Table 3.
Virus and patient characteristics for type A and B influenza viruses (n = 53) containing PA amino acid substitutions of concern and phenotypically tested by WHO CCs for baloxavir susceptibility.a
| Virus (n) | n | EC50 fold-change as compared to reference median EC50 values | PA substitutionb | Patient setting | Antiviral treatment | Immunocompromised | |
|---|---|---|---|---|---|---|---|
| Virus isolate | Clinical specimen | ||||||
| A(H1N1)pdm09 (14 of 984) | 2 | 11.4–32.2 | I38T | I38T/I mix | Community | Yes, baloxavir | No |
| 1 | 12.4 | I38 T/F mix | I38T/F/I mix | Community | Yes, baloxavir | No | |
| 2 | 36.9–49.5 | I38S | I38S | Community | Yes, baloxavir | No | |
| 3 | 3.0–3.7 | I38V | I38V | Community | Yes, laninamivir | No | |
| 1 | 2.5 | I38F/I mix | I38F/I mix | Unknown | Unknown | Unknown | |
| 1 | 6.9 | E23G | E23G | Unknown | Unknown | Unknown | |
| 1 | 7.4 | E23K | E23K | Community | No | No | |
| 2 | 1.6–4.7 | K34R | K34R | Unknown | Unknown | Unknown | |
| 1 | 2.9 | E199G | E199G | Unknown | Unknown | Unknown | |
| A(H3N2) (37 of 768) | 21 | 64.3–614.0 | I38T | I38T (10) I38T/I mix (9) I38T/K/I mix (1) Not availablec (1) |
Community (19) Hospital (2) |
Yes, baloxavir (17) Yes, oseltamivir (1) No (3) |
No (20) Unknown (1) |
| 7 | 5.6–250.0 | I38T/I mix | I38T/I mix | Community | Yes, baloxavir | No | |
| 1 | 25.6 | I38 T/M/I mix | I38T/M/I mix | Community | Yes, baloxavir | No | |
| 1 | 23.7 | I38M | I38M | Community | Yes, baloxavir | No | |
| 2 | 1.0–91.8 | I38M/I mix | I38M/I mix (1) I38 (1) | Community (1) Unknown (1) | Yes, baloxavir (1) Unknown (1) |
No (1) Unknown (1) |
|
| 1 | 4.1 | I38L | I38L | Unknown | Unknown | Unknown | |
| 1 | 4.1 | K34R | K34R | Unknown | Unknown | Unknown | |
| 2 | 0.5–1.3 | L28P | L28P (1) Not available (1) |
Unknown | Unknown | Unknown | |
| 1 | 0.9 | I38V/I mix | Not available | Unknown | Unknown | Unknown | |
| B/Victoria (2 of 425) | 1 | 0.9 | I38V | I38V | Unknown | Unknown | Unknown |
| 1 | 0.6 | M34I | Not available | Unknown | Unknown | Unknown | |
The number of viruses for which data were reported is shown in parentheses if the number is less than the number in the ‘n’ column.
PA amino acid substitutions associated with reduced susceptibility to baloxavir, as listed in the summary table provided by the AVWG on the WHO website (https://cdn.who.int/media/docs/default-source/influenza/summary-of-polymerase-acidic-(pa)-protein-amino-acid-substitutions-analysed-for-their-effects-on-baloxavir-susceptibility.pdf?sfvrsn=442806e_1&download=true) are shown. Substitutions at PA residue 34 are included.
Clinical specimen not available for testing.