and 6.01 ± 3.22 mm, respectively. The association between scar formation and tuberculin positivity was highly significant (P < 0.001). There was significant correlation between scar size and TST size (r = 0.401, P = 0.001). Less than 10% of infants fail to develop a scar following BCG vaccination. There is good correlation between scar positivity and tuberculin conversion.