Table 3.
Effectiveness of COVID-19 vaccination during pregnancy against infant SARS-CoV-2 infection by infant age at testing, trimester of vaccination during pregnancy, and by virus variant: cohort design
| First 2 months of life | First 4 months of life | First 6 months of life | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Infant observation period by predominant SARS-CoV-2 variant, and mother’s vaccination status | Positive test N | Crude incidence ratea | Adjustedb VE (95% CI) | Positive test N | Crude incidence ratea | Adjustedb VE (95% CI) | Positive test N | Crude incidence ratea | Adjustedb VE (95% CI) |
| Delta period | |||||||||
| Unvaccinated during pregnancy | 54 | 5.47 | Reference | 118 | 5.10 | Reference | 190 | 4.78 | Reference |
| Received ≥2 doses during pregnancy | |||||||||
| Second dose during the first trimester | 3 | 1.73 | 62 (−23,89) | 4 | 1.80 | 46 (−36, 82) | 4 | 1.78 | 47 (−34, 81) |
| Second dose during the second trimester | 2 | 0.42 | 91 (63,98) | 11 | 1.39 | 59 (21,79) | 11 | 1.23 | 64 (31,81) |
| Second dose during the third trimester | 3 | 0.72 | 85 (50,96) | 12 | 1.37 | 67 (37,83) | 22 | 1.77 | 53 (24,71) |
| Received only one dose during pregnancy | |||||||||
| First dose during the first trimester | 0 | 0.00 | no estimate | 0 | 0.00 | no estimate | 0 | 0.00 | no estimate |
| First dose during the second trimester | 0 | 0.00 | no estimate | 0 | 0.00 | no estimate | 1 | 9.30 | −58 (−94, 64) |
| First dose during the third trimester | 0 | 0.00 | no estimate | 0 | 0.00 | no estimate | 3 | 1.06 | 74 (19, 92) |
| Omicron period | |||||||||
| Unvaccinated during pregnancy | 54 | 16.98 | Reference | 140 | 18.32 | Reference | 302 | 21.11 | Reference |
| Received ≥2 doses during pregnancy | |||||||||
| Second dose during the first trimester | 26 | 15.67 | 25 (−19,55) | 58 | 13.18 | 24 (−5,45) | 86 | 12.23 | 20 (−2, 38) |
| Second dose during the second trimester | 12 | 11.26 | 36 (−18, 67) | 72 | 19.74 | 6 (−21, 30) | 152 | 19.16 | 4 (−16, 22) |
| Second dose during the third trimester | 16 | 27.22 | −8 (−48, 38) | 45 | 21.50 | 12 (−19, 37) | 82 | 17.75 | 18 (−4, 36) |
| Received only one dose during pregnancy | |||||||||
| First dose during the first trimester | 0 | 0.00 | no estimate | 0 | 0.00 | no estimate | 1 | 6.16 | 66 (−57, 95) |
| First dose during the second trimester | 0 | 0.00 | no estimate | 0 | 0.00 | no estimate | 3 | 35.14 | −44 (−82, 43) |
| First dose during the third trimester | 1 | 16.41 | 3 (−86, 87) | 8 | 26.32 | 19 (−39, 60) | 19 | 24.86 | 6 (−33, 40) |
Calendar day was used as the underlying scale to ensure that infants of vaccinated and unvaccinated mothers are compared on the same calendar days.
VE vaccine effectiveness.
aRate per 100 person-years.
bAdjusted for mother’s age, race/ethnicity, neighborhood deprivation index quartile, insurance payor, KPNC facility, pre-pregnancy BMI, diabetes, hypertension, parity, and child age.