Figure 1. COVID-19 vaccine uptake (%) of HCWs of ASUGI, by number of vaccine doses and calendar month (1 December 2021–31 May 2022).

Figure 1. COVID-19 vaccine uptake (%) of HCWs of ASUGI, by number of vaccine doses and calendar month (1 December 2021–31 May 2022).

Figure 2. Number of primary SARS-CoV-2 infections (N = 3571) in health care workers in ASUGI, by calendar month, 1 March 2020–31 May 2022.

Figure 2. Number of primary SARS-CoV-2 infections (N = 3571) in health care workers in ASUGI, by calendar month, 1 March 2020–31 May 2022.

Figure 3. Number of SARS-CoV-2 re-infections (Total = 406) in health care workers (HCWs) of ASUGI, by calendar month, 1 March 2020–31 May 2022.

Figure 3. Number of SARS-CoV-2 re-infections (Total = 406) in health care workers (HCWs) of ASUGI, by calendar month, 1 March 2020–31 May 2022.

Figure 4. (Kaplan-Meier survival curve). SARS-CoV-2 primary infections (N = 2130) occurred in healthcare workers (HCWs) of ASUGI from 1 December 2021–31 May 2022, by number of doses of COVID-19 vaccines received 7+ days (14+ days in case of only one dose) before infection. Number of HCWs at risk by number of doses of COVID-19 vaccine received.

Figure 4. (Kaplan-Meier survival curve). SARS-CoV-2 primary infections (N = 2130) occurred in healthcare workers (HCWs) of ASUGI from 1 December 2021–31 May 2022, by number of doses of COVID-19 vaccines received 7+ days (14+ days in case of only one dose) before infection. Number of HCWs at risk by number of doses of COVID-19 vaccine received.

Figure 5. (Kaplan-Meier survival curve). SARS-CoV-2 re-infections (N = 386) in healthcare workers of ASUGI between 1 December 2021–31 May 2022, by number of doses of COVID-19 vaccines received 7+ days (14+ days in case of only one dose) before re-infection. Number of HCWs at risk by number of doses of COVID-19 vaccine received.

Figure 5. (Kaplan-Meier survival curve). SARS-CoV-2 re-infections (N = 386) in healthcare workers of ASUGI between 1 December 2021–31 May 2022, by number of doses of COVID-19 vaccines received 7+ days (14+ days in case of only one dose) before re-infection. Number of HCWs at risk by number of doses of COVID-19 vaccine received.

Table 1. Distribution of variables. Number (N), percentage (%), mean ± standard deviation (SD), median and interquartile range (IQR).

Table 1. Distribution of variables. Number (N), percentage (%), mean ± standard deviation (SD), median and interquartile range (IQR).

FACTORSTRATANUMBERCol %SexFemale530868.7Male241531.3Age
(years)Mean ± SD46.6 ± 12.0 Median (IQR)48.6 (36.2; 56.7) <41246832.041–50175122.751–60245331.861+105113.6ASUGI
SiteGorizia-Monfalcone258933.5Trieste513466.5Incident
SARS-CoV-2
infections
(Total = 3541)TOTAL (1 Mar 2020–31 May 2022)3571100I (1 Mar 2020–31 May 2020)2146.0II (1 Jun 2020–30 Sep 2020)160.5III (1 Oct 2020–31 Dec 2020)53515.0IVa (1 Jan 2021–31 Mar 2021)2948.2IVb (1 Apr 2021–30 Sep 2021)1073.0V (1 Oct 2021–30 Nov 2021)2757.7VI (1 Dec 2021–31 May 2022)213059.7SARS-CoV-2
re-infections
(Tot = 406)TOTAL (1 Mar 2020–31 May 2022)406100I (1 Mar 2020–31 May 2020)00II (1 Jun 2020–30 Sep 2020)20.5III (1 Oct 2020–31 Dec 2020)41.0IVa (1 Jan 2021–31 Mar 2021)2 0.5IVb (1 Apr 2021–30 Sep 2021)51.2V (1 Oct 2021–30 Nov 2021)71.7VI (1 Dec 2021–31 May 2022)38695.1Number of swab tests
(1 December 2021–
31 May 2022)06027.81–375410.64–6118916.77–10175924.711+341948.0Number of doses of COVID-19 Vaccine
(by 31 May 2022)TOTAL772310006087.911862.4286811.23604778.34140.2Vaccine
typeComirnaty (Pfitzer/BioNTech)7388 95.7Spikevax (Moderna)3064.0Vaxzevria (Oxford-Astra Zeneca; N = 21)290.4Janssen (Johnson & Johnson; N = 7)Nuvaxovid (Novavax; N = 1)Job taskTOTAL7723100Administrative6288.1Doctor1567 20.3Nurses273335.4Other HCWs164221.3Technician115314.9Educational level
(Missing: 1880)TOTAL5843100Junior secondary273346.8Secondary3806.5Bachelor’s degree108518.6Postgraduate diploma164528.2WorkplaceTOTAL7723100Administrative services935 12.1Community services2339 30.3Radiology services (technician)5627.3Surgical ward116715.1Medical and geriatric ward144918.8COVID-19 area2453.2Accident and emergency (A&E)7579.8Non-clinical workers and other2693.5

