Volume 30, Number 11—November 2024
Research
Antiviral Susceptibility of Swine-Origin Influenza A Viruses Isolated from Humans, United States
Table 2
Baloxavir susceptibility of variant influenza viruses in cell culture-based IRINA in study of antiviral susceptibility of swine-origin influenza A viruses isolated from humans, United States*
| Influenza viruses | Amino acid change in PA-CEN† | Mean EC50 + SD, nM (fold change) |
|---|---|---|
| A(H1N1v) median EC50, n = 15 | 0.75 | |
| A/Iowa/33/2017 clone 1‡ | – | 1.33 + 0.07 (2; 1) |
| A/Iowa/33/2017 clone 2‡ |
I38M |
19.98 + 2.17 (27; 15) |
| A(H1N2v) median EC50, n = 14 |
– |
0.98 |
| A(H3N2v) median EC50, n = 21 | 1.27 | |
| A/Michigan/84/2016 | – | 1.53 + 0.31 (1; 1) |
| A/New Jersey/53/2015 |
E199G |
1.50 + 0.17 (1; 1) |
| Reference seasonal viruses¶ | ||
| A/Louisiana/50/2017(H3N2) | – | 1.08 + 0.17 (NA; 1) |
| A/Louisiana/49/2017(H3N2) | I38M | 14.06 + 2.96 (13) |
*Each virus was tested in >3 independent experiments to determine EC50 value. Fold-change: EC50 of variant virus containing PA amino acid substitution relative to subtype-specific median or the wild-type PA sequence-matched virus, respectively. Variant viruses lacking PA markers were used to determine the median EC50s (Appendix Table 3, https://wwwnc.cdc.gov/EID/article/30/11/24-0892-App1.pdf). Dashes indicate the absence of known or suspected molecular markers for reduced baloxavir susceptibility. EC50, 50% effective concentration; IRINA, influenza replication inhibition neuraminidase-based assay; NA, not applicable; PA, polymerase acidic; PA-CEN, PA cap-dependent endonuclease;. †PA-CEN domain encompasses the N-terminal amino acid residues 1 to 209 in PA protein. ‡These viruses were previously tested (40). ¶Source: Centers for Disease Control and Prevention Baloxavir Susceptibility Reference Virus Panel (IRR: FR-1678 ver1.1) (https://www.isirv.org/site/index.php/reference-panel).
1These authors contributed equally to this article.