SARS-CoV-2 seroprevalence among healthcare workers in a highly vaccinated Japanese medical center from 2020–2023

Figures & data

Figure 1. Seroprevalence at JUH with respect to the cumulative confirmed COVID-19 cases in the Tokyo metropolitan area.

Dots in the figure indicate seroprevalences at JUH, calculated by the number of N-specific positive HCWs divided by the number of HCWs who participated at annual health examinations with serological analysis.

A total of five mass vaccination campaigns were organized for HCWs at JUH, from March 2020 to November 2022, all using mRNA COVID-19 vaccines (BNT162b2 and mRNA-1273).

Table 1. N-specific antibody results among participants by characteristic categories (n = 3,594).

	Overall (%)	N-specific antibody positive, n (%)	N-specific antibody negative, n (%)	p-value^a
All	3594 (100)	1944 (54.1)	1650 (45.9)
Age (years)				<.001
20–29	989 (27.5)	606 (61.3)	383 (38.7)
30–39	1064 (29.6)	610 (57.3)	454 (42.7)
40–49	810 (22.5)	431 (53.2)	379 (46.8)
50–59	456 (12.7)	194 (42.5)	262 (57.5)
60 or older	275 (7.7)	103 (37.5)	172 (62.5)
Sex				.635
Male	1348 (37.5)	736 (54.6)	612 (45.4)
Female	2246 (62.5)	1208 (53.8)	1038 (46.2)
Profession				<.001
Medical doctors	920 (25.6)	508 (55.2)	412 (44.8)
Nurses	919 (25.6)	556 (60.5)	363 (39.5)
University teachers/researchers/ medical students	829 (23.1)	443 (53.4)	386 (46.6)
Administrative staff	570 (15.9)	283 (49.6)	287 (50.4)
Co-medical staff^b	356 (9.9)	154 (43.3)	202 (56.7)
No. of vaccine doses received^c				<.001
Unvaccinated	143 (4.0)	88 (61.5)	55 (38.5)
1 dose	39 (1.1)	31 (79.5)	8 (20.5)
2 doses	184 (5.1)	121 (65.8)	63 (34.2)
3 doses	691 (19.2)	453 (65.5)	238 (34.4)
4 doses	1169 (32.5)	648 (55.4)	521 (44.6)
5 doses	1216 (33.8)	548 (45.1)	668 (54.9)
6 doses	151 (4.2)	55 (36.4)	96 (63.6)
unknown	1 (0.0)	0 (0.0)	1 (100.0)
PCR-confirmed COVID-19 history (Yes/No)^d				<.001
No	2259 (62.9)	736 (32.6)	1523 (67.4)
Yes	1335 (37.1)	1208 (90.5)	127 (9.5)
1 time	1295	1169	126
2 times	39	38	1
3 times	1	1	0

^aChi square tests were applied for p values on percentages of N-specific antibody serological results (positive vs. negative) among the different groups of each category.

^bCo-medical staff include laboratory technicians, radiologists, rehabilitation specialists, pharmacists, and nutritionists.

^cGroup of “unknown” was not included in the chi square test.

^dChi square test was conducted among groups “No” and “Yes.” Detailed data of times of PCR-confirmed COVID-19 history were not included for the chi square test.

Table 2. Univariate and multivariate regression analyzes for seropositivity among participants (n = 3,594).

				Univariate regression			Multivariate regression
Parameter	Participants in all, n	N-specific antibody positive, n	N-specific antibody positive, %	OR	[95%CI]	p-value	Adjusted OR	[95%CI]	p-value
All	3594	1944	54.1%
Age
≥50 (reference)	731	297	40.6%
<50	2863	1647	57.5%	1.98	[1.68–2.34]	<.001	1.62	[1.36–1.93]	<.001
Sex
Male (reference)	1348	736	54.6%
Female	2246	1208	53.8%	0.97	[0.85–1.11]	.635	0.80	[0.69–0.93]	.004
Profession
Administrative/University staff ^a (reference)	1399	726	51.9%
Doctors	920	508	55.2%	1.14	[0.97–1.35]	.117	1.18	[0.99–1.40]	.065
Nurses	919	556	60.5%	1.42	[1.20–1.68]	<.001	1.48	[1.22–1.78]	<.001
Co-medical staff ^b	356	154	43.3%	0.71	[0.56–0.89]	.004	0.75	[0.59–0.95]	.017
No. of vaccine doses
5 or more (reference)	1367	603	44.1%
Unvaccinated	144	88	61.1%	1.99	[1.40–2.83]	<.001	1.88	[1.32–2.69]	.001
1 dose	39	31	79.5%	4.91	[2.24–10.76]	<.001	4.31	[1.96–9.47]	<.001
2 doses	184	121	65.8%	2.43	[1.76–3.36]	<.001	2.23	[1.61–3.10]	<.001
3 doses	691	453	65.6%	2.41	[2.00–2.92]	<.001	2.15	[1.76–2.61]	<.001
4 doses	1169	648	55.4%	1.58	[1.35–1.84]	<.001	1.45	[1.23–1.70]	<.001

^aUniversity staff include university teachers, researchers and medical students.

^bCo-medical staff include laboratory technicians, radiologists, rehabilitation specialists, pharmacists and nutritionists.

Data availability statement

All data used in the study are shown in the figures and tables. There are no more data to disclose.