TABLE 2.
Study group characteristicsa
| Characteristic | Group |
|||
|---|---|---|---|---|
| 1 (VAR; n = 8) | 2 (VAC; n = 20) | 3 (VAR-VAC; n = 16) | 4 (VAC-VAC; n = 40) | |
| Mean age in yr (range) | 76 (52-86) | 70 (63-80) | 77 (48-87) | 64 (43-76) |
| Mean no. of infections or vaccinations (range) | 1 | 1 | 4 (2-9) | 3 (2-7) |
| Mean period (yr) after last infection/vaccination (range) | 71 (51-83) | 66 (61-75) | 48 (27-77) | 45 (33-75) |
| % Male subjects | 25 | 50 | 50 | 43 |
a
Subjects were divided into four groups based on their infection history. Group 1 consisted of cases of smallpox (VAR) with no history of smallpox vaccination. Group 2 consisted of case-controls for group 1 and included subjects with 1 smallpox vaccination (VAC) but no history of smallpox infection. Group 3 (VAR-VAC) consisted of cases of smallpox with a history of one or more smallpox vaccinations, and group 4 (VAC-VAC) consisted of case-controls for group 3 with a history of multiple smallpox vaccinations but no history of smallpox infection.