Strain Intelligence
Circulating Strains · VE by Strain · Antigenic Match
Traditional vaccines depend on strain match. When the circulating virus drifts, VE collapses. Investigational Prophylactic targets neuraminidase across strains — pan-strain by design.
Why strain matters for Investigational Prophylactic
Season 2025–26 saw 92.7% A(H3N2) subclade K prevalence [PMID:42307948] — a new antigenic subclade with poor VE match. Investigational Prophylactic's Long-acting flu prophylactic inhibits neuraminidase directly and is designed to hold efficacy across strains, subtypes, and clades.
H3N2 subclade K, 2025-26
92.7%
Antigenic drift
Mismatched seasons since 2016
4 of 10
Antigenic drift or subclade
VE vs H3N2 (adults)
22%
95% CI 12–31
Investigational Prophylactic target VE
76%
Pan-strain, flat by design
Strain Circulation — 10 Seasons
Share of positive tests by strain (H1N1, H3N2, B/Yamagata, B/Victoria)
B/Yamagata has not co-circulated since 2020 — quadrivalent may become trivalent by 2026-27.
VE by Strain — Adults + High-Risk Subgroups
Point estimates with 95% CIs across the four flu targets
H3N2 mismatch drags overall VE. Note IC bar sits below 10% for every strain.
Antigenic Match × VE — Season Heatmap
Green = match; red = drift. Cell value = VE % that season.
| 2016-17 | 2017-18 | 2018-19 | 2019-20 | 2020-21 | 2021-22 | 2022-23 | 2023-24 | 2024-25 | 2025-26 | |
|---|---|---|---|---|---|---|---|---|---|---|
| A(H3N2) | 12% drift | 8% drift | 45% match | 40% match | — not circ. | 4% drift | 48% match | 42% match | 50% match | 14% drift |
| A(H1N1)pdm09 | 65% match | 42% match | 44% match | 40% match | — not circ. | — not circ. | 52% match | 55% match | 58% match | 55% match |
| B/Yamagata | 55% match | 28% drift | — not circ. | — not circ. | — not circ. | — not circ. | — not circ. | — not circ. | — not circ. | — not circ. |
| B/Victoria | — not circ. | 40% match | 60% match | 22% drift | — not circ. | 48% match | 45% match | 52% match | 44% match | 48% match |
Legend match, VE ≥50% match, 30–49% match, <30% antigenic drift not circulating
Match/mismatch classification from CDC surveillance. Mismatch years directly correlate with hospitalization spikes.