Table 2.
Estimated effectiveness ≥ 14 days after 2nd mRNA COVID-19 vaccination against new detection of SARS-CoV-2 anti-nucleocapsid antibody, March–October 2021.
| Characteristic | Case-participantsa | Control-participantsa |
VE (95% CI) Unadjustedb |
Case-participantsa | Control-participantsa |
VE (95% CI) Adjustedb |
|---|---|---|---|---|---|---|
| By vaccine product | ||||||
| Any mRNA | 154 | 1540 | 91.0 (85.0–94.6) | 154 | 1512 | 88.8 (79.6–93.9) |
| Pfizer-BioNTech | 131 | 1000 | 89.0 (81.0–93.6) | 131 | 982 | 87.8 (75.9–93.8) |
| Moderna | 63 | 605 | 95.9 (89.4–98.4) | 63 | 595 | 91.7 (75.7–97.2) |
| By calendar periodc | ||||||
| Pre-Delta | 52 | 552 | 93.0 (84.9–96.8) | 52 | 541 | 93.2 (80.9–97.5) |
| Delta | 102 | 988 | 92.5 (83.7–96.5) | 102 | 971 | 89.0 (72.0–95.6) |
| By time since dose 2 | ||||||
| <3 months | 75 | 686 | 92.5 (85.1–96.2) | 75 | 675 | 93.5 (83.8–97.4) |
| ≥3 months | 119 | 919 | 88.0 (75.5–94.2) | 119 | 902 | 81.6 (56.6–92.2) |
| By age group (years) | ||||||
| 18–49 | 74 | 483 | 93.6 (83.1–97.6) | 74 | 471 | 95.2 (83.9–98.6) |
| ≥50 | 80 | 1057 | 81.0 (55.7–91.8) | 80 | 1041 | 75.9 (36.3–90.9) |
| By underlying health conditiond | ||||||
| 0 | 39 | 358 | 92.6 (65.3–98.4) | 39 | 352 | 93.9 (45.1–99.3) |
| 1 | 40 | 412 | 84.4 (49.2–95.2) | 40 | 403 | 89.7 (36.3–98.3) |
| >1 | 75 | 767 | 85.0 (63.8–93.8) | 75 | 757 | 85.9 (52.2–95.9) |
a. Case-participants had new serologic evidence of SARS-CoV-2 infection, defined as a positive anti-nucleocapsid antibody following a negative serology test result; control-participant had serologic evidence of no infection, indicated by a negative anti-spike antibody, or negative anti-nucleocapsid antibody.
b. Vaccine effectiveness (VE) was estimated as 100- (100 × odds ratio) with the unvaccinated group as the referent. Conditional logistic regression models accounted for matching by calendar time and adjusted for region of enrollment site, age, healthcare worker occupation, population density of county of residence, and recent close contact with COVID-19.
c. Pre-Delta period defined as March 1, 2021–June 30, 2021; Delta period defined as July 1, 2021–October 31, 2021.
d. Defined using self-report and electronic health record information as autoimmune disease, cardiovascular disease, diabetes, immunocompromised state, liver disease, obesity, pulmonary disease, renal disease, substance abuse, mental health conditions, neurologic disease, sickle cell disease.