Table 1 Baseline characteristics of the eligible and matched cohorts.

From: Effectiveness and durability of a fourth dose of ancestral-strain mRNA vaccines against SARS-CoV-2 infection: a nationwide matched cohort study in Qatar

Characteristics

Full eligible cohorts

Matched cohorts*

Four-dose cohort

Three-dose cohort†

SMD‡

Four-dose cohort

Three-dose cohort†

SMD‡

N = 9,673

N = 689,088

N = 7,463

N = 7,463

Median age (IQR) — years

61 (51–66)

40 (33–49)

1.31§

60 (50–66)

60 (50–65)

0.03§

Age group — no. (%)

0–9 years

0 (0.0)

2 (0.0)

1.38

--

--

0.00

10–19 years

15 (0.2)

33,383 (4.8)

8 (0.1)

8 (0.1)

20–29 years

171 (1.8)

68,014 (9.9)

136 (1.8)

136 (1.8)

30–39 years

1,003 (10.4)

227,474 (33.0)

843 (11.3)

843 (11.3)

40–49 years

1,051 (10.9)

197,382 (28.6)

809 (10.8)

809 (10.8)

50–59 years

2,278 (23.6)

106,293 (15.4)

1,859 (24.9)

1,859 (24.9)

60–69 years

3,775 (39.0)

43,589 (6.3)

2,926 (39.2)

2,926 (39.2)

70 + years

1,380 (14.3)

12,951 (1.9)

882 (11.8)

882 (11.8)

Sex

Male

7,194 (74.4)

451,000 (65.4)

0.20

5,723 (76.7)

5,723 (76.7)

0.00

Female

2,479 (25.6)

238,088 (34.6)

1,740 (23.3)

1,740 (23.3)

Nationality‖

Bangladeshi

912 (9.4)

60,218 (8.7)

0.27

786 (10.5)

786 (10.5)

0.00

Egyptian

543 (5.6)

55,717 (8.1)

406 (5.4)

406 (5.4)

Filipino

1,743 (18.0)

96,477 (14.0)

1,459 (19.5)

1,459 (19.5)

Indian

2,498 (25.8)

216,374 (31.4)

2,253 (30.2)

2,253 (30.2)

Nepalese

238 (2.5)

27,263 (4.0)

208 (2.8)

208 (2.8)

Pakistani

497 (5.1)

32,214 (4.7)

380 (5.1)

380 (5.1)

Qatari

413 (4.3)

41,370 (6.0)

368 (4.9)

368 (4.9)

Sri Lankan

168 (1.7)

19,984 (2.9)

110 (1.5)

110 (1.5)

Sudanese

211 (2.2)

12,333 (1.8)

155 (2.1)

155 (2.1)

Other nationalities

2,450 (25.3)

127,138 (18.5)

1,338 (17.9)

1,338 (17.9)

Coexisting conditions

0

3,987 (41.2)

517,328 (75.1)

0.79

3,430 (46.0)

3,430 (46.0)

0.00

1

1,433 (14.8)

77,285 (11.2)

1,089 (14.6)

1,089 (14.6)

2

1,370 (14.2)

43,906 (6.4)

1,036 (13.9)

1,036 (13.9)

3

999 (10.3)

22,462 (3.3)

705 (9.4)

705 (9.4)

4

778 (8.0)

13,384 (1.9)

514 (6.9)

514 (6.9)

5

554 (5.7)

7,573 (1.1)

339 (4.5)

339 (4.5)

≥ 6

552 (5.7)

7,150 (1.0)

350 (4.7)

350 (4.7)

Vaccine type

BNT162b2

7,750 (80.1)

447,676 (65.0)

0.34

5,947 (79.7)

5,947 (79.7)

0.00

mRNA-1273

1,923 (19.9)

241,412 (35.0)

1,516 (20.3)

1,516 (20.3)

Prior infection status**

No prior infection

7,200 (74.4)

--

--

6,049 (81.1)

6,049 (81.1)

0.00

Prior pre-omicron infection

1,159 (12.0)

--

704 (9.4)

704 (9.4)

Prior omicron infection

1,205 (12.5)

--

665 (8.9)

665 (8.9)

Prior pre-omicron & omicron infections

109 (1.1)

--

45 (0.6)

45 (0.6)

  1. IQR denotes interquartile range and SMD standardized mean difference.
  2. *Cohorts were matched one-to-one by sex, 10-year age group, nationality, number of coexisting conditions, vaccine type, prior infection status, and calendar week of the third vaccine dose.
  3. †This cohort includes everyone with at least three mRNA vaccine doses, therefore it also includes those who eventually received a fourth dose some time after the third dose.
  4. ‡SMD is the difference in the mean of a covariate between groups divided by the pooled standard deviation. An SMD < 0.1 indicates adequate matching.
  5. §SMD is for the mean difference between groups divided by the pooled standard deviation.
  6. ‖Nationalities were chosen to represent the most populous groups in Qatar.
  7. These comprise up to 163 other nationalities in the unmatched and 51 other nationalities in the matched cohorts.
  8. **Ascertained at the start of follow-up. Accordingly, distribution is not available for the unmatched three-dose cohort, as the start of follow-up for each person in the three-dose cohort is determined by that of their match in the four-dose cohort after the matching process is completed.
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