Summer subvariants vaccine evaders?
Will Kennedy's ACIP evade vaccines?
COVID infections low as summer starts Along with low virus levels in wastewater, the national rate of positive clinical tests has held steady below 3% for 5 weeks (CDC). Deaths have dropped under 200/week also.
Measles cases at 1215 are just 60 short of being the highest since the US gained elimination status in 2000 (CDC). Utah became the 36th state with its first case, but more are expected because the reported case was not infected out-of-state (Salt Lake Tribune).
The West Texas outbreak count is 750 with only 3 counties with active transmissions now (TX DSHS). There are 32 additional cases elsewhere in the state.
With summer camps and their close-quarter activities and accommodations having started, CDC is encouraging camps to obtain documentation on the immunity and vaccination status of campers and staff to ensure everyone’s safety. In addition, CDC would like to see that camps have masks and isolation facilities available for infected participants.
Vaccines
Early in June, the NB.1.8.1 subvariant was challenging LP.8.1 to cause the most infections as captured by clinical testing in the US. The latest data showed NB.1.8.1 almost even with LP.8.1, 37% to 39% (CDC). NB.1.8.1 and another JN.1 spinoff, XFG, also began showing up in wastewater and in the testing of international passengers arriving at US airports. Although the airport surveillance showing 33% XFG and 28% NB.1.8.1 compared to 15% LP.8.1 is consistent with the first two causing pre-summer surges abroad, they are likely undercounts because the program is voluntary (CDC’s Traveler-based Genomic Surveillance).
We’re now just two days before the newly reconstituted ACIP meets to consider what to do with COVID vaccines for the fall and winter. However, the draft agenda as of 2:30 a.m. ET Monday only has a vote on recommendations for the RSV vaccine for moms and kids on Wednesday and for Thursday, votes on the flu vaccines, including on the preservative, thimerosal (CDC).
So while Kennedy et al. get their act together and although summer has arrived without a COVID surge yet, let’s look at the viruses causing surges abroad and see if our current vaccines will work to mitigate a surge here.
• Nimbus and Stratus are the meteorological names given to NB.1.8.1 and XFG, respectively. The first has been in the news as causing razor-blade sore throats for a more unpleasant symptom than usual, but both have not been reported to cause more severe disease than past variants.
These viruses are each hybrids of different pairs of JN.1 offshoots and have had about a 75% growth advantage over LP.8.1 in spreading globally from April 2024 to April this year (Global Initiative on Sharing All Influenza Data – also does COVID). Nimbus came out of China and has started surges worldwide. Stratus is a Canadian export accounting for 25% of infections in Europe a month ago (Gavi, the Vaccine Alliance).
• Some evasion of neutralizing antibodies Moderna’s current vaccine can produce antibodies against NB.1.8.1 in mice (https://covidandvaccineupdate.substack.com/p/lp81-fall-booster). In a new study with people who had COVID infections by JN.1 and could have antibodies for JN.1 lineage viruses, such as NB.1.8.1 and XFG, these antibodies were ~40% less effective than in the neutralization of LP.8.1.1. The lower effectiveness was due to the additional mutations in the cell-receptor-binding domain of the newer viruses (Table 2 derived from data in Guo et al., Lancet [2025]).
The NB.1.8.1 mutations that inhibited antibody binding left binding to the ACE2 receptor on cells substantially intact. However, this was not the case with XFG, which did not infect cells efficiently (Guo et al.). Thus, of the two viruses, it’s NB.1.8.1 with both the ability to resist antibodies and to infect cells that could start the summer surge here.
The next report will be on the ACIP meeting.
© 2025 Henry A. Choy. All rights reserved.