Will COVID-19 variants keep getting worse?

The highly contagious Delta variant is now responsible for the vast majority of COVID-19 cases in the United States. How might the virus next evolve?

What is a variant?

Viruses are constantly mutating. Most mutations are relatively harmless and do not affect a virus' properties, but some mutations can make a disease more infectious or severe. When it comes to COVID-19, the World Health Organization and U.S. Centers for Disease Control and Prevention are tracking variants of interest (VOIs) and variants of concern (VOCs). A VOI is suspected of being more contagious, capable of causing more severe disease, and/or reducing vaccine effectiveness than an original strain; a VOI becomes a VOC when there is evidence to support these suspicions. There are four known VOCs: Alpha, which was first identified in the United Kingdom; Beta, first identified in South Africa; Delta, first identified in India; and Gamma, first identified in Japan and Brazil.

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Why am I hearing so much about the Delta variant?

Because of its alarmingly rapid spread. The Delta variant, which emerged from India's devastating second COVID wave in the spring, became the dominant strain worldwide in a few short months thanks to its high transmissibility. Data shows it is at least twice as contagious as previous variants. People who contracted the original strain tended to spread the virus to three others, on average; models suggest that figure jumps to seven for Delta. Dr. Anthony Fauci, the country's top infectious disease expert, said data shows people who become infected by the Delta variant have viral loads "about 1,000 times higher in quantity" than people who were infected with the Alpha variant. Studies out of Canada and Scotland suggest unvaccinated people infected with the Delta variant are also more likely to be hospitalized than patients with the original virus strain or the Alpha variant. The good news is that so far, the vaccines available in the U.S. remain very effective at preventing severe illness and death, even against the Delta variant. But in areas with low vaccination rates, cases are on the rise and hospitals are filling up.

What is "Delta Plus"?

The Delta Plus variant is related to Delta and has an additional mutation in its spike protein. Dr. Peter Chin-Hong, an infectious disease specialist at the University of California San Francisco, says public health experts believe Delta Plus is "at least as bad as Delta," but they don't have the clinical and biological information necessary to know if it is more transmissible, makes people sicker, or is able to evade vaccines. Right now, it only represents a small fraction of U.S. infections.

Will a variant worse than Delta emerge?

"That's what keeps me up at night," Shweta Bansal, an infectious-disease ecologist at Georgetown University, told The Atlantic. The longer the virus is allowed to spread in unvaccinated populations, the greater the chance of it mutating when jumping from host to host. The big concern is that a new variant will be able to evade the vaccines, and everyone — regardless of their vaccination status — will be vulnerable to the virus once again. We've already seen the virus change several times in the less than two years since COVID-19 emerged. But while scientists are surprised by COVID-19's rapid mutations, there are evolutionary pressures on how viruses change. When an organism evolves to become more fit in one way, it often sheds a different trait at the same time. For example, a virus might mutate to become more contagious, but at the expense of its own severity. Such evolutionary trade-offs help keep many viruses in check. "There isn't a super-ultimate virus that has every bad combination of mutations," Dr. Aris Katzourakis, who studies viral evolution at the University of Oxford, told BBC.

Do vaccines prevent new variants?

Not necessarily. The COVID-19 vaccination program will "squeeze [the virus] in another evolutionary direction," BBC writes. But history suggests the vaccines will give us an advantage: "Many viruses — measles, mumps, rubella, polio, smallpox — have never meaningfully circumvented their vaccine," writes Dhruv Khullar at The New Yorker. The WHO expects that, as more people are vaccinated, circulation of the virus will decrease and mutation will slow. But right now, with just 16 percent of the world fully vaccinated, the virus still has plenty of opportunity to change and evolve. While the global vaccination program continues at a snail's pace, public health experts are encouraging other mitigation strategies be used slow the spread of the virus and thus reduce the risk of new variants appearing. Social distancing, masking, and good ventilation all help slow the spread of COVID-19. In a worst-case scenario, the vaccines can be tweaked relatively quickly to target new variants, though early detection is key.

So how are we detecting new variants?

In the United States, there are private and academic labs, hospitals, and state health departments that are sequencing virus genomes to look for new — and potentially serious — variants. However, there isn't much of a coordinated effort, and the CDC doesn't have a public tracker showing virus mutations. The Rockefeller Foundation found that as of early June, only 14 countries were sequencing 5 percent or more of COVID-19 cases. "If new variants emerge in a country where there isn't much genome sequencing, it could be a real problem," Brendan Larsen, a PhD student at the University of Arizona who identified a new variant earlier this year, told BBC. That's why people in every corner of the globe must continue to get tested regularly, Ed Yong writes in The Atlantic. Sequencing will be important throughout the entire pandemic, even when transmission finally slows down, because at that point, the virus' movements will become "harder to predict," Yong said.