Table 2. Rate Ratios of Confirmed SARS-CoV-2 Infection According to Age Group and Vaccination Period.*.
| Age Group | Vaccination Period | ||||||
|---|---|---|---|---|---|---|---|
| Jan. 16–31 | Feb. 1–15 | Feb. 16–28 | March 1–15 | March 16–31 | April 1–30 | May 1–31 | |
| 16–39 Yr | |||||||
| Rate ratio of reference vs. period (95% CI) | 0.8 (0.7–0.9) | 0.7 (0.7–0.8) | 0.9 (0.8–1.0) | Reference | 1.2 (1.1–1.3) | 1.5 (1.4–1.8) | 1.6 (1.3–2.0) |
| Adjusted rate — no. of events/wk/100,000 persons | 108.7 | 117.9 | 93.4 | 85.7 | 72.7 | 55.4 | 52.1 |
| 40–59 Yr | |||||||
| Rate ratio of reference vs. period (95% CI) | 0.9 (0.8–1.0) | 1.0 (0.9–1.0) | Reference | 1.1 (1.0–1.2) | 1.4 (1.3–1.6) | 1.7 (1.4–2.1) | 2.1 (1.4–3.0) |
| Adjusted rate — no. of events/wk/100,000 persons | 117.2 | 110.7 | 106.0 | 95.9 | 75.0 | 61.3 | 51.2 |
| ≥60 Yr | |||||||
| Rate ratio of reference vs. period (95% CI) | Reference | 1.1 (1.1–1.2) | 1.3 (1.1–1.5) | 1.6 (1.4–2.0) | 1.6 (1.3–2.0) | 2.2 (1.6–3.1) | 2.2 (1.3–3.6) |
| Adjusted rate — no. of events/wk/100,000 persons | 105.7 | 92.4 | 82.3 | 64.3 | 65.2 | 47.9 | 49.1 |
Analyses were adjusted for week of infection, number of previous PCR tests (0, 1, or ≥2), population sector, and sex. Shown are rate ratios for confirmed SARS-CoV-2 infection during the period of July 11 through 31, 2021 (study period), as a function of time since full vaccination. We defined fully vaccinated persons as those for whom 7 days or more had passed since receipt of the second dose of the BNT162b2 vaccine. The comparison was between the estimated rate among persons who became fully vaccinated during the first vaccination period in which their age group was eligible (reference; i.e., January 16 to 31 for persons ≥60 years of age, February 16 to 28 for persons 40 to 59 years of age, and March 1 to 15 for persons 16 to 39 years of age) and the estimated rate among persons who became fully vaccinated in another vaccination period. For example, among persons 60 years of age or older, the rate of confirmed SARS-CoV-2 infection during the July 11–31 period among those vaccinated in January (105.7 events per week per 100,000 persons) was divided by the rate among those vaccinated in the second half of March (65.2 events per week per 100,000), yielding a rate ratio of 1.6. The 95% confidence intervals are not adjusted for multiplicity.