Intervention implementation
Details of Germ Defence were emailed to 2870 intervention arm GP practices. The practice unique Germ Defence weblink was accessed by 1094 intervention arm practices (38.1%) at least once. Patient engagement within intervention arm practices ranged from no engagement (when no patient in a practice visited the Germ Defence website) to engagement from 48% of patients registered with the practice. There was no association between practice list size and proportion of uptake (Practice engagementUsage levels: none 0 user, low 0.01 to 0.99% of list, medium 1.00 to 10.99% of users, high 11 to 100% of usersFurther analysis explored whether usage rates [percentage of practice patient list that used the intervention: low (0–0.99%), medium (1–10.99), high (11 +)] differed across varying practice characteristics including population levels of deprivation (IMD), income, employment, education and skills, health and disability, barriers to housing and services, living environment, age, proportion of minority ethnic group and practice quality and outcomes framework performance. Engagement did not differ across any metrics except for ethnicity proportion, in which practices with high levels of uptake (> 11%) had a lower proportion of minority ethnic groups (10.5%) compared to practices with lower levels of use (low: 15.1%, medium: 15.8%). We report analysis of all characteristics in detail in Supplementary file 