Table 3.
Estimated Vaccine Effectiveness of a Messenger RNA (mRNA) Booster Dose Against Coronavirus Disease 2019 Among US Healthcare Personnel who Received 2 mRNA Doses, October 2021–June 2022
| Characteristic by Variant Period | Booster Dose Recipients/Recipients of 2 Doses ≥5 mo Earlier (%)a | Adjusted VE (95% CI)b | |
|---|---|---|---|
| Case-Participants | Control-Participants | ||
| Overall period | |||
| Booster product | |||
| Any mRNA | 1854/3190 (58.1) | 3153/3892 (81.0) | 71.1 (66.7–75.0) |
| Pfizer BioNTech | 1373/2301 (59.7) | 2327/2808 (82.9) | 71.2 (65.8–75.7) |
| Moderna | 391/790 (49.5) | 693/948 (73.1) | 71.6 (61.3–79.2) |
| Time since booster, d | |||
| <60 | 356/1692 (21.0) | 817/1556 (52.5) | 78.2 (73.6–82.0) |
| 60–119 | 982/2318 (42.4) | 1505/2244 (67.1) | 67.1 (60.9–72.3) |
| ≥120 | 516/1852 (27.9) | 831/1570 (52.9) | 33.6 (6.6–52.8) |
| Delta periodc | |||
| Booster product | |||
| Any mRNA | 96/613 (15.7) | 422/815 (51.8) | 86.3 (81.1–90.1) |
| Pfizer BioNTech | 76/416 (18.3) | 335/580 (57.8) | 88.0 (82.3–91.9) |
| Moderna | 17/193 (8.8) | 73/220 (33.2) | 85.4 (69.4–93.0) |
| Time since booster, d | |||
| <60 | 68/585 (11.6) | 331/724 (45.7) | 86.2 (80.4–90.3) |
| 60–119 | 28/545 (5.1) | 91/484 (18.8) | 86.6 (74.8–92.9) |
| ≥120 | 0/517 (0) | 0/393 (0) | … |
| Omicron periodc | |||
| Booster product | |||
| Any mRNA | 1758/2577 (68.2) | 2731/3077 (88.8) | 64.6 (58.4–69.9) |
| Pfizer BioNTech | 1297/1885 (68.8) | 1992/2228 (89.4) | 63.6 (55.8–69.9) |
| Moderna | 374/597 (62.6) | 620/728 (85.2) | 66.8 (53.0–76.6) |
| Time since booster, d | |||
| <60 | 288/1107 (26.0) | 486/832 (58.4) | 73.4 (66.6–78.9) |
| 60–119 | 954/1773 (53.8) | 1414/1760 (80.3) | 63.8 (56.6–69.8) |
| ≥120 | 516/1335 (38.7) | 831/1177 (70.6) | 32.1 (4.5–51.7) |
Abbreviations: CI, confidence interval; mRNA, messenger RNA; VE, vaccine effectiveness.
Case-participants had symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection confirmed by antigen test or nucleic acid amplification test (NAAT); control-participants had a negative SARS-CoV-2 NAAT result, with or without symptoms. Vaccination status was assigned on the test date as after a booster dose if ≥14 days after an mRNA booster dose administered ≥5 months after dose 2; the referent group was participants with dose 2 receipt ≥5 months before the test date without a booster dose.
VE was estimated as 100% multiplied by (1 minus the odds ratio for vaccination status) by case/control status. A conditional model was used with a cluster of 2-week matching period and enrolling site to account for matching. Adjusted VE included age group in years (18–29, 30–39, 40–49, or ≥50 years), race and ethnicity (white non-Hispanic or other), educational level (doctoral/professional degree or other), underlying health conditions (yes or no), known contact with a person with coronavirus disease 2019 outside the workplace (yes or no).
The Delta-predominant period was defined as before 19 December 2021; the Omicron-predominant period, as 19 December 2021 or later.