Variants of Coronavirus

What Is a COVID-19 Variant?

Viruses are always changing, and that can cause a new variant, or strain, of a virus to form. A variant usually doesn’t affect how the virus works. But sometimes they make it act in different ways.

Scientists around the world are tracking changes in the virus that causes COVID-19. Their research is helping experts understand whether certain COVID-19 variants spread faster than others, how they might affect your health, and how effective different vaccines might be against them.

How Many Coronaviruses Are There?

Coronaviruses didn’t just pop up recently. They’re a large family of viruses that have been around for a long time. Many of them can cause a variety of illnesses, from a mild cough to severe respiratory illnesses.

The new (or “novel”) coronavirus that causes COVID-19 is one of several known to infect humans. It’s probably been around for some time in animals. Sometimes, a virus in animals crosses over into people. That’s what scientists think happened here. So this virus isn’t new to the world, but it is new to humans. When scientists found out that it was making people sick in 2019, they named it as a novel coronavirus. Experts call these strains SARS-CoV-2.

How Do Variants Happen?

Coronaviruses have all their genetic material in something called RNA (ribonucleic acid). RNA has some similarities to DNA, but they aren’t the same.

When viruses infect you, they attach to your cells, get inside them, and make copies of their RNA, which helps them spread. If there’s a copying mistake, the RNA gets changed. Scientists call those changes mutations.

These changes happen randomly and by accident. It’s a normal part of what happens to viruses as they multiply and spread.

Because the changes are random, they may make little to no difference in a person’s health. Other times, they may cause disease. For example, one reason you need a flu shot every year is because influenza viruses change from year to year. This year’s flu virus probably isn’t exactly the same one that circulated last year.

If a virus has a random change that makes it easier to infect people and it spreads, that variant will become more common.

The bottom line is that all viruses, including coronaviruses, can change over time.


Coronavirus Mutations

Alpha (B.1.1.7) . In late 2020, experts noted gene mutations in COVID-19 cases seen in people in southeastern England. This variant has since been reported in other countries, including the U.S. Scientists estimate that these mutations could make the virus up to 70% more transmissible, meaning it could spread more easily. Some research has linked this variant to a higher risk of death, but the evidence isn't strong.

The mutation on the Alpha variant is on the spike protein, which helps the virus infect its host. This is what COVID-19 vaccines target. These vaccines make antibodies against many parts of the spike protein, so it’s unlikely that a single new mutation in the Alpha variant will make the vaccine less effective.

Beta (B.1.351). Other variants of the virus have been found in other countries, including South Africa and Nigeria. The Beta variant appears to spread more easily than the original virus but doesn’t seem to cause worse illness.

Gamma (P.1). In January 2021, experts spotted this COVID-19 variant in people from Brazil who’d traveled to Japan. By the end of that month, it was showing up in the U.S.

The Gamma variant appears to be more contagious than earlier strains of the virus. And it may be able to infect people who've already had COVID-19. A report from Brazil confirms that a 29-year-old woman came down with this variant after an earlier coronavirus infection a few months before.   

Some early research suggests that the variant’s changes might help it evade antibodies (made by your immune system after an infection or a vaccine) that fight the coronavirus. A lab study shows that the Pfizer-BioNTech vaccine can neutralize the fast-spreading Brazil strain. But more research is needed.

Delta (B.1.617.2). This variant was spotted in India in December 2020. It caused a huge surge in cases in mid-April 2021. This highly contagious variant is now found in 43 countries including the U.S., the U.K., Australia, and Singapore. It's the dominant strain in the U.S. and the U.K.


A study of the COVID-19 vaccine’s effectiveness against this variant found that:

  • Two doses of the Pfizer-BioNTech vaccine were 88% effective 2 weeks after the second dose.
  • Two doses of the AstraZeneca vaccine available in the U.K. were 60% effective.
  • Both vaccines are only 33% effective 3 weeks after the first dose.

Given the difference in protection between doses, experts recommend getting the second shot as soon as you’re eligible.

Research suggests that changes to the spike protein may make the Delta variant up to 50% more transmissible than other COVID-19 variants.

For people who haven’t had the coronavirus vaccine, the Delta variant may cause more severe illness than the original strain of the virus. Vaccinated people may also get what’s called a “breakthrough infection,” but they’re less likely to be seriously sick or to die. The relatively low rate of vaccination in some areas of the country is the main reason that the Delta variant has been able to spread so rapidly and shows no signs of slowing down. Getting the vaccine is the best way to slow the spread of the coronavirus and protect yourself against serious illness or death.  

Mu (B.1.621). Experts first spotted this COVID-19 variant (pronounced m’yoo) in Colombia in January 2021. Since then, countries in South America and Europe have reported outbreaks of Mu.

In the U.S., the CDC says Mu reached a peak in June 2021, when it made up less than 5% of variants going around the country. As of early September, it had been steadily declining.  

Still, scientists continue to track Mu. The World Health Organization (WHO) says this variant has mutations that might make COVID-19 vaccines and our immune systems less effective against it. Early data suggests it has certain similarities to the Beta variant, but we need more research to know for sure.

In August 2021, the WHO labeled Mu a “variant of interest.” In general, variants of interest might pose an emerging risk to the world’s public health, with the potential to do things like spread more easily, cause worse disease, or evade vaccines or tests. But they’re considered less of a threat than “variants of concern,” like Alpha, Beta, Gamma, and Delta.


As of September 2021, the CDC hadn’t escalated Mu to being a variant of interest in the U.S. The agency intends to keep tracking it along with the other variants.

R.1. Scientists first detected R.1 in a number of countries, including Japan. There was an outbreak at a Kentucky nursing home in March 2021, when an unvaccinated health care worker passed it to about 45 other staff and residents.

The WHO labeled it a “variant under monitoring” in April 2021, meaning some of its characteristics may pose a future risk to humans.

As of September 2021, the CDC hadn’t labeled R.1 as a variant of concern or interest.

Earlier Coronavirus Variants

Earlier in 2020, when the pandemic was new, you might have heard that there was more than one strain of the new coronavirus. Is it true? The answer appeared to be yes.

The theory about different variants of the new coronavirus came from a study in China. Researchers were studying changes in coronavirus RNA over time to figure out how various coronaviruses are related to each other. They looked at 103 samples of the new coronavirus collected from people, and they looked at coronaviruses from animals. It turned out that the coronaviruses found in humans weren’t all the same.

There were two types, which the researchers called “L” and “S.” They’re very similar, with slight differences in two places. It looks like the S type came first. But the scientists say the L type was more common early in the outbreak.

What to Expect

The virus that causes COVID-19 will probably keep changing. Experts may find new variants. It’s impossible to predict how those virus changes might affect what happens. But change is just what viruses do.

WebMD Medical Reference Reviewed by Neha Pathak, MD on September 22, 2021



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