Table 3.

Comparison of infection and reinfection rates and estimated protection against reinfection with severe acute respiratory syndrome coronavirus 2 in healthcare workers

Period	Population	Confirmed new infection during follow-up	Person days of follow-up	Rate ratio (95% CI)	Estimated protection (95% CI)
Exposed	5,349	97	20,562	0.052 (0.043-0.064)	94.8% (93.6-95.7)
Unexposed	12,806a	4406	2,006,677b	1 (ref)	-

The comparison is made based on days of exposure and during follow-ups based on Poisson regression analysis. Exposed periods are periods of follow-up time contributed by individuals with previous infection; unexposed periods are contributed by individuals without a previous infection;

^a: 4,406 were infected during the study and 8,400 uninfected;

^b: 41,571 related to the infected group and 1,965,106 related to the uninfected group.