According to the most recent Centers for Disease Control and Prevention estimates, EG.5 is responsible for around 17% of new Covid-19 cases in the United States.

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EG is a variant of the Omicron family's XBB recombinant strain and, unlike the original, it reflects another gradual change to the virus, not a serious evolutionary leap. 

It has one more mutation to its spike, at position 465, as compared to its progenitor XBB.1.9.2. This mutation has already been found in other coronavirus strains.

EG.5 has a new offshoot, EG.5.1, which adds a second mutation to the spike. This one is also fast expanding. Dr. David Ho of Columbia University has been evaluating these mutations in his lab to assess the resistance of antibodies to the mutations.

In an email to CNN, Ho explained that both mutations were "only slightly more resistant to neutralizing antibodies in serum of infected and vaccinated persons," adding that clinically they are not more severe than symptoms of variants that preceded them.

According to Dr. Eric Topol, a cardiologist at the Scripps Translational Research Institute, the new variant has "some more immune escape compared to the ones that were precedents in this XBB series," which he believes is an advantage allowing it to spread.

The variant has reached Ireland, France, the UK, Japan, and China.

The World Health Organization elevated it from a variety under surveillance to a variant of interest on Wednesday, indicating that the organization believes it should be researched and examined further.

Epidemiologists believe changes in temperatures and summer travel carrying the virus to new victims, as well as air conditioning due to record heat, can be blamed for the variant's rapid spread.

Dr. Anne Hahn, a postdoctoral associate in the Department of Epidemiology of Microbial Diseases at the Yale School of Public Health, believes that what the variants will bring in colder weather is still unknown. 

Dr. Dan Barouch, an immunologist and virologist at Harvard University in Boston warns that those at severe risk of diseases should continue "to take precautions," believing new infections will be mild, even if widespread.

Topol believes that the revised Covid-19 booster, which will be aimed against the XBB version this autumn, will be a very close match to the variations already circulating, including EG.5, and that it will provide good protection – assuming regulatory agencies can deliver it to patients in time.

Vaccination producers have stated that the new injections will be accessible in a few weeks, but CDC Director Dr. Mandy Cohen has predicted that the improved vaccination will be available in October since it will require additional approval from the FDA and CDC.

Topol stressed the need for the elderly and those with weakened immune systems to take the vaccine, warning that the US cannot delay the vaccine rollout due to a possibility of variants after EG.5 that may bind closer to cells, making them more dangerous than previous variants.