1. Epidemiology and Global Health

Assessing healthy vaccinee effect in COVID-19 vaccine effectiveness studies: a national cohort study in Qatar

  1. Hiam Chemaitelly  Is a corresponding author
  2. Houssein H Ayoub
  3. Peter Coyle
  4. Patrick Tang
  5. Mohammad R Hasan
  6. Hadi M Yassine
  7. Asmaa A Al Thani
  8. Zaina Al-Kanaani
  9. Einas Al-Kuwari
  10. Andrew Jeremijenko
  11. Anvar Hassan Kaleeckal
  12. Ali Nizar Latif
  13. Riyazuddin Mohammad Shaik
  14. Hanan F Abdul-Rahim
  15. Gheyath K Nasrallah
  16. Mohamed Ghaith Al-Kuwari
  17. Hamad Eid Al-Romaihi
  18. Mohamed H Al-Thani
  19. Abdullatif Al-Khal
  20. Roberto Bertollini
  21. Adeel A Butt
  22. Laith J Abu-Raddad  Is a corresponding author
  1. Infectious Disease Epidemiology Group, Weill Cornell Medicine-Qatar, Cornell University, Qatar
  2. World Health Organization Collaborating Centre for Disease Epidemiology Analytics on HIV/AIDS, Sexually Transmitted Infections, and Viral Hepatitis, Weill Cornell Medicine-Qatar, Cornell University, Qatar Foundation – Education City, Qatar
  3. Department of Population Health Sciences, Weill Cornell Medicine, Cornell University, United States
  4. Mathematics Program, Department of Mathematics and Statistics, College of Arts and Sciences, Qatar University, Qatar
  5. Department of Biomedical Science, College of Health Sciences, QU Health, Qatar University, Qatar
  6. Hamad Medical Corporation, Qatar
  7. Wellcome-Wolfson Institute for Experimental Medicine, Queens University, United Kingdom
  8. Department of Pathology, Sidra Medicine, Qatar
  9. Department of Pathology and Molecular Medicine, McMaster University, Canada
  10. Biomedical Research Center, QU Health, Qatar University, Qatar
  11. Department of Public Health, College of Health Sciences, QU Health, Qatar University, Qatar
  12. Primary Health Care Corporation, Qatar
  13. Ministry of Public Health, Qatar
  14. Department of Medicine, Weill Cornell Medicine, Cornell University, United States
  15. College of Health and Life Sciences, Hamad bin Khalifa University, Qatar
https://doi.org/10.7554/eLife.103690
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Cite this article
  1. Hiam Chemaitelly
  2. Houssein H Ayoub
  3. Peter Coyle
  4. Patrick Tang
  5. Mohammad R Hasan
  6. Hadi M Yassine
  7. Asmaa A Al Thani
  8. Zaina Al-Kanaani
  9. Einas Al-Kuwari
  10. Andrew Jeremijenko
  11. Anvar Hassan Kaleeckal
  12. Ali Nizar Latif
  13. Riyazuddin Mohammad Shaik
  14. Hanan F Abdul-Rahim
  15. Gheyath K Nasrallah
  16. Mohamed Ghaith Al-Kuwari
  17. Hamad Eid Al-Romaihi
  18. Mohamed H Al-Thani
  19. Abdullatif Al-Khal
  20. Roberto Bertollini
  21. Adeel A Butt
  22. Laith J Abu-Raddad
(2025)
Assessing healthy vaccinee effect in COVID-19 vaccine effectiveness studies: a national cohort study in Qatar
eLife 14:e103690.
https://doi.org/10.7554/eLife.103690
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3 figures, 4 tables and 1 additional file

Figures

Figure 1 with 3 supplements
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Cumulative incidence of non-COVID-19 death in the matched (A) two-dose cohort compared to the unvaccinated cohort and (B) three-dose cohort compared to the two-dose cohort.
Figure 1—source data 1

Data used to generate Figure 1A and B.

https://cdn.elifesciences.org/articles/103690/elife-103690-fig1-data1-v1.xlsx
Figure 1—figure supplement 1
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Distribution of vaccinations.

Number of (A) second dose and (B) third dose vaccinations by calendar month.

