Table 2. Comirnaty vaccine effectiveness in healthcare workers at various time intervals after COVID-19 vaccine administration, Treviso province, Italy, 27 December 2020–24 March 2021 (n = 6,423)^a .

Time of exposure	COVID-19 infections	PD	Incidence (per 1,000 PD)	Crude VE (%)	95% CI	Adjusted VEb (%)	95% CI
All casesc
0–14 days
Unvaccinated	128	62,331	2.05	Ref.		Ref.
Vaccinated - one dose	60	73,914	0.81	59.5	44.9 to 70.2	47.3	24.7 to 63.1
14–21 days
Unvaccinated	15	14,496	1.03	Ref.		Ref.
Vaccinated - one dose	6	36,600	0.16	84.1	59.1 to 93.8	84.1	39.7 to 95.8
≥ 21 days
Unvaccinated	26	91,259	0.28	Ref.		Ref.
Vaccinated - one dose	3	11,067	0.27	72.0	−27.8 to 93.9	85.4	−35.3 to 98.4
0–7 days
Unvaccinated	11	14,186	0.78	Ref.		Ref.
Vaccinated - two doses	0	35,596	0.00	NE		NE
≥ 7 days
Unvaccinated	15	77,073	0.19	Ref.		Ref.
Vaccinated - two doses	4	216,098	0.02	90.2	68.7 to 96.9	95.1	62.4 to 99.4
Symptomatic cases
0–14 days
Unvaccinated	89	62,331	1.43	Ref.		Ref.
Vaccinated - one dose	47	73,914	0.64	54.8	35.2 to 68.5	39.9	9.1 to 60.3
14–21 days
Unvaccinated	8	14,496	0.55	Ref.		Ref.
Vaccinated - one dose	4	36,600	0.11	80.1	34.0 to 94.0	83.3	14.8 to 96.7
≥ 21 days
Unvaccinated	19	91,259	0.21	Ref.		Ref.
Vaccinated - one dose	2	11,067	0.18	66.4	−153 to 95.5	65.9	−171 to 95.7
0–7 days
Unvaccinated	6	14,186	0.42	Ref.		Ref.
Vaccinated - two doses	0	35,596	0.00	NE		NE
≥ 7 days
Unvaccinated	13	77,073	0.17	Ref.		Ref.
Vaccinated - two doses	2	216,098	0.01	94.1	73.3 to 98.7	93.7	50.8 to 99.2

CI: confidence interval; COVID-19: coronavirus disease; NE: not estimable (no cases among vaccinated healthcare workers); PD: person-days; Ref.: reference category; VE: vaccine effectiveness.

^a The analysis of VE for the second dose of the Comirnaty vaccine was performed beginning with the observation period on 17 January 2021 (i.e. the date of the first administration of the second dose).

^b VE adjusted for sex, age group, professional category, work context, and starting week of exposure.

^C Asymptomatic and symptomatic COVID-19 cases.