Microscope image of virus

The emergence of faster-spreading variants of the coronavirus has increased concern about the virus’s path just as the vaccines that many hope will bring an end to the pandemic are being distributed.

There are at least five concerning variants now spreading in the U.S., according to the Centers for Disease Control and Prevention. Plus, there are many other lesser-known variants that researchers are tracking, including a number that have emerged within the U.S., according to Jay Butler, deputy director for infectious diseases at the CDC.

The five variants the CDC considers most concerning—which first emerged in the U.K., South Africa, Brazil, and California—are either more transmissible, more likely to cause severe disease, less treatable with current COVID-19 treatments, or better at evading the antibodies generated by vaccination or a previous infection. Some have a combination of those traits.

With these variants on the rise, Americans should prepare for a possible COVID-19 resurgence in the coming months, according to a Johns Hopkins Bloomberg School of Public Health report released Feb. 16, which analyzed current variants of concern as well as those that may be problematic in the future. Cases and deaths have started to rise again, according to CDC Director Rochelle Walensky, speaking at a press briefing March 29. 

Here are answers to questions you may have about these coronavirus variants.

Why Do Viruses Mutate?

Infectious disease experts say viruses always mutate. This virus is no different, acquiring and losing genetic traits as it spreads.

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Viruses such as SARS-CoV-2, which causes COVID-19, make imperfect copies of themselves as they move from person to person or from an animal to a person. This leads to constant mutations and new variants, says Peter Katona, MD, an infectious disease specialist and clinical professor of medicine at the David Geffen School of Medicine at UCLA. The term “variant” describes a version of the virus with a specific set of mutations.

These mutations often don’t provide any advantage to the virus. But sometimes a mutation can make a virus more transmissible or change the severity of the disease the virus causes. When the same mutation emerges in multiple places, as has been seen with aspects of variants first detected in South Africa and Brazil, it could indicate that these mutations provide some advantage for the virus—making it easier to spread or to evade antibodies, for example.

What Concerning Variants Are on the Rise?

The SARS-CoV-2 virus first emerged in China and continued to mutate as it spread around the globe. A variant of that virus that was probably more contagious emerged in Europe, Katona says. That variant’s infectiousness helped it spread rapidly throughout Europe and the U.S., where it became one of the most dominant variants.

One of the variants now causing the most alarm—referred to as B.1.1.7—was first found in England.

This variant has a large number of mutations, according to a report from the European Centre for Disease Prevention and Control (ECDC), including changes to the spike protein that the coronavirus uses when infecting cells. The CDC estimates this variant is approximately 50 percent more contagious and causes more severe illness.

The latest data indicates this variant is more than 30 percent more likely to cause severe illness (PDF).

Even if a variant does not cause more severe disease, a more infectious variant would still lead to more deaths and severe cases in the long run because cases could grow exponentially, putting already strained hospital systems under further pressure, says Gregory Poland, MD, a professor of medicine and infectious diseases, and director of the Vaccine Research Group at the Mayo Clinic.

The major concern with the variants that emerged in South Africa and Brazil, which were both detected in the U.S. in January, is that that the mutations may have made them better at avoiding the antibodies that can fight off the coronavirus. This could make vaccines less effective and increase the likelihood of reinfection.

For the same reason, some monoclonal antibody treatments for COVID-19—which mimic the natural antibodies created by the immune system to fight infection—are less effective against these variants. The variant identified in South Africa is also about 50 percent more transmissible, like B.1.1.7.

A number of studies in South Africa have found that some vaccines are less effective at stopping infections with the B.1.351 variant that emerged there, though it does appear that vaccines are still able to prevent severe disease with these infections. And Pfizer and BioNTech announced April 1 that the vaccine created by those companies is just as effective in South Africa as it has been elsewhere, which is encouraging, though it still needs to be studied further.

Several recent preliminary studies from Brazil raise similar concerns that the P.1 variant first discovered there can evade immunity from prior infections. One study found that antibodies that should help prevent infection were much less effective at stopping the P.1 variant. Another early study estimated that this variant is 1.4 to 2.2 times more contagious, and that the variant’s antibody-evading properties could help it reinfect between 25 and 61 percent of previously infected people.

Those factors could help explain why the Brazilian city of Manaus recently experienced another surge of COVID-19, even though many researchers thought there had already been enough infections there to provide herd immunity.

Two other concerning variants were first identified in California. These two, B.1.427 and B.1.429, are both about 20 percent more contagious than previous forms of the virus, according to the CDC. They’re also somewhat less susceptible to the antibodies created by vaccination, and significantly less treatable with monoclonal antibodies.

Where Are These Variants Spreading?

Cases of the B.1.1.7 variant first emerged in the U.K. in September, primarily in southeast England, according to the ECDC and the CDC. By December, cases were also identified in Wales, Denmark, Belgium, the Netherlands, Australia, Canada, and dozens of other countries. B.1.1.7 has now been detected in as many as 114 countries

The first known case in the U.S. was identified Dec. 29 in Colorado, in someone with no travel history. Within days, additional cases began popping up in other states.

As of March 4, there have been more than 11,569 cases of B.1.1.7 identified in about 51 U.S. states and territories, though many more are probably undetected. In a preliminary study released Feb. 7, researchers confirmed that B.1.1.7 cases were doubling in the U.S. every 10 days, confirming CDC projections from January that this variant is on track to become the dominant U.S. variant sometime in March.

The U.S. does less routine virus sequencing than some other countries, including the U.K., which makes it more difficult to know how widespread the variant may be here. (Sequencing is the kind of analysis scientists do to determine the variant of a virus causing a particular case or a particular outbreak.) By late December, viruses had been sequenced in just 51,000 of the 17 million COVID-19 cases in the U.S., according to the CDC.