Figure 1—figure supplement 2
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Flowchart describing the study population selection process for investigating an indication effect or a healthy vaccinee effect among recipients of primary series vaccination compared to those with no vaccination in Qatar.
Figure 1—figure supplement 3
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Flowchart describing the study population selection process for investigating an indication effect or a healthy vaccinee effect among recipients of booster (third dose) vaccination compared to recipients of primary series vaccination in Qatar.
Figure 2 with 1 supplement
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Adjusted hazard ratios for incidence of non-COVID-19 death in the (A) two-dose analysis and (B) three-dose analysis, by 6-month interval of follow-up.

Error bars indicate the corresponding 95% confidence intervals.

Figure 2—source data 1

Data used to generate Figure 2A and B.

https://cdn.elifesciences.org/articles/103690/elife-103690-fig2-data1-v1.xlsx
Figure 2—figure supplement 1
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Adjusted hazard ratios for incidence of severe, critical, or fatal COVID-19 in the two-dose and three-dose analyses, by 6-month interval of follow-up.

Error bars indicate the corresponding 95% confidence intervals.

Author response image 1
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Sensitivity analysis.

Adjusted hazard ratios for incidence of non-COVID-19 death in the entire population without matching on a SARS-CoV-2-negative test among controls. Results are shown for the (A) two-dose analysis and the (B) three-dose analysis, in the first 6 months of follow-up and the period thereafter.

