Our trial was completed before children became eligible for COVID-19 vaccines, so pre-existing ChAd sensitisation was most likely due to cross-reactive natural exposures, rather than being vaccine-induced; however, we observed negative correlations between baseline ChAdOx1-GFP IFN-γ responses and day 63 and day 224 Ag85A-specific IFN-γ responses to ChAdOx1 85A–MVA85A (appendix 3 pp 9, 13), suggesting a possible adverse effect. The gene discussed is IFNG; the disease is COVID-19.