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Table 2 Risk of post-vaccinial encephalitis (P.V.E.) and death from primary smallpox vaccinations, Stratified by age and study, 1963–1968

From: Risks of serious complications and death from smallpox vaccination: A systematic review of the United States experience, 1963–1968

Age group and studies Number vaccinated P.V.E. No. Deaths No. Risk of complication per million (95% C.I.)a Risk of death per million (95% C.I.)a Case fatality risk per hundred (95% C.I.)a
Age <1          
   Neff 1967a 654,000 1 0 1.5 (0.04, 8.5) 0.0 (0.0, 5.6) 0.0 (0.0, 97.5)
   Neff 1967b 31,000 1 0 32.3 (0.8, 180) 0.0 (0.0, 119) 0.0 (0.0, 97.5)
   Lane 1969 614,000 4 3 6.5 (1.8, 167) 4.9 (1.0, 14.3) 75.0 (19.4, 99.4)
   Lane 1970 17,000 3 1 176.5 (36.4, 515) 58.8 (1.5, 328) 33.3 (0.84, 90.6)
   Ratner 1970 1 0 0 n/c n/c n/c n/c n/a n/a
   Neff 1972 32 0 0 n/c n/c n/c n/c n/a n/a
   Summary 1,316,033 9 4 6.8 (3.1, 13.0) 3.0 (0.8, 7.8) 44.4 (13.7, 78.8)
Age 1 to 4          
   Neff 1967a 2,973,000 2 1 0.7 (0.08, 2.4) 0.3 (0.008, 1.9) 50.0 (1.3, 98.7)
   Neff 1967b 142,000 0 0 0.0 (0.0, 26.0) 0.0 (0.0, 26.0) n/a n/a
   Lane 1969 2,733,000 6 0 2.2 (0.8, 4.8) 0.0 (0.0, 1.3) 0.0 (0.0, 45.9)
   Lane 1970 317,000 3 0 9.5 (2.0, 27.6) 0.0 (0.0, 11.6) 0.0 (0.0, 70.8)
   Ratner 1970 68,002 0 0 0.0 (0.0, 54.2) 0.0 (0.0, 54.2) n/a n/a
   Neff 1972 517 0 0 0.0 (0.0, 7110) 0.0 (0.0, 7110) n/a n/a
   Summary 6,233,519 11 1 1.8 (0.9, 3.2) 0.2 (0.004, 0.9) 9.1 (0.23, 41.3)
Age 5 to 19          
   Neff 1967a 2,295,000 8 4 3.5 (1.5, 6.9) 1.7 (0.5, 4.5) 50.0 (15.7, 84.3)
   Neff 1967b 110,000 0 0 0.0 (0.0, 33.5) 0.0 (0.0, 33.5) n/a n/a
   Lane 1969 1,959,000 5 1 2.6 (0.8, 6.0) 0.5 (0.01, 2.8) 20.0 (0.50, 71.6)
   Lane 1970 229,000 2 0 8.7 (1.1, 31.5) 0.0 (0.0, 16.1) 0.0 (0.0, 84.2)
   Ratner 1970b 193,721 1 1 5.2 (0.1, 28.8) 5.2 (0.1, 28.8) 100.0 (2.5, 100)
   Summary 4,786,721 16 6 3.3 (1.9, 5.4) 1.2 (0.5, 2.7) 37.5 (15.2, 64.6)
Age 20 +          
   Neff 1967a 317,000 1 0 3.2 (0.1, 17.6) 0.0 (0.0, 11.6) 0.0 (0.0, 97.5)
   Neff 1967b 15,000 0 0 0.0 (0.0, 246) 0.0 (0.0, 246) n/a n/a
   Lane 1969 288,000 1 0 3.5 (0.1, 19.3) 0.0 (0.0, 12.8) 0.0 (0.0, 97.5)
   Lane 1970 33,000 0 0 0.0 (0.0, 112) 0.0 (0.0, 112) n/a n/a
   Ratner 1970b 107,822 0 0 0.0 (0.0, 34.2) 0.0 (0.0, 34.2) n/a n/a
   Summary 760,822 2 0 2.6 (0.3, 9.5) 0.0 (0.0, 4.8) 0.0 (0.0, 84.2)
All agesc          
   Neff 1967a 6,239,000 12 5 1.9 (0.2, 3.4) 0.8 (0.3, 1.9) 41.7 (15.2, 72.3)
   Neff 1967b 298,000 1 0 3.4 (0.1, 18.7) 0.0 (0.0, 12.2) 0.0 (0.0, 97.5)
   Lane 1969 5,594,000 16 4 2.9 (1.6, 4.6) 0.7 (0.2, 1.8) 25.0 (7.3, 52.4)
   Lane 1970 596,000 8 1 13.4 (5.8, 26.4) 1.7 (0.04, 9.3) 12.5 (0.3, 52.6)
   Mellin 1970 109,000 0 0 0.0 (0.0, 33.8) 0.0 (0.0, 33.8) n/a n/a
   Ratner 1970 369,546 1 1 2.7 (0.07, 15.1) 2.7 (0.1, 15.1) 100.0 (2.5, 100)
   Neff 1972 549 0 0 0.0 (0.0, 6697) 0.0 (0.0, 6697) n/a n/a
   Summary 13,206,095 38 11 2.9 (2.0, 3.9) 0.8 (0.4, 1.5) 28.9 (15.4, 45.9)
  1. n/c = not calculated, n/a = not assessable aRisk and confidence intervals not calculated (n/c) for less that 100 vaccinations. Exact confidence intervals based on the binomial distribution. bThe Ratner study age groups, "Age 5 to 14" and "Age 15+", were counted in the Table age groups "Age 5 to 19" and "Age 20+", respectively. cAll ages group may includes subjects whose age was unknown