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Table 2 Incident rate ratiosa, with 95% confidence intervals (CIs) for cardiovascular eventsa following pandemic influenza vaccination (pandemrix) among higher risk individuals defined on the basis of medication use

From: Influenza vaccination and risk for cardiovascular events: a nationwide self-controlled case series study

  AMI (n = 5032) Stroke (n = 3129) Pulmonary Embolism (n = 859)
No. of events Person-days at risk IRR (95% CI)b No. of events Person-days at risk IRR (95% CI)b No. of events Person-days at risk IRR (95% CI)b
Baseline perioda 3368 1,635,876 1.00 (ref.) 2061 1,017,036 1.00 (ref.) 564 279,612 1.00 (ref.)
Pre-vaccination interval          
 1–14 days 124 70,686 0.85 (0.70–1.02) 55 43,946 0.66 (0.50–0.87) 30 12,082 1.23 (0.83–1.81)
 On the day of vaccination 3 5049 0.29 (0.09–0.89) 3 3139 0.50 (0.16–1.56) 0 863 No estimates
Post vaccination interval          
 1–14 days 105 70,686 0.72 (0.59–0.88) 64 43,946 0.77 (0.59–0.99) 18 12,082 0.73 (0.45–1.19)
 15–28 days 101 70,686 0.70 (0.57–0.85) 80 43,946 0.96 (0.76–1.22) 22 12,082 0.89 (0.57–1.38)
 29–59 days 277 156,519 0.88 (0.77–1.00) 181 97,309 0.99 (0.84–1.18) 49 26,753 0.86 (0.62–1.20)
 60–90 days 261 156,519 0.87 (0.73–1.04) 171 97,309 0.96 (0.77–1.20) 39 26,753 0.65 (0.42–1.00)
 91–120 days 293 141,470 1.01 (0.85–1.20) 167 94,170 0.96 (0.78–1.19) 49 25,890 0.84 (0.56–1.26)
 121–180 days 500 302,940 0.82 (0.74–0.91) 347 188,340 0.92 (0.82–1.04) 88 51,780 0.81 (0.63–1.04)
  1. AMI acute myocardial infarction, IRR incident rate ratio, CI confidence interval
  2. aThese are results from self-controlled case series analysis using data for first-time AMI (n = 5032), stroke (n = 3129) and pulmonary embolism (n = 859) patients who were vaccinated with Pandemrix. The start of observation period was May 1, 2009 and end of observation period was September 30, 2010 or the day of emigration or death (whichever came first). Person-time of each vaccinated individual was divided into following risk-periods: pre-vaccination interval (1–14 days prior to vaccination) and postvaccination intervals (1–14 days, 15–28 days, 29–59 days, 60–90 days, 91–120 days, 121–180 days following vaccination)
  3. bAll remaining part of the observation period was used for baseline comparison (unexposed person-time)
  4. cAdjusted for calendar period (January–March, April–August, and September–December)