“I would not be surprised of the existence of additional novel strains within the populace, ones that have yet to be identified,” says James Dickerson, PhD, chief scientific officer at Consumer Reports. 

Public health officials are ramping up their sequencing efforts, Butler says. On Feb. 17, the White House announced that the CDC would invest $200 million to increase sequencing from about 7,000 samples per week to approximately 25,000. If the U.S. can reach that target, it should help provide a clearer picture of how widespread the variant is in the U.S.

The variant that was first detected in South Africa has been found in at least 68 countries, with at least 312 cases detected in the U.S. The variant that first emerged in Brazil has been found in at least 36 countries, with at least 172 cases detected in the U.S.

As of March 13, the CDC estimates that over 40 percent of COVID-19 cases in the U.S. are caused by either the five concerning variants or one of several other potentially concerning variants the agency is tracking, up from less than 10 percent at the beginning of 2021. The two California variants make up almost 60 percent of cases in that state, and more than 30 percent of cases in Arizona and Nevada.

Which Variants Have Emerged in the U.S.?

In addition to the already described variants, often called “variants of concern,” researchers are also tracking many other variants of the virus.

In many cases, it’s not yet clear whether the mutations observed in lesser-known variants will help or harm the virus’s ability to spread. But some data does raise concerns about several of the potential variants that have emerged in the U.S.

The California variants are not the only ones first detected in the U.S. that have raised questions. A preliminary study published Feb. 14 identified seven virus variants in the U.S. with the same mutation in the spike protein the virus uses to infect human cells. Though more research on these variants is needed, it’s possible that the parallel evolution of the same mutation means this mutation makes it easier for the virus to spread.

At the end of February, yet another new variant that may potentially be able to evade previously acquired immunity appeared to be spreading in New York City, according to several preliminary studies. One of the mutations in this variant is the same as the mutation that’s thought to be at least partly responsible for making vaccines less effective in South Africa, though it’s not yet clear how this variant will affect vaccine efficacy.

Variants will continue to emerge as the virus continues to spread rapidly, according to the authors of the variant report from Johns Hopkins.

Have These Variants Spurred Travel Restrictions?

Yes. On Jan. 26 the U.S. began requiring all airline passengers entering the country to test negative for COVID-19 no more than 72 hours before departure.

President Joe Biden has also extended travel bans restricting non-U.S. citizens from traveling to the U.S. from Brazil, South Africa, the U.K., and at least 27 European countries, according to the New York Times.

How Might Mutations Affect the Vaccine?

Vaccines teach our immune system to respond to a virus by recognizing some key sign of it. Mutations that affect the parts of the virus that the immune system recognizes could undermine a vaccine’s effectiveness.

The first vaccines that were authorized in the U.S. for COVID-19, made by Moderna and a partnership of Pfizer and BioNTech, target a particular protein—the spike protein—that the coronavirus uses to infect people. So mutations of that protein could potentially make a vaccine less effective, Poland says. That’s one potential concern with the variant that emerged in Brazil, according to the CDC. 

A scientific brief from the CDC says “the virus would likely need to accumulate multiple mutations in the spike protein to evade immunity induced by vaccines.” 

Data from trials of vaccines made by Johnson & Johnson and Novavax, however, indicate that these vaccines might not work as well against the new variants.

According to a Food and Drug Administration analysis, the Johnson & Johnson vaccine is 66 percent effective overall at preventing moderate and severe COVID-19. But breaking down data by region shows that efficacy varies against certain virus variants. Research showed that the vaccine was 72 percent effective in the U.S., compared with 64 percent in South Africa, where the B.1.351 variant is the predominant version. The J&J vaccine was 61 percent effective in Latin America, where it was primarily tested in Brazil. Twenty-eight days after vaccination, the J&J vaccine was 86 percent effective against severe disease in the U.S., with similar efficacy in South Africa and Brazil. And no one who received that vaccine needed to be hospitalized because of COVID-19 at least 28 days after vaccination.

Novavax representatives said its vaccine appears to be approximately 89 percent effective overall, based on a trial in the U.K., indicating that the vaccine probably works against the U.K. variant. But in a South African trial, the Novavax vaccine was 49.4 percent effective overall and 60 percent effective for HIV-negative people. 

Though scientists need more data to fully understand just how much the new variants are able to evade vaccine-induced protection, trial results from South Africa do raise concerns, according to John Brooks, chief medical officer for the CDC’s COVID-19 response. Still, even if vaccine efficacy is reduced to 60 percent overall against these variants, that’s still effective enough to help stop the spread of the virus, Butler says. Plus, these vaccines still appear to be very effective at preventing severe disease.

Pfizer’s April 1 announcement that its vaccine is over 90 percent effective in South Africa is encouraging, though that data needs to be confirmed by the FDA and independent scientists. 

Even if there’s some reduction in efficacy, the vaccines are still likely to be highly effective, according to Poland. Still, we may eventually need new vaccines that target other parts of the SARS-CoV-2 virus, Poland wrote in a commentary for the journal Vaccine, where he’s the editor-in-chief. Over time, new variants of the virus could very likely require booster vaccines targeted at those variants.

What Should You Do?

The same advice about stopping the spread of the virus is even more crucial now, with cases peaking and more infectious variants spreading.

“The appropriate action is caution, follow the existing procedures for mask wearing, social distancing, and minimizing the number of potential lines of exposure,” says CR’s Dickerson. Now is a good time to consider upgrading your mask.

The more the coronavirus spreads, the more it mutates, according to Poland and Katona.

“We are needlessly prolonging the duration and the severity of this pandemic by not following a simple hands, face, space paradigm,” Poland says. 

Editor’s Note: This article has been updated to include new information and developments. It was originally published Dec. 22, 2020.