Table 2. COVID-19 vaccination coverage of health care workers of ASUGI, by number of doses and calendar month, 1 December 2021–31 May 2022. Number and percentage (%).

Table 2. COVID-19 vaccination coverage of health care workers of ASUGI, by number of doses and calendar month, 1 December 2021–31 May 2022. Number and percentage (%).

DATE0 Doses1 Dose2 Doses3 Doses4 Doses1 December 2021773 (10.0)461 (6.0)2876 (37.2)3613 (46.8) 01 January 2022667 (8.6)395 (5.1)1500 (19.4) 5161 (66.8) 01 February 2022635 (8.2)282 (3.7) 1204 (15.6) 5602 (72.5) 01 March 2022638 (8.3)233 (3.0) 1113 (14.4) 5739 (74.3) 01 April 2022626 (8.1)208 (2.7) 1082 (14.0) 5801 (75.1) 61 May 2022616 (8.0)194 (2.5) 920 (11.9) 5984 (77.5) 931 May 2022613 (7.9)186 (2.4) 868 (11.2) 6047 (78.3)9

Table 3. Crude incidence rates of primary and recurrent SARS-CoV-2 infections during 1 December 2021-31 May 2022, by number of doses of COVID-19 vaccine received 7+ days (14+ days in case of only one dose) before infection. Number of cases, person-days (p-d) at risk and raw incidence (×1000 p-d).

Table 3. Crude incidence rates of primary and recurrent SARS-CoV-2 infections during 1 December 2021-31 May 2022, by number of doses of COVID-19 vaccine received 7+ days (14+ days in case of only one dose) before infection. Number of cases, person-days (p-d) at risk and raw incidence (×1000 p-d).

FactorsType of
SARS-CoV-2 Infection
(01/12/2021–31/05/2022)Analysis TimeCasesPerson-Days (p-d)
at RiskRaw Incidence
(×1000 p-d)Total SARS-CoV-2
infectionsPrimary21302197819.7 × 1000 RecurrentTotal386107,9393.6 × 1000Primary infection before 01/12/202135439,7618.9 × 1000Primary infection after 30/11/20213268,1780.5 × 1000Doses of
COVID-19
vaccines0Primary18713,18314.2 × 1000RecurrentTotal9312,1997.6 × 1000Primary infection before 01/12/202173597312.2 × 1000Primary infection after 30/11/20212062263.2 × 10001Primary3962686.2 × 1000RecurrentTotal2968034.3 × 1000Primary infection before 01/12/202129254411.4 × 1000Primary infection after 30/11/20210399302Primary17714,20712.5 × 1000RecurrentTotal10619,6945.4 × 1000Primary infection before 01/12/202110212,7268.0 × 1000Primary infection after 30/11/2021469680.6 × 10003Primary1680184,7199.1 × 1000RecurrentTotal14168,5582.1 × 1000Primary infection before 01/12/202113317,8337.5 × 1000Primary infection after 30/11/2021850,7250.2 × 1000

