TABLE 3.
Estimation of relative morbidity due to influenza A (H3N2) viruses from 1993 to 1997 in Japan
| Epidemic seasona | No. of ILIsb | No. of influenza virus isolatesc
|
Relative morbidity due to H3N2 influenza virusd | |||
|---|---|---|---|---|---|---|
| A/H1N1 | A/H3N2 | B | Total | |||
| 1993 (10/92–10/93) | 877,520 | 0 | 1,278 | 2,403 | 3,681 | 304,665 |
| 1994 (10/93–10/94) | 76,461 | 0 | 457 | 79 | 536 | 65,192 |
| 1995 (10/94–10/95) | 735,175 | 88 | 1,917 | 1,890 | 3,895 | 361,831 |
| 1996 (10/95–10/96) | 176,260 | 3,475 | 237 | 3 | 3,715 | 11,245 |
| 1997 (10/96–10/97) | 317,305 | 0 | 3,217 | 1,231 | 4,448 | 229,490 |
a
The epidemic season in Japan begins in October and continues until October of the next year, as indicated in parenthesis.
b
Numbers of ILIs represent the number of influenza-like illnesses reported by elementary, junior high, and high schools to the Ministry of Health and Welfare, Tokyo, Japan.
c
Influenza virus isolates represent the numbers of viruses isolated by prefectural and municipal institutes of hygiene as reported to the National Institute of Infectious Diseases, Tokyo, Japan.
d
Relative morbidity due to H3N2 influenza virus was determined as follows: relative morbidity = ILI × (number of H3N2 isolates/total number of isolates).