Disease experts anticipate an uptick in Covid cases this summer as a new variant spreads.
The KP.2 variant accounts for 28% of Covid infections in the US, up from just 6% in mid-April, according to data released Friday by the Centers for Disease Control and Prevention.
KP.2 became dominant in late April – meaning it is responsible for the majority of new cases – overtaking the JN.1 variant, which took over in the winter.
Some scientists collectively refer to KP.2 and another variant called KP.1.1, which shares the same key mutations, as “FLiRT” – a reference to their amino acid changes.
Both are descendants of JN.1, which is part of the omicron lineage, like all versions of the coronavirus that have gained dominance in recent years.
But KP.2 has three additional mutations in its spike protein compared to JN.1, which disease experts say could make it easier for the virus to evade protection from vaccines or previous infections.
“It appears that these additional mutations make the immune system more evasive, so it’s not a surprise that it dominates,” said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston.
Laboratory research from Japan, which was published as a preprint and has not been peer-reviewed, suggests that the Covid vaccines currently recommended in the US may be less effective against KP.2 than against JN.1.
However, KP.2 may be less efficient at infecting cells, the research suggests, which could mean that a higher dose of the virus would be needed to infect someone.
People infected with JN.1 should still have some protection against KP.2, experts said.
The CDC doesn’t collect regular data on how Covid symptoms evolve over time, so it’s difficult to assess whether illnesses caused by KP.2 look different. Covid symptoms have been generally consistent over the past two years or so.
Experts predict a small increase in cases this summer
Covid cases have increased every summer in the US since 2020. If KP.2 continues to gain prevalence, this pattern could repeat itself – but not as dramatically, experts predict.
The US is in a good position with Covid heading into the summer, according to Andrew Pekosz, a virologist at Johns Hopkins University. Hospitalizations hit record lows in late April, the last data available before the CDC stopped requiring hospitals to report Covid hospitalization numbers.
“We see a spike in cases in late summer and early fall, and then we see a second spike in cases around the Christmas, New Year’s holiday,” Pekosz said. “This pattern has been repeating itself for a few years. The important thing, however, is that the magnitude of cases has been consistently decreasing.”
Several factors could help the KP.2 variant spread this summer. When the weather gets too hot, people tend to gather indoors to escape the heat, creating new opportunities for transmission. Many people have also not been vaccinated recently; less than a quarter of U.S. adults received the updated Covid vaccine.
“I think there will be a significantly large susceptible population out there, due to this combination of waning immunity and viral evolution, and we will see a number of cases this summer,” said Dr. Thomas Russo, chief of infectious diseases. diseases at the University at Buffalo Jacobs School of Medicine and Biomedical Sciences.
But he added that as most people have some immunity to Covid, it is possible that “the wave will not be as big” as in previous years.
Barouch said last summer’s surges coincided with the arrival of new variants, so this year could be similar.
“Summer surges have often occurred in the context of new variants, like the original Delta wave, for example, or the BA.5 wave,” he said. “So I wouldn’t be surprised if there was another surge in the summer.”
Will KP.2 affect vaccine recommendations?
The rise of KP.2 raises questions for public health experts deciding which variants will be targeted by new Covid vaccines.
The Food and Drug Administration on Tuesday postponed an advisory committee meeting the goal was to decide which strains to include in the updated vaccine formula for the fall.
“We have recently observed changes in the dominant circulating strains of SARS-CoV-2,” said an FDA spokesperson. “The additional time will allow the agency to obtain more up-to-date surveillance data and other information about circulating strains of SARS-CoV-2 to better inform the committee’s discussions and recommendations.”
The latest vaccine-related recommendations from the CDC came in February, when he suggested that people aged 65 and over should receive an additional dose and that younger people could consider one.
People who have not received the updated vaccine and feel they need it “should get the vaccine that is currently available,” Barouch said.
But Pekosz said people who aren’t immunocompromised could probably wait until the fall.
“With the number of cases relatively low at the moment, I think the prudent thing to do is to try to wait until September and get the new formulation,” he said.
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