Background

In the United States, EG.5.1 has become the most prevalent COVID-19 variant, making up 17.3% of cases for the two-week period ending Aug. 5. The most common variants after EG.5.1 are XBB.1.16 (15.6%), XBB.2.23 (11.2%), and XBB.1.5 (10.3%).

The World Health Organization (WHO) has designated EG.5.1 as a "variant of interest," but said it doesn't seem to pose more of a public health threat than other variants.

"Based on the available evidence, the public health risk posed by EG.5 is evaluated as low at the global level, aligning with the risk associated with XBB.1.16 and the other currently circulating VOIs," WHO said in a risk evaluation published earlier this month. "While EG.5 has shown increased prevalence, growth advantage, and immune escape properties, there have been no reported changes in disease severity to date."

Meanwhile, FL.1.5.1 has also started to surge in the United States, especially in the Northeast, where it accounts for one-fifth of estimated cases. According to CDC, the variant accounted for 8.6% of all cases nationwide as of earlier this month.

Drugmakers announce updated vaccines are effective against new variants

Both Moderna and Pfizer, as well as other drugmakers like Novavax, have created updated versions of their COVID-19 vaccines aimed at the XBB.1.5 variant. Both EG.5.1 and FL.1.5.1 descend from the XBB subvariant.

WHO specifically noted the strain that EG.5.1 descends from has the "same spike amino acid profile as XBB.1.5," which is what mRNA COVID-19 vaccines target.

On Thursday, Moderna said initial study data shows its updated COVID-19 vaccine is effective against both the EG.5.1 and FL.1.5.1 variants.

In a statement, Moderna said "preliminary clinical trial data confirm its updated COVID-19 vaccine for the fall 2023 vaccination season showed a significant boost in neutralizing antibodies against EG.5 and FL.1.5.1 variants."

"These results suggest that Moderna's updated COVID-19 vaccine may effectively target the expected circulating variants of COVID-19 during the upcoming vaccination season," the company added.

Meanwhile, Pfizer announced Thursday that its updated COVID-19 shot showed neutralizing activity against the EG.5 variant in a study conducted on mice. (Jain, Reuters, 8/17 [1]; Choi, The Hill, 8/17; Constantino, CNBC, 8/17; Jain, Reuters, 8/17 [2]; Tétrault-Farber/Leo, Reuters, 8/9)