TABLE 4.
Prevalence of anti-H3 influenza virus antibodies in healthy humans
| Assay | Age group | Total no. of sera | Titer | No. of sera (%) |
||||
|---|---|---|---|---|---|---|---|---|
| HK1/68 | Dar6/21d | Ck/481 | Ck/8520 | Ck/6673 | ||||
| HI (n = 498)a | <18 | 1 | Neg.c | 1 | 0 | 1 | 1 | 1 |
| ≥40 | 0 | 1 | 0 | 0 | 0 | |||
| 18−49 | 349 | Neg. | 286 | 201 | 345 | 343 | 347 | |
| ≥40 | 63 (18%) | 148 (42%) | 4 (1%) | 6 (2%) | 2 (1%) | |||
| ≥50 | 148 | Neg. | 18 | 77 | 129 | 126 | 136 | |
| ≥40 | 130 (87%) | 71 (48%) | 19 (13%) | 22 (15%) | 12 (8%) | |||
| All age group | 498 | Neg. | 305 | 278 | 475 | 470 | 484 | |
| ≥40 | 193 (39%) | 220 (44%) | 23 (5%) | 28 (6%) | 14 (3%) | |||
| MN (n = 129)b | 18−49 | 54 | Neg. | 42 | 53 | 54 | 54 | 54 |
| ≥40 | 12 (22%) | 1 (2%) | 0 | 0 | 0 | |||
| ≥50 | 75 | Neg. | 5 | 73 | 73 | 70 | 73 | |
| ≥40 | 70 (93%) | 2 (3%) | 2 (3%) | 5 (7%) | 2 (3%) | |||
| All age group | 129 | Neg. | 47 | 126 | 127 | 124 | 127 | |
| ≥40 | 82 (64%) | 3 (2%) | 2 (2%) | 5 (4%) | 2 (2%) | |||
a
HI, hemagglutination inhibition assay.
b
Sera had a hemagglutination inhibition (HI) titer ≥10 against H3N8 viruses subjected to microneutralization (MN) test (n = 129).
c
Negative, HI, or MN titers <40.
d
Dar6/21 or Darwin/6/2021.