A highly infectious, new COVID variant is spreading fast, barely three months after the World Health Organization declared that COVID-19 was no longer a global health emergency.
EG.5, a descendant of a previous XBB strain of Omicron, was first spotted in Indonesia on February 17 and has been spreading steadily since. Infections began surging in mid-June—when a record-breaking number of summer travelers took to the skies and unprecedented high temperatures around the Northern Hemisphere forced people to gather indoors, enabling the virus to spread easily. That alarmed the WHO and led them to elevate EG.5 to a "variant of interest" on August 9, alongside other highly contagious Omicron variants such as XBB.1.5 and XBB.1.16.
"Based on the experience that we have from the previous waves, we can project EG.5 is definitely a big deal," says Rajendram Rajnarayanan, a computational biologist at the New York Institute of Technology campus in Jonesboro, Arkansas.
In the United States, EG.5 is now the most prevalent strain of SARS-CoV-2 and has replaced other XBB variants (XBB.1.5, XBB.1.16, XBB.1.9), according to data from the Centers for Disease Control and Prevention (CDC). This variant is now causing more than 17 percent of all reported COVID-19 cases in the country. The number of hospitalizations has risen by 12.5 percent in the past week to roughly 9,000 cases.
EG.5 is also causing upticks in COVID-19 cases worldwide. The number of new COVID cases between July 10 to August 6—nearly 1.5 million—is 80 percent higher compared to the previous 28 days. EG.5 has also been spotted in at least 51 other countries including in those with high vaccination rates: Canada, Japan, South Korea, and China.
"We should take all of these subvariants very seriously," says Angela Rasmussen, a virologist at Vaccine and Infectious Disease Organization in Saskatoon, Canada.
Using testing kits, when symptoms suggest it could be COVID-19, and masking up and staying home if COVID positive, can slow the spread of the new variant, says Rajnarayanan. “We need to minimize the spread of the virus as much as we can."
A more contagious variant
EG.5 is an offshoot of the XBB branch of the Omicron variant, which first arrived in the Fall of 2022. XBB viruses are the fastest-spreading SARS-CoV-2 variants with the power to overcome immunity gained from vaccination or breakthrough infections of prior Omicron subvariants.
EG.5 differs from its XBB parent by a single change within its spike protein, which protrudes from the surface of the virus. When the spike binds to the ACE2 protein receptors on human cells the virus is able to enter the human nasal passage and lungs. The majority of EG.5 variants sequenced so far also carry a second mutation in their spike protein; these have been named EG.5.1.
A preliminary study from Japan shows that EG.5 is about 20 percent more contagious than even XBB.1.5. This research, led by Kei Sato, a virologist at the University of Tokyo, has not yet been peer reviewed.
Tracking the variant
While EG.5 is still designated a step below variants of concern such as Delta and the Omicron parent, not many positive samples containing EG.5 are currently being sequenced as most people are using at-home tests; further, many states are no longer required to report non-hospitalized cases. This deficiency of genomic surveillance means the scientists and the WHO now have insufficient data to fully assess the impact of prevailing variants.
In the United States, wastewater monitoring and hospitalization data, along with genomic sequences from states such as New York, California, and Florida, provide an indication of the state of pandemic in the U.S.
"Like election projections and exit polls, we can pick some bellwether situations that are still sequencing well," says Rajnarayanan who aggregates the data from all available sources to visualize the daily prevalence of circulating variants. The virus concentration present in samples of wastewater across the United States have tripled since the end of June.
Can EG.5 escape the immune system?
It's too early to know if any of the changes in the spike protein can help EG.5 evade prior immunity. Scientists are racing to figure that out.
The study from Japan shows that although EG.5 is more contagious than XBB.1.5. It also shows that synthetic versions created in the lab were less successful in infecting cells in petri dish. While contagiousness of a virus depends on its spread from one infected person to others; the infectivity of virus measures how many cells the virus can infect in a petri dish. If the Japanese study is correct, the faster spread of the new EG.5 variant is probably not because these viruses are more infectious. The study also shows that EG.5 can still be suppressed by the immunity gained from a previous infection by XBB subvariant.
However, Sato's results conflict with another preliminary analysis of a synthetic EG.5 virus created in the lab of Yunlong Cao of Peking University in China, which suggests the new variant might be able to evade prior immunity from the original Omicron BA.5 or XBB. A second preliminary study by Cao, also not yet peer reviewed, shows that EG.5-like spikes created in the lab-synthesized viruses help them dodge or weaken XBB.1.5 antibodies.
Only more data and peer scrutiny will determine which conclusion is correct.
Are the current boosters effective?
Experts agree that current vaccines and the proposed fall booster will prevent serious complications from COVID-19, even if the new variants might weaken them a little. "Many people assume that vaccines prevent infection," says Sato. They don’t. "The main purpose of vaccination is to reduce the severity” of disease.
The new COVID-19 booster vaccine is designed to target XBB.1.5, which was the prevailing variant until recently. The boosters are expected in early October, according to the CDC director.
“EG.5 is not that different from the immune system’s point of view from XBB.1.5,” says Rasmussen. Despite some differences in the spike protein, EG.5 and other Omicron variants are more or less similar to each other. “XBB.1.5 monovalent booster is going to have broad protection against EG.5 or whatever XBB derived subvariant would be circulating in fall.”
So, that means the booster dose will probably still work well in preventing severe disease. "The most important part is that a booster can keep us healthy, till winter is gone," says Cao.
Is this more dangerous?
WHO says there is no indication yet that EG.5 causes more severe disease. Based on the available evidence, WHO thinks that public health risk posed by EG.5 is currently similar to that of other recent COVID variants of interest.
However, because EG.5 is undoubtedly spreading fast and may even potentially dodge previous immunity, it can still upend the trajectory of the pandemic through a fall surge in cases leading to higher risks for vulnerable populations. For example, the number of COVID cases among the nursing home residents has continued to climb since the end of May, and are now nearing the levels seen at peak of summer 2021—when Delta was the dominant variant.
People who are generally at higher risk—the immunocompromised, those with some pre-existing comorbidity, or people who are either unvaccinated or are not up to date on their vaccines—are still vulnerable to a highly contagious variant, such as EG.5, says Rasmussen.
"The most vulnerable need to be lining up to get the vaccines” [if they haven’t gotten one], and the new booster when it is available," says Rajnarayanan.