Tables

Table 1
Baseline characteristics of the full and matched cohorts for investigating an indication effect or a healthy vaccinee effect among recipients of primary series or booster (third dose) vaccination in Qatar.
Two-dose analysisThree-dose analysis
CharacteristicsFull eligible cohortsMatched cohorts*Full eligible cohortsMatched cohorts†
Two-doseUnvaccinatedSMD‡Two-doseUnvaccinatedSMD‡Three-doseTwo-doseSMD‡Three-doseTwo-doseSMD‡
N=2,168,050N=3,811,694N=812,583N=812,583N=714,893N=2,231,443N=330,568N=330,568
Median age (IQR)—years38 (31–45)32 (24–41)0.50§34 (28–41)33 (27–40)0.07§40 (33–49)38 (31–45)0.21§38 (32–45)39 (34–47)0.01§
Age group—no. (%)
0–19 years106,156 (4.9)622,215 (16.3)0.5869,673 (8.6)69,673 (8.6)0.0033,216 (4.6)107,885 (4.8)0.239,221 (2.8)9,221 (2.8)0.00
20–29 years326,484 (15.1)909,809 (23.9)191,420 (23.6)191,420 (23.6)72,966 (10.2)334,458 (15.0)40,015 (12.1)40,015 (12.1)
30–39 years809,250 (37.3)1,228,030 (32.2)326,985 (40.2)326,985 (40.2)239,713 (33.5)834,373 (37.4)139,067 (42.1)139,067 (42.1)
40–49 years576,564 (26.6)660,453 (17.3)158,847 (19.5)158,847 (19.5)204,224 (28.6)595,300 (26.7)98,080 (29.7)98,080 (29.7)
50–59 years244,963 (11.3)268,839 (7.1)51,661 (6.4)51,661 (6.4)107,990 (15.1)252,382 (11.3)36,284 (11.0)36,284 (11.0)
60–69 years80,555 (3.7)92,395 (2.4)12,014 (1.5)12,014 (1.5)43,815 (6.1)82,558 (3.7)7,355 (2.2)7,355 (2.2)
70+ years24,078 (1.1)29,953 (0.8)1,983 (0.2)1,983 (0.2)12,969 (1.8)24,487 (1.1)546 (0.2)546 (0.2)
Sex
Male1,599,920 (73.8)2,682,394 (70.4)0.08593,856 (73.1)593,856 (73.1)0.00467,443 (65.4)1,645,973 (73.8)0.18245,116 (74.1)245,116 (74.1)0.00
Female568,130 (26.2)1,129,300 (29.6)218,727 (26.9)218,727 (26.9)247,450 (34.6)585,470 (26.2)85,452 (25.9)85,452 (25.9)
Nationality
Bangladeshi306,251 (14.1)269,021 (7.1)0.3068,102 (8.4)68,102 (8.4)0.0066,000 (9.2)312,475 (14.0)0.3937,670 (11.4)37,670 (11.4)0.00
Egyptian106,392 (4.9)184,152 (4.8)40,791 (5.0)40,791 (5.0)59,691 (8.3)109,910 (4.9)18,103 (5.5)18,103 (5.5)
Filipino201,002 (9.3)277,459 (7.3)76,146 (9.4)76,146 (9.4)99,405 (13.9)209,620 (9.4)40,680 (12.3)40,680 (12.3)
Indian531,366 (24.5)1,074,425 (28.2)268,830 (33.1)268,830 (33.1)222,135 (31.1)549,694 (24.6)121,774 (36.8)121,774 (36.8)
Nepalese233,558 (10.8)347,108 (9.1)68,279 (8.4)68,279 (8.4)28,584 (4.0)239,262 (10.7)20,694 (6.3)20,694 (6.3)
Pakistani103,600 (4.8)223,498 (5.9)46,416 (5.7)46,416 (5.7)34,161 (4.8)106,177 (4.8)14,548 (4.4)14,548 (4.4)
Qatari195,030 (9.0)319,209 (8.4)64,135 (7.9)64,135 (7.9)40,519 (5.7)199,550 (8.9)23,062 (7.0)23,062 (7.0)
Sri Lankan75,586 (3.5)127,750 (3.4)21,827 (2.7)21,827 (2.7)20,759 (2.9)77,913 (3.5)10,988 (3.3)10,988 (3.3)
Sudanese45,213 (2.1)78,528 (2.1)17,594 (2.2)17,594 (2.2)12,920 (1.8)46,586 (2.1)4,140 (1.3)4,140 (1.3)
Other nationalities**370,052 (17.1)910,544 (23.9)140,463 (17.3)140,463 (17.3)130,719 (18.3)380,256 (17.0)38,909 (11.8)38,909 (11.8)
Coexisting conditions
01,809,569 (83.5)3,352,859 (88.0)0.14746,840 (91.9)746,840 (91.9)0.00540,392 (75.6)1,860,263 (83.4)0.20311,376 (94.2)311,376 (94.2)0.00
1183,168 (8.4)261,898 (6.9)45,414 (5.6)45,414 (5.6)78,872 (11.0)189,770 (8.5)12,288 (3.7)12,288 (3.7)
286,673 (4.0)102,968 (2.7)13,988 (1.7)13,988 (1.7)44,676 (6.2)89,926 (4.0)5,049 (1.5)5,049 (1.5)
339,989 (1.8)42,960 (1.1)3,842 (0.5)3,842 (0.5)22,684 (3.2)41,422 (1.9)1,149 (0.3)1,149 (0.3)
422,810 (1.1)23,715 (0.6)1,602 (0.2)1,602 (0.2)13,504 (1.9)23,539 (1.1)558 (0.2)558 (0.2)
513,035 (0.6)13,575 (0.4)657 (0.1)657 (0.1)7,590 (1.1)13,415 (0.6)122 (<0.01)122 (<0.01)
≥612,806 (0.6)13,719 (0.4)240 (<0.01)240 (<0.01)7,175 (1.0)13,108 (0.6)26 (<0.01)26 (<0.01)
Prior infection status††
No prior infection1,957,313 (90.3)––764,366 (94.1)764,366 (94.1)0.00591,083 (82.7)––287,773 (87.1)287,773 (87.1)0.00
Prior pre-omicron infection208,058 (9.6)–46,631 (5.7)46,631 (5.7)96,567 (13.5)–33,864 (10.2)33,864 (10.2)
Prior omicron infection2,463 (0.1)–1,548 (0.2)1,548 (0.2)24,690 (3.5)–8,624 (2.6)8,624 (2.6)
Prior pre-omicron and omicron infections216 (<0.01)–38 (<0.01)38 (<0.01)2,553 (0.4)–307 (0.1)307 (0.1)

  1. IQR, interquartile range; SMD, standardized mean difference.

  2. *

    Cohorts were matched exactly one-to-one by sex, 10-year age group, nationality, type of coexisting conditions, and prior infection status. Persons who received their second vaccine dose in a specific calendar week in the two-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the unvaccinated cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  3. †

    Cohorts were matched exactly one-to-one by sex, 10-year age group, nationality, type of coexisting conditions, prior infection status, and calendar week of the second vaccine dose. Persons who received their third vaccine dose in a specific calendar week in the three-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the two-dose cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  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 183 other nationalities in the unmatched and 148 other nationalities in the matched two-dose analyses, and up to 169 other nationalities in the unmatched and 111 other nationalities in the matched three-dose analyses.

  8. ††

    Ascertained at the start of follow-up. Accordingly, distribution is not available for the unmatched unvaccinated cohort in the two-dose analysis and unmatched two-dose cohort in the three-dose analysis, as the start of follow-up for each person in these reference/control cohorts is determined by that of their match after the matching process is completed.

