Table 4.
Sensitivity Analyses of Acute Ischemic Stroke Among US Medicare Fee-for-Service Beneficiaries, Medicare 2019–2021
| Risk period | Number of events |
Crude IRR (95% CI) |
Age-adjusted IRR (95% CI)a |
|---|---|---|---|
| Restricted the starting time of the study period to January 1, 2020 c | |||
| −7 to −1 d | 789 | 1.90 (1.77–2.05) | 1.93 (1.80–2.08) |
| 0–3 d | 2,173 | 10.2 (9.76–10.7) | 10.4 (9.92–10.9) |
| 4–7 d | 322 | 1.58 (1.42–1.77) | 1.61 (1.44–1.80) |
| 8–14 d | 523 | 1.40 (1.28–1.52) | 1.42 (1.30–1.55) |
| 15–28 d | 735 | 1.05 (0.97–1.13) | 1.07 (0.99–1.15) |
| Baselineb | 17,214 | 1.0 | 1.0 |
| Excluding AIS with I63.8 and I63.9 diagnosis codes d | |||
| −7 to −1 d | 403 | 1.95 (1.76–2.15) | 2.00 (1.81–2.21) |
| 0–3 d | 1,108 | 10.3 (9.63–10.9) | 10.5 (9.89–11.2) |
| 4–7 d | 186 | 1.81 (1.57–2.09) | 1.86 (1.61–2.16) |
| 8–14 d | 299 | 1.61 (1.44–1.81) | 1.66 (1.48–1.86) |
| 15–28 d | 392 | 1.15 (1.04–1.27) | 1.18 (1.07–1.31) |
| Baselineb | 14,863 | 1.0 | 1.0 |
| Deleted Medicare FFS beneficiaries who died before the end of observation period e | |||
| −7 to −1 d | 505 | 2.26 (2.17–2.34) | 2.25 (2.16–2.34) |
| 0–3 d | 1,487 | 11.7 (11.6–11.7) | 11.6 (11.6–11.7) |
| 4–7 d | 204 | 1.61 (1.47–1.75) | 1.61 (1.47–1.75) |
| 8–14 d | 353 | 1.61 (1.51–1.72) | 1.61 (1.50–1.71) |
| 15–28 d | 459 | 1.07 (0.98–1.17) | 1.07 (0.98–1.17) |
| Baselineb | 23,708 | 1.0 | 1.0 |
| Medicare FFS beneficiaries who had pneumococcal vaccination and AIS from January 1, 2019, to February 28, 2021 f | |||
| 0–3 d | 256 | 1.13 (0.99–1.25) | 1.13 (0.99–1.28) |
| 4–7 d | 254 | 1.12 (0.99–1.25) | 1.12 (0.98–1.27) |
| 8–14 d | 447 | 1.13 (1.03–1.23) | 1.13 (1.03–1.23) |
| 15–28 d | 841 | 1.07 (0.99–1.14) | 1.07 (0.99–1.14) |
| Baselineb | 21,853 | 1.0 | 1.0 |
Abbreviations: AIS = acute ischemic stroke; CI = confidence interval; COVID-19 = coronavirus disease 2019; FFS = fee-for-service; IRR = incidence rate ratio.
Adjusted by age at diagnosis of COVID-19 of <65–90 years by 2-year age group.
All time from observation start on January 1, 2019, to 7 days before date of COVID-19 diagnoses and after 28 days of diagnosis of COVID-19.
The starting time of the observation period was January 1, 2020, and ended on February 28, 2021 (n = 21,756).
Excluded AIS cases that had I63.8 and I63.9 ICD-10 diagnosis codes (n = 17,251).
Medicare FFS beneficiaries who died before the end of follow-up were excluded (n = 26,716).
Included Medicare FFS beneficiaries who had pneumococcal vaccination and AIS from January 1, 2019, to February 28, 2021. If the Medicare beneficiaries had more than one pneumococcal vaccination or AIS hospitalizations, the first date was chosen for the analysis. The date of pneumococcal vaccination was the starting time of the study period and ended on February 28, 2021. Standard self-controlled case series was used among stroke survivors (n = 23,651).