Table 1. Effect of mRNA vaccines in preventing COVID-19 severe pneumonia among COVID-19 patients in Japan.

	Primary outcome COVID-19 severe pneumonia		Secondary outcome COVID-19 pneumonia

	case/Total (%)	Adjusted RR (95% CI)^a	case/Total (%)	Adjusted RR (95% CI)^a
Overall
Unvaccinated	95/2,252 (4.2)	1.0 (reference)	185/2,252 (8.2)	1.0 (reference)
Partially vaccinated	15/291 (5.2)	0.53 (0.30–0.94)	28/291 (9.6)	0.53 (0.35–0.79)
Fully vaccinated	4/149 (2.7)	0.25 (0.09–0.67)	8/149 (5.4)	0.25 (0.13–0.50)
Stratified analysis
Age group
<50 years old
Unvaccinated	55/1,915 (2.9)	1.0 (ref)	109/1,915 (5.7)	1.0 (ref)
Partially vaccinated	4/165 (2.4)	0.51 (0.16–1.61)	9/165 (5.5)	0.67 (0.33–1.37)
Fully vaccinated	0/63 (0.0)	NA	0/63 (0.0)	NA
≥50 years old
Unvaccinated	40/337 (11.9)	1.0 (ref)	76/337 (22.6)	1.0 (ref)
Partially vaccinated	11/126 (8.7)	0.54 (0.29–1.03)	19/126 (15.1)	0.49 (0.31–0.80)
Fully vaccinated	4/86 (4.7)	0.33 (0.12–0.91)	8/86 (9.3)	0.36 (0.18–0.72)
Comorbidity^b
None
Unvaccinated	30/1,474 (2.0)	1.0 (ref)	71/1,474 (4.8)	1.0 (ref)
Partially vaccinated	3/140 (2.1)	0.60 (0.18–2.06)	5/140 (3.6)	0.44 (0.18–1.10)
Fully vaccinated	1/74 (1.4)	0.31 (0.05–2.06)	3/74 (4.1)	0.40 (0.14–1.14)
More than one
Unvaccinated	63/731 (8.6)	1.0 (ref)	113/731 (15.5)	1.0 (ref)
Partially vaccinated	10/145 (6.9)	0.58 (0.30–1.11)	19/145 (13.1)	0.62 (0.40–0.97)
Fully vaccinated	3/72 (4.2)	0.26 (0.09–0.76)	5/72 (6.9)	0.21 (0.10–0.47)

BMI, body mass index; CI, confidence interval; COVID-19, coronavirus disease 2019; NA, not available; RR, risk ratio.

^aAdjusted for age category (20–39, 40–59, 60–79, and ≥80 years), sex, smoking status, hypertension, diabetes, heart disease, respiratory disease, and obesity (BMI ≥25 kg/m²). A total of 56 participants had missing BMI information.

^bComorbidities: hypertension, diabetes, heart disease, respiratory disease, and obesity. RRs were estimated by adjusting for age category, sex, and smoking status. A total of 56 participants had missing BMI information.