Table 2
Hazard ratios for incidence of non-COVID-19 death, SARS-CoV-2 infection, and severe, critical, or fatal COVID-19 in the (A) two-dose analysis and (B) three-dose analysis.
(A) Two-dose analysisTwo-dose cohort*Unvaccinated cohort*
Sample size812,583812,583
Number of non-COVID-19 death237306
Number of incident infections54,42757,974
Number of severe, critical, or fatal COVID-19 disease29630
Total follow-up time (person-weeks)46,028,31846,275,391
Non-COVID-19 death  
Incidence rate of non-COVID-19 death (per 10,000 person-weeks; 95% CI)0.05 (0.05–0.06)0.07 (0.06–0.07)
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.77 (0.65–0.91)
Adjusted hazard ratio for non-COVID-19 death (95% CI)†0.76 (0.64–0.90)
SARS-CoV-2 infection 
Unadjusted hazard ratio for SARS-CoV-2 infection (95% CI)0.93 (0.92–0.94)
Adjusted hazard ratio for SARS-CoV-2 infection (95% CI)‡0.89 (0.88–0.90)
Effectiveness against SARS-CoV-2 infection (95% CI)‡10.7 (9.6–11.7)
Severe, critical, or fatal COVID-19 disease 
Unadjusted hazard ratio for severe, critical, or fatal COVID-19 disease (95% CI)0.05 (0.03–0.07)
Adjusted hazard ratio for severe, critical, or fatal COVID-19 disease (95% CI)‡0.04 (0.03–0.06)
Effectiveness against severe, critical, or fatal COVID-19 disease (95% CI)‡95.9 (94.0–97.1)
(B) Three-dose analysisThree-dose cohort§Two-dose cohort§
Sample size330,568330,568
Number of non-COVID-19 death132147
Number of incident infections26,84235,411
Number of severe, critical, or fatal COVID-19 disease69
Total follow-up time (person-weeks)24,015,30723,088,912
Non-COVID-19 death  
Incidence rate of non-COVID-19 death (per 10,000 person-weeks; 95% CI)0.05 (0.05–0.07)0.06 (0.05–0.07)
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.87 (0.68–1.10)
Adjusted hazard ratio for non-COVID-19 death (95% CI)0.85 (0.67–1.07)
SARS-CoV-2 infection 
Unadjusted hazard ratio for SARS-CoV-2 infection (95% CI)0.74 (0.72–0.75)
Adjusted hazard ratio for SARS-CoV-2 infection (95% CI)**0.74 (0.72–0.75)
Effectiveness against SARS-CoV-2 infection (95% CI)**26.3 (25.2–27.5)
Severe, critical, or fatal COVID-19 disease 
Unadjusted hazard ratio for severe, critical, or fatal COVID-19 disease (95% CI)0.64 (0.23–1.81)
Adjusted hazard ratio for severe, critical, or fatal COVID-19 disease (95% CI)**0.66 (0.23–1.86)
Effectiveness against severe, critical, or fatal COVID-19 disease (95% CI)**34.1 (−46.4–76.7)

  1. CI, confidence interval; COVID-19, coronavirus disease 2019; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

  2. *

    Cohorts were matched exactly one-to-one by sex, 10-year age group, nationality, type of coexisting conditions, and prior infection status. Persons who received their second vaccine dose in a specific calendar week in the two-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the unvaccinated cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  3. †

    Adjusted for sex, 10-year age group, nationality, number of coexisting conditions, prior infection status, and calendar week of the second vaccine dose for the two-dose cohort or SARS-CoV-2-negative test for the unvaccinated cohort.

  4. ‡

    Adjusted for sex, 10-year age group, nationality, number of coexisting conditions, prior infection status, calendar week of the second vaccine dose for the two-dose cohort or SARS-CoV-2-negative test for the unvaccinated cohort, and testing rate.

  5. §

    Cohorts were matched exactly one-to-one by sex, 10-year age group, nationality, type of coexisting conditions, prior infection status, and calendar week of the second vaccine dose. Persons who received their third vaccine dose in a specific calendar week in the three-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the two-dose cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  6. Adjusted for sex, 10-year age group, nationality, number of coexisting conditions, prior infection status, and calendar week of the second vaccine dose.

