A newly identified Covid-19 variant, PJ.2.1, is spreading across multiple countries after emerging in Canada in May 2026. Researchers have found that the variant may have an increased ability to infect human cells, including those with low levels of the ACE2 receptor. However, early laboratory findings suggest it does not significantly evade antibodies produced by existing Covid-19 vaccines. The findings highlight the need for continued monitoring as the virus evolves.According to a report published in the Journal of Infection, the variant was first detected in Ontario, Canada, on May 2, 2026.It has since spread to several parts of the United States, Europe and Asia. Researchers said wastewater surveillance data showed that PJ.2.1 was the fastest-growing Covid-19 variant in the US at the time of their analysis.In the US, the variant was first identified in a patient in New York City on June 30. Subsequent cases were reported in California, Arizona, New Jersey, Virginia, North Carolina, Missouri, Oklahoma, Colorado and Florida.It has also been detected in Singapore, Australia, New Zealand, Israel, France and Spain. In Spain, researchers found evidence of local transmission chains, with cases reported in Catalunya, the Basque Country and the Community of Madrid.The findings come from a preliminary study examining the spread and biological characteristics of PJ.2.1, alongside other circulating Covid-19 variants. Researchers also assessed how effectively antibodies from people who received an updated Covid-19 vaccine could neutralise the new variant.
What makes PJ.2.1 different
PJ.2.1 is classified as a saltation variant, also known as a shift variant. Unlike regular variants that emerge through the gradual accumulation of a few mutations, saltation variants carry a large number of genetic changes.Researchers said such variants are thought to evolve during persistent infections before re-entering the wider population. Their extensive mutations, particularly in the spike protein, can potentially make them more resistant to antibodies.However, PJ.2.1 showed relatively limited resistance to antibodies produced after vaccination with the LP.8.1-adapted Comirnaty mRNA vaccine.The study found that antibodies from vaccinated individuals were only 1.8 times less effective against PJ.2.1 than against the LP.8.1 variant. This was a smaller reduction than that observed for several other circulating variants.By comparison, antibody neutralisation was 11.5 times lower against BA.3.2.2, 7 times lower against XFG.1.1 and 6.6 times lower against NB.1.8.1.The researchers also noted that an XFG-adapted vaccine approved for the 2026/2027 Covid-19 season boosts antibodies that can effectively neutralise PJ.2.1.
Why researchers are concerned
Despite showing limited antibody evasion, PJ.2.1 demonstrated a potentially important difference in how it interacts with human cells.Laboratory experiments found that its spike protein had an increased ability to bind to the ACE2 receptor, which the virus uses to enter human cells.The researchers used an antibody that blocks ACE2 to measure how effectively different variants interact with the receptor. PJ.2.1 was the least sensitive to this antibody, with an inhibitory concentration 50 (IC50) of 204 ng/ml. This indicated stronger ACE2 binding compared with the other variants tested.The variant also entered kidney cells with relatively low levels of naturally occurring ACE2 more efficiently than the other variants examined.Researchers said this ability could help PJ.2.1 infect a wider range of cells and potentially increase its transmissibility.However, they cautioned that further research is needed to establish whether this altered receptor-binding behaviour affects the severity or presentation of Covid-19.The study also raised questions about possible effects on organs outside the respiratory system, including the brain and gut. These potential effects have not yet been established.
Which other Covid variants are circulating
The researchers also examined BA.3.2.2, LP.8.1, NB.1.8.1 and XFG, along with their newer descendants.They found significant regional differences in the variants circulating across the world.BA.3.2.2 was relatively common across the regions studied between May and June 2026, but its prevalence subsequently declined.Variants descended from NB.1.8.1 were more prominent in Australia and Asia. These included PQ.16.1.1, which showed substantial circulation in Asia.Meanwhile, XFG-derived variants were more widespread in Europe and North America. These included XFG.1.1 and RV.1.3.The study also found differences in the age groups affected. BA.3.2.2 was more frequently detected among children aged 0-9 years. The other variants, including PJ.2.1, were more commonly found among people aged 70 and above.
Researchers call for continued surveillance
The researchers said the findings underline the importance of monitoring new Covid-19 variants, particularly as updated vaccines are designed to target specific circulating strains.Although the current findings suggest that PJ.2.1 does not have a major advantage in evading vaccine-induced antibodies, its increased ACE2-binding ability could help explain its rapid spread.They warned that further mutations could also change its behaviour.“However, continued surveillance is required to determine whether PJ.2.1 subvariants emerge with increased antibody evasion,” the researchers said.They added that further studies are needed to understand whether the variant’s altered interaction with human cells could affect disease presentation.
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