Table 4. Cox proportional regression model for the risk of primary SARS-CoV-2 infection (1 December 2021–31 May 2022). Hazard ratio unadjusted (HR) and adjusted (aHR), with 95% confidence interval (95%CI). Multivariable model fitted onto 1994 complete observations. HCWs never tested for SARS-CoV-2 during 1 January–31 May 2022 (N = 602) were excluded from the analysis.

Table 4. Cox proportional regression model for the risk of primary SARS-CoV-2 infection (1 December 2021–31 May 2022). Hazard ratio unadjusted (HR) and adjusted (aHR), with 95% confidence interval (95%CI). Multivariable model fitted onto 1994 complete observations. HCWs never tested for SARS-CoV-2 during 1 January–31 May 2022 (N = 602) were excluded from the analysis.

FactorStrataCox Regression AnalysisUnivariable
HR (95%CI)Multivariable
aHR (95%CI)SexFemaleReferenceReferenceMale0.87 (0.80; 0.96)0.93 (0.83; 1.04)Age
(years) <41Reference 41–501.27 (1.14; 1.42)51–601.11 (1.00; 1.24)61+0.84 (0.72; 0.97)ASUGI siteGorizia-MonfalconeReferenceTrieste0.92 (0.84; 1.00)Vaccine typeComirnaty (Pfitzer/BioNTech)ReferenceSpikevax (Moderna)0.92 (0.73; 1.16)Other *0.68 (0.30; 1.51)N. Doses of
COVID-19
vaccines0Reference10.41 (0.29; 0.58)20.85 (0.69; 1.04)30.58 (0.50; 0.67)N. Swab tests
(1 Dec 2021–
31 May 2022)1–3ReferenceCOVID-19
vaccine
doses0Reference14.15 −10 (1.57−10; 1.09−9)20.59 (0.23; 1.49)30.47 (0.21; 1.08)4–61.27 (1.03; 1.56)COVID-19
vaccine
doses00.87 (0.37; 2.04)10.36 (0.11; 1.16)20.74 (0.32; 1.73)30.65 (0.30; 1.42)7–101.40 (1.16; 1.69)COVID-19
vaccine
doses01.16 (0.51; 2.64)10.30 (0.09; 0.96)20.85 (0.38; 1.93)30.58 (0.27; 1.24)10+0.96 (0.80; 1.15)COVID-19
vaccine
doses00.88 (0.40; 1.95)10.34 (0.14; 0.84)20.65 (0.29; 1.47)30.41 (0.15; 1.11)Job taskAdministrative clerksReferenceYears
of age<41Reference41–502.55 (1.45; 4.49)51–602.28 (1.41; 3.67)61+1.07 (0.61; 1.89)Doctor1.16 (0.97; 1.38)Years
of age<411.29 (0.84; 1.99)41–502.46 (1.62; 3.73)51–602.31 (1.45; 3.68)61+1.70 (1.02; 2.84)Nurses1.39 (1.18; 1.64)Years
of age<413.12 (2.11; 4.61)41–503.01 (2.00; 4.52)51–602.21 (1.46; 3.37)61+2.08 (1.22; 3.53)Other HCWs1.39 (1.16; 1.65)Years
of age<412.70 (1.74; 4.20)41–502.84 (1.87; 4.33)51–602.30 (1.51; 3.49)61+2.52 (1.55; 4.10)Health technicians1.20 (0.99; 1.44)Years
of age<412.38 (1.59; 3.56)41–502.78 (1.80; 4.30)51–601.97 (1.26; 3.09)61+1.66 (0.96; 2.87)WorkplaceAdministrative servicesReferenceReferenceCommunity health services1.42 (1.22; 1.65)1.18 (0.98; 1.43)Radiology services (technicians)1.48 (1.21; 1.82)1.58 (1.26; 1.97)Surgical wards1.34 (1.13; 1.59)1.43 (1.17; 1.76)Medical and geriatric wards1.28 (1.09; 1.50)1.34 (1.11; 1.63)COVID-19 areas1.04 (0.78; 1.40)1.07 (0.78; 1.47)Accident and emergency (A&E)1.25 (1.04 1.50)1.28 (1.03; 1.59)Non-clinical and other1.32 (1.01; 1.71)1.12 (0.79; 1.59)Years of employment (linear term) 1.01 (1.01; 1.01)1.01 (1.01; 1.02)Educational
levelJunior secondaryReference Secondary0.77 (0.62; 0.95)Bachelor’s degree1.01 (0.88; 1.15)Postgraduate diploma0.85 (0.75; 0.95)