  7. **

    Adjusted for sex, 10-year age group, nationality, number of coexisting conditions, prior infection status, calendar week of the second vaccine dose, and testing rate.

Table 3
Subgroup analyses.

Hazard ratios for incidence of non-COVID-19 death stratified by age group, clinical vulnerability status, and prior infection status in the (A) two-dose analysis and (B) three-dose analysis.

(A) Two-dose analysisTwo-dose cohort*Unvaccinated cohort*
Age
<50 years of age
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.91 (0.73–1.12)
Adjusted hazard ratio for non-COVID-19 death (95% CI)†0.89 (0.72–1.11)
≥50 years of age
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.59 (0.44–0.78)
Adjusted hazard ratio for non-COVID-19 death (95% CI)†0.56 (0.42–0.75)
Clinical vulnerability status
Less clinically vulnerable to severe COVID-19
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.99 (0.80–1.23)
Adjusted hazard ratio for non-COVID-19 death (95% CI)†0.98 (0.79–1.22)
More clinically vulnerable to severe COVID-19
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.53 (0.41–0.70)
Adjusted hazard ratio for non-COVID-19 death (95% CI)†0.51 (0.39–0.68)
Prior infection status
No prior infection
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.76 (0.64–0.90)
Adjusted hazard ratio for non-COVID-19 death (95% CI)†0.74 (0.63–0.89)
Prior pre-omicron infection
Unadjusted hazard ratio for non-COVID-19 death (95% CI)1.05 (0.48–2.30)
Adjusted hazard ratio for non-COVID-19 death (95% CI)†1.00 (0.45–2.20)
Prior omicron infection
Unadjusted hazard ratio for non-COVID-19 death (95% CI)-- ‡
Adjusted hazard ratio for non-COVID-19 death (95% CI)†-- ‡
Prior pre-omicron & omicron infections
Unadjusted hazard ratio for non-COVID-19 death (95% CI)-- ‡
Adjusted hazard ratio for non-COVID-19 death (95% CI)†-- ‡
(B) Three-dose analysisThree-dose cohort §Two-dose cohort §
Age
<50 years of age
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.90 (0.67–1.21)
Adjusted hazard ratio for non-COVID-19 death (95% CI)0.90 (0.67–1.20)
≥50 years of age
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.80 (0.54–1.18)
Adjusted hazard ratio for non-COVID-19 death (95% CI)0.76 (0.51–1.13)
Clinical vulnerability status
Less clinically vulnerable to severe COVID-19
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.91 (0.68–1.23)
Adjusted hazard ratio for non-COVID-19 death (95% CI)0.91 (0.67–1.22)
More clinically vulnerable to severe COVID-19
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.78 (0.54–1.15)
Adjusted hazard ratio for non-COVID-19 death (95% CI)0.76 (0.52–1.12)
Prior infection status
No prior infection
Unadjusted hazard ratio for non-COVID-19 death (95% CI)0.80 (0.63–1.03)
Adjusted hazard ratio for non-COVID-19 death (95% CI)0.79 (0.61–1.01)
Prior pre-omicron infection
Unadjusted hazard ratio for non-COVID-19 death (95% CI)1.63 (0.71–3.73)
Adjusted hazard ratio for non-COVID-19 death (95% CI)1.63 (0.71–3.72)
Prior omicron infection
Unadjusted hazard ratio for non-COVID-19 death (95% CI)1.32 (0.30–5.90)
Adjusted hazard ratio for non-COVID-19 death (95% CI)1.32 (0.30–5.91)
Prior pre-omicron & omicron infections
Unadjusted hazard ratio for non-COVID-19 death (95% CI)-- ‡
Adjusted hazard ratio for non-COVID-19 death (95% CI)-- ‡

  1. CI, confidence interval; COVID-19, coronavirus disease 2019; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

  2. *

    Cohorts were matched exactly one-to-one by sex, 10-year age group, nationality, type of coexisting conditions, and prior infection status. Persons who received their second vaccine dose in a specific calendar week in the two-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the unvaccinated cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  3. †

    Adjusted for sex, 10-year age group, nationality, number of coexisting conditions, prior infection status (where applicable), and calendar week of the second vaccine dose for the two-dose cohort or SARS-CoV-2-negative test for the unvaccinated cohort.

  4. ‡

    Could not be estimated because of no or small number of events.

