"Figure 3: Seroconversion rate for staff by school type; Round 1 to 2, and Round 2 to 4","" "England, 3 to 20 November 2020 (Round 1), 30 November to 11 December 2020 (Round 2), and 15 to 31 March 2021 (Round 4)","" "","" "Notes","1. Data are unweighted. 2. The average follow-up time between Rounds 1 and 2 was 3 weeks and between Rounds 2 and 4 it was 15 weeks, for comparability a seroconversion rate has been calculated and expressed per 1,000 person-weeks. More details can be found in the [methodology](https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/methodologies/covid19schoolsinfectionsurveymethodsandfurtherinformation). 3. These seroconversion figures do not control for other factors that may affect the probability of seroconverting; for example different distributions between local authorities of those sampled and different age distributions. 4. Staff includes all employees working in the school for example, teachers, teaching assistants, support staff. 5. All results are provisional and subject to revision." "Unit","Per 1,000 person-weeks" "","" "School Type","Rate (per 1,000 person-week)","Lower 95% confidence interval","Upper 95% confidence interval" "Primary School Rounds 1 to 2","4.5","2.0","8.4" "Primary School Rounds 2 to 4","7.8","6.0","9.9" "","","","" "Secondary School Rounds 1 to 2","5.4","3.6","7.8" "Secondary School Rounds 2 to 4","5.0","4.0","6.1"