With the LP.8.1.* variant on the way to dominance in most places, it is time to ponder which variant might drive the next wave.
The leading contenders at this point are LF.7.7.2, LF.7.9, NB.1.8.1, XEC.25.1 and XFH.
I show them here using a log scale, so you can compare their growth rates vs the most common LP.8.1.* sub-lineage: LP.8.1.1.
LF.7.7.2 is descended from FLiRT JN.1.16.1. LF.7 added several Spike mutations: T22N, S31P, K182R, R190S and K444. Then LF.7.7.2 added the Spike H445P mutation.
LF.7.7.2 has been most successful in Canada (especially Quebec), rising to 12% frequency. The US has reported growth to 4%.
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NB.1.8.1 is descended from XDV.1.5.1. XDV was a recombinant of XDE and JN.1. XDE was a recombinant of GW.5.1 and FL.13.4, so this represents the last current variant with any non-JN.1 ancestry.
XDV.1 added the F456L mutation, then XDV.1.5 added G184S and K478I. NB.1 then added Spike mutations: T22N and F59S. Then NB.1.8 added the Spike Q493E mutation that characterised KP.3.1 FLuQE – an example of convergent evolution. Finally NB.1.8.1 added the A435S mutation.
NB.1.8.1 has mainly been reported from Hong Kong, rising to 50% frequency.
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LF.7.9 is descended from FLiRT JN.1.16.1. LF.7 added several Spike mutations: T22N, S31P, K182R, R190S and K444. Then LF.7.9 added the Spike L441R, H445P and A475V mutations.
LF.7.9 has been most successful in Ireland, rising to 50% frequency. The UK and France have reported growth to 5%.
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XEC.25.1 adds the A435S mutation.
XEC.25.1 has only been reported from Singapore, rising to 40% frequency. Prior to this sub-lineage, the XEC.* variant had not been dominant in Singapore.
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XFH is a recombinant of LF.7.1 and XEF. XEF was a recombinant of LB.1.4 and KP.3.
XFH has been most successful in Singapore, rising to 7% frequency. The UK has reported growth to 6%.
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So in summary, the most obvious contender to challenge LP.8.1.1 at this point looks like LF.7.7.2, considering it’s healthy growth rate and sustained success in North America. But all of the contenders seem limited to particular countries or regions so far.
I will continue to monitor this topic.
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The usual caveats apply - recent sample sizes are smaller which might skew these results, and “global” sequencing data is dominated by wealthy countries, with many under-sampled regions.
Honourable mention to NB.1.8 (low growth so far).
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Mike,
I understand that FDA did bypass the APIC and VRBPAC process, worked with the WHO and designated flu strains for the fall vaccines.
Domyou know if they did the same for COVID? I have seen nothing on that.
I also have seen nothing about whether FDA will allow mRNA vaccines, or whether the political stupidity will prevent those.
Do you know?
FDA did designate the flu strains for the 2025/2026 season:
egg-based influenza vaccines:
an A/Victoria/4897/2022 (H1N1)pdm09-like virus;
an A/Croatia/10136RV/2023 (H3N2)-like virus; and
a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
cell- or recombinant-based flu vaccines
an A/Wisconsin/67/2022 (H1N1)pdm09-like virus;
an A/District of Columbia/27/2023 (H3N2)-like virus; and
a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
Today, the FDA made recommendations to vaccine manufacturers for the virus strains to be used in the trivalent (three strain) flu vaccines for the 2025-2026 U.S. flu season following a thorough and comprehensive review of U.S. and global surveillance data.
The #WHO Covid vaccine composition for 2025-2026 will be set in May.
The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) continues to closely monitor the genetic and antigenic evolution of SARS-CoV-2 variants, immune responses to SARS-CoV-2 infection and COVID-19 vaccination, and the performance of COVID-19 vaccines against circulating variants. Based on these evaluations, WHO advises vaccine manufacturers and regulatory authorities on the implications for future updates to COVID-19 vaccine antigen composition.
Mike Honey
Sam