  5. §

    Cohorts were matched exactly one-to-one by sex, 10-year age group, nationality, type of coexisting conditions, prior infection status, and calendar week of the second vaccine dose. Persons who received their third vaccine dose in a specific calendar week in the three-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the two-dose cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  6. Adjusted for sex, 10-year age group, nationality, number of coexisting conditions, prior infection status (where applicable), and calendar week of the second vaccine dose.

Table 4
Sensitivity analyses.

Hazard ratios for incidence of non-COVID-19 death among Qataris with and without matching on a SARS-CoV-2-negative test among controls in the (A) two-dose analysis and (B) three-dose analysis.

(A) Two-dose analysisTwo-dose cohortUnvaccinated cohort
Sensitivity analysis I-Restricting analysis to Qataris*
Unadjusted hazard ratiofor non-COVID-19 death (95% CI)0.29 (0.19–0.43)
Adjusted hazard ratiofor non-COVID-19 death (95% CI)†0.29 (0.19–0.43)
Sensitivity analysis II-Restricting analysis to Qataris and not matching by a SARS-CoV-2-negative test among controls‡
Unadjusted hazard ratiofor non-COVID-19 death (95% CI)0.40 (0.31–0.51)
Adjusted hazard ratiofor non-COVID-19 death (95% CI)§0.38 (0.30–0.50)
(B) Three-dose analysisThree-dose cohortTwo-dose cohort
Sensitivity analysis I-Restricting analysis to Qataris
Unadjusted hazard ratiofor non-COVID-19 death (95% CI)0.77 (0.44–1.33)
Adjusted hazard ratiofor non-COVID-19 death (95% CI)**0.76 (0.43–1.32)
Sensitivity analysis II-Restricting analysis to Qataris and not matching by a SARS-CoV-2-negative test among controls††
Unadjusted hazard ratiofor non-COVID-19 death (95% CI)0.77 (0.52–1.12)
Adjusted hazard ratiofor non-COVID-19 death (95% CI)**0.77 (0.53–1.13)

  1. CI, confidence interval; COVID-19, coronavirus disease 2019; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

  2. *

    Cohorts were matched exactly one-to-one by sex, 10-year age group, type of coexisting conditions, and prior infection status. Persons who received their second vaccine dose in a specific calendar week in the two-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the unvaccinated cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  3. †

    Adjusted for sex, 10-year age group, number of coexisting conditions, prior infection status, and calendar week of the second vaccine dose for the two-dose cohort or SARS-CoV-2-negative test for the unvaccinated cohort.

  4. ‡

    Cohorts were matched exactly one-to-one by sex, 10-year age group, type of coexisting conditions, and prior infection status.

  5. §

    Adjusted for sex, 10-year age group, number of coexisting conditions, and prior infection status.

  6. Cohorts were matched exactly one-to-one by sex, 10-year age group, type of coexisting conditions, prior infection status, and calendar week of the second vaccine dose. Persons who received their third vaccine dose in a specific calendar week in the three-dose cohort were additionally matched to persons who had a record for a SARS-CoV-2-negative test in that same calendar week in the two-dose cohort, to ensure that matched pairs had presence in Qatar over the same time period.

  7. **

    Adjusted for sex, 10-year age group, number of coexisting conditions, prior infection status, and calendar week of the second vaccine dose.

  8. ††

    Cohorts were matched exactly one-to-one by sex, 10-year age group, type of coexisting conditions, prior infection status, and calendar week of the second vaccine dose.

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  1. Hiam Chemaitelly
  2. Houssein H Ayoub
  3. Peter Coyle
  4. Patrick Tang
  5. Mohammad R Hasan
  6. Hadi M Yassine
  7. Asmaa A Al Thani
  8. Zaina Al-Kanaani
  9. Einas Al-Kuwari
  10. Andrew Jeremijenko
  11. Anvar Hassan Kaleeckal
  12. Ali Nizar Latif
  13. Riyazuddin Mohammad Shaik
  14. Hanan F Abdul-Rahim
  15. Gheyath K Nasrallah
  16. Mohamed Ghaith Al-Kuwari
  17. Hamad Eid Al-Romaihi
  18. Mohamed H Al-Thani
  19. Abdullatif Al-Khal
  20. Roberto Bertollini
  21. Adeel A Butt
  22. Laith J Abu-Raddad
(2025)
Assessing healthy vaccinee effect in COVID-19 vaccine effectiveness studies: a national cohort study in Qatar
eLife 14:e103690.
https://doi.org/10.7554/eLife.103690