Table 3.

Estimated protection from reinfection over time from published studies

Author, year	Measure of initial infection	Severity of reinfection	Estimated protection by time (%, 95% CI)
Hansen (2021) [44]	Any PCR positive	Any PCR positivea	3–6 months: 79.3 (74.4–83.3)  ≥ 7 months: 77.7 (70.9–82.9)
Nordstrom (2022) [45]	Any documented infection	Any document infectionb	3–6 months: 96.0 (95.0–96.0)  ≥ 9 months: 93.0 (92.0–94.0)
		Hospitalisationb	3–6 months: 89 (86.0–91.0)  ≥ 9 months: 78 (66.0–85.0)
Spicer (2022) [46]	Any PCR positive	Any PCR positivea	91–120 days: 70.1 (65.6–74.0) 241–270 days: 79.8 (65.0–88.4)
Sheehan (2021) [47]	Any PCR positive	Any PCR positivea	90–150 days: 60.0  ≥ 210 days: 93.9
	Any PCR positive	Symptomatic PCR positivea	90–150 days: 71.0  ≥ 210 days: 91.5
Hall (2022) [28]	Any PCR positive	Any PCR positivec	≤ 1 year: 86.0 (0.81 to 0.89)  > 1 year: 69.0 (0.38 to 0.84)

^aStudy performed prior to widespread VOC

^bStudy performed during three waves of SARS-CoV-2: prior to widespread sequencing, prior to alpha variant becoming dominant, and after the alpha variant became dominant

^cThe initial infections occurred prior to widespread VOC, while the follow-up occurred during a period when the delta variant was predominant