Table 5. Cox proportional regression model for the risk of SARS-CoV-2 re-infections (1 December 2021–31 May 2022). Hazard ratio unadjusted (HR) and adjusted (aHR), with 95% confidence interval (95%CI). Multiple model fitted onto 731 complete case (analysis) observations. HCWs never tested for SARS-CoV-2 during 1 January-31 May 2022 (N = 602) were excluded from the analysis.

Table 5. Cox proportional regression model for the risk of SARS-CoV-2 re-infections (1 December 2021–31 May 2022). Hazard ratio unadjusted (HR) and adjusted (aHR), with 95% confidence interval (95%CI). Multiple model fitted onto 731 complete case (analysis) observations. HCWs never tested for SARS-CoV-2 during 1 January-31 May 2022 (N = 602) were excluded from the analysis.

FactorStrataCox Regression AnalysisUnivariable
HR (95%CI)Multivariable
aHR (95%CI)SexFemaleReferenceReferenceMale0.71 (0.57; 0.89)0.75 (0.59; 0.96)Age
(years)<41Reference 41–501.97 (1.54; 2.52)51–602.21 (1.72; 2.84)61+0.64 (0.39; 1.06)ASUGI
SiteGorizia-MonfalconeReferenceTrieste1.00 (0.79; 1.24)Vaccine
typeComirnaty (Pfitzer/BioNTech)ReferenceSpikevax (Moderna)1.07 (0.68; 1.70)Other *135.78 (16.34; 1127.95)Doses
of COVID-19
vaccines0ReferenceReference10.66 (0.43; 1.00)0.95 (0.59; 1.54)20.85 (0.65; 1.12)1.04 (0.76; 1.43)30.34 (0.26; 0.44)0.58 (0.42; 0.81)Swab tests
(1 December 2021–
31 May 2022)1–3ReferenceReference4–63.49 (1.50; 8.09)2.20 (0.67; 7.29)7–105.02 (2.21; 11.40)2.27 (0.69; 7.41)11+4.46 (1.98; 10.06)1.49 (0.46; 4.86)JOB TASKAdministrative clerksReferenceYears of age<41Reference41–504.11 (1.29; 13.09)51–602.29 (0.69; 7.65)61+4.27 (1.05; 17.41)Doctor1.79 (1.08; 2.97)Years of age<411.84 (0.72; 4.71)41–503.20 (1.20; 8.52)51–604.32 (1.50; 12.39)61+1.73 (0.39; 7.58)Nurses3.80 (2.43; 5.95)Years of age<417.47 (3.26; 17.10)41–505.33 (2.22; 12.79)51–602.73 (1.09; 6.84)61+13.51 (3.20; 57.04)Other HCWs3.51 (2.21; 5.56)Years of age<414.57 (1.87; 11.15)41–504.70 (1.97; 11.22)51–605.01 (2.07; 12.17)61+1.12 (0.22; 5.57)Health technician1.72 (1.05; 2.82)Years of age<412.32 (0.99; 5.44)41–503.89 (1.47; 10.26)51–602.28 (0.76; 6.84)61+3.50 (0.91; 13.54)WORKPLACEAdminis