Antibodies for circulating XFG variant by Novavax and Moderna vaccines
Signs of surge continuing slide include the rates of positive tests and hospitalizations falling, the former for the 5th week from a high of 11.8% to 6.7% and the latter for the 3rd week from a high of 2.6/100 k population to 1.2/100 k (Figure 1 derived with data from CDC, COVID-NET, and NCHS). However, weekly deaths from COVID have remained at 0.8% of all causes for 3 weeks.
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Sniffles season here as COVID winds down to return likely late in the year. The common cold caused mostly by rhinovirus has no vaccine and has been in progress since August. It’s about to peak and will continue for months into winter (Figure 2A derived with data from National Respiratory and Enteric Virus Surveillance System).
Flu is approaching this month and won’t peak until February (Figure 2B).
Measles continues to add cases with outbreaks in neighboring Arizona and Utah at their border. Fifty-five of AZ’s 59 cases are in the northwest corner (AZ Department of Health Services). In the adjacent southwest corner of UT are 31 of the state’s 45 cases (UT Department of Health and Human Services)
The US now totals 1552 cases in 42 states and DC (Johns Hopkins).
Vaccines
• Novavax vaccine boosts antibodies for XFG Novavax’s strategy to not chase the multiple viruses emerging in the JN.1 family, but to target just the progenitor, has resulted in both the 2024-2025 and 2025-2026 vaccines containing the JN.1 spike protein. So is the shot effective against the recent circulating viruses? Neutralizing antibodies for XFG increased 3.8-fold a month after vaccination with the JN.1 jab (Table 1 derived from data in Novavax manuscript). This boost was comparable to the 4.5-times amplification of JN.1 antibodies.
Along with accounting for most new infections in the US, XFG is surging in the UK this fall with NB.1.8.1, another JN.1 relative that’s also still here (BBC). The JN.1 shot also boosted NB.1.8.1 antibodies 4.9-fold as well as 4.8-fold of antibodies for LP.8.1 (the target for the mRNA vaccines).
The clinical trial with 58 adults 18 years and older was conducted October ’24 to May ’25.
• The two Moderna vaccines also boost antibodies for current viruses Moderna recently announced results from a clinical trial showing its 2025-2026 Spikevax and mNEXSPIKE targeting LP.8.1 increased neutralizing antibodies for LP.8.1 more than 8- and 16-fold, respectively (https://covidandvaccineupdate.substack.com/p/real-world-use-of-updated-boosters). Although data for XFG and NB.1.8.1 were not provided, the company has a recent manuscript describing these results from mice with prior COVID vaccinations to mimic people who have acquired immunity through multiple vaccinations and/or infection.
Spikevax and mNEXSPIKE as a booster increased XFG and NB.1.8.1 antibodies as much as 50- to 200-fold two weeks later, with mNEXSPIKE providing the higher levels (Table 2 derived from data in Moderna manuscript.)
© Henry A. Choy. All rights reserved.