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Volume 28, Number 6—June 2022
Dispatch

Secondary Attack Rate, Transmission and Incubation Periods, and Serial Interval of SARS-CoV-2 Omicron Variant, Spain

Javier Del Águila-Mejía, Reinhard Wallmann, Jorge Calvo-Montes, Jesús Rodríguez-Lozano, Trinidad Valle-Madrazo, and Adrian Aginagalde-Llorente
Author affiliations: University Hospital of Móstoles, Madrid, Spain (J. Del Águila-Mejía); Public Health Observatory of Cantabria, Santander, Spain (J. Del Águila-Mejía, A. Aginagalde-Llorente); Directorate General of Public Health, Government of Cantabria, Santander (R. Wallmann); Marqués de Valdecilla University Hospital, Santander (J. Calvo-Montes, J. Rodríguez-Lozano, T. Valle-Madrazo)

Main Article

Table 1

Secondary attack rates of Omicron and Delta variant of SARS-CoV-2, by setting and vaccine status of the index case-patient, Spain*

Settings
 Omicron
Delta
 Difference, % (95% CI)
Index cases
 Close contacts
 Secondary cases
 SAR, %
(95% CI)
 Index cases
 Close contacts
 Secondary cases
 SAR, %
(95% CI)
Global 333 1,126 443 39.3
(36.5–42.2)		 1,403 7,013 1,846 26.3
(25.3–27.4)		 13†
(9.9–16.1)
Unvaccinated 
index case-patient 210 655 269 41.1
(37.4–44.9)		 535 2,876 895 31.1‡
(29.5–32.8)		 10†
(5.7–14.2)
Vaccinated index 
case-patient
 111
 436
 159
 36.5
(32.1–41.1)
829
 3,904
 910
 23.3‡
(22–24.7)
 13.2†
(8.3–18)
Household 287 533 263 49.4
(54–53.6)		 1,095 2,350 1,129 48
(46–50)		 1.3
(−3.4 to 6)
Unvaccinated 
index case-patient 187 354 171 49.4
(44.2–54.7)		 450 1,118 595 53.2‡
(50.3–56)		 −3.8
(−9.8 to 2.2)
Vaccinated index 
case-patient
 91
 171
 85
 49.7
(42.3–57)
622
 1,198
 519
 43‡
(40.5–46)
 6.4
(−1.6 to 14.4)
Social 143 524 160 30.5
(26.8–34.6)		 836 4,153 672 16.2
(15.1–17.3)		 14.4†
(10.3–18.5)
Unvaccinated 
index case-patient 76 283 88 31.1
(26–36.7)		 315 1,640 284 17.3
(15.6–19.2)		 13.8†
(7.9–19.7)
Vaccinated index 
case-patient
 61
 224
 64
 28.6
(23.1–34)
495
 2,351
 368
 15.7
(14.2–17.2)
 12.9†
(6.6–19.3)
Occupational 29 58 18 31
(20.6–43.8)		 148 411 43 10.5
(7.93–13.8)		 20.6†
(7.3–33.8)
Unvaccinated 
index case-patient 14 22 8 36.4
(19.7–57)		 39 97 16 16.5‡
(10.4–25.1)		 20.1
(−0.04 to 44.1)
Vaccinated index 
case-patient 14 34 10 29.4
(16.8–46.1)		 105 298 21 7‡
(4.7–10.5)		 22.4†
(5.1–40)

*SAR, secondary attack rate. †p<0.001. ‡Differences between vaccinated and unvaccinated persons within same-variant context.

Main Article

Page created: March 23, 2022
Page updated: May 22, 2022
Page reviewed: May 22, 2022
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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