A Timeline of COVID-19 Variants

The first strain of SARS-CoV-2, the virus that causes COVID-19, was detected in Wuhan, China in December 2019. At that time, it was called the L strain.

Once the virus was out in the world infecting human hosts, it had plenty of opportunities to start changing. Each time the virus made copies of itself (replicated), it had a chance to make errors in its genes and undergo changes (mutations). 

It didn’t take long for COVID to start mutating enough that variants of the original virus emerged.

To keep track, the World Health Organization (WHO) started to give each variant that it was keeping an eye on (deemed “variant of interest,” “variant of concern,” or “variant being monitored”) a name using the Greek alphabet.

Here’s a look at the most notable strains and variants of the COVID virus throughout the pandemic. 

B.1.1.7 (Alpha)

By the end of 2020, the original L strain of the COVID virus had gone through multiple mutations, including the S, V, and G strains.

The first highly publicized variant—B.1.1.7, then called Alpha—showed up in the United Kingdom in September 2020. 

Alpha caused a surge of COVID infections around the world, starting before any vaccines were available. This variant was more deadly than the original strain of the COVID virus.

The most common symptoms of B.1.1.7 were similar to those reported with the original strain and included loss of taste or smell, fever, dry coughs, shortness of breath, headache, sore throat, congestion or runny nose, nausea or vomiting, and diarrhea.

The three major vaccines against COVID—Pfizer, Moderna, and J&J—all were effective against Alpha.

B.1.351 (Beta)

Shortly after Alpha was discovered, the Beta variant of the COVID virus (B.1.351) was identified in South Africa. It quickly spread to other countries. 

An estimate cited by the Centers for Disease Control and Prevention (CDC) suggested that the Beta variant was about 50% more transmissible than the original strain of the COVID virus, it only ever accounted for a very small percentage of the overall cases in the United States.

The three main vaccines offered in the U.S.—Pfizer, Moderna, and J&J—were effective against Beta.

P.1 (Gamma)

P.1, the Gamma variant of the COVID virus, was first identified in Brazil in November 2020.

Gamma was not responsible for many COVID cases in the U.S. 

In the fall of 2021, the CDC noted that there appeared to be a risk for “breakthrough” COVID infections in people who had been fully vaccinated.

Although data on the Gamma variant was limited, experts did not see evidence that it was as transmissible as the Alpha variant or the upcoming Delta.

B.1.427 and B.1.429 (Epsilon)

In July 2020, researchers identified a new variant in Southern California. The WHO called it Epsilon, and it included B.1.427 and B.1.429. By the fall, experts considered it one of the variants to monitor. 

The main concern with the Epsilon variant was that the mutations in the spike protein would make it able to get around the antibodies people had from a previous COVID infection or a vaccine and that it would spread more easily.

Similarly, there were concerns that antibody treatments for COVID would not be as effective.

B.1.617.1 (Kappa)

B.1.617.1 was dubbed the Kappa variant. It was first detected in India in the fall of 2020. It spread to other countries and the WHO considered it a Variant Under Investigation.

However, global public health experts did not consider it to be a major variant of concern. As of fall 2021, the WHO deemed it a variant to monitor.

Most of the reported cases of COVID linked to the Kappa variant were in India.

Research suggested that vaccines were at least somewhat effective against Kappa.

C.37 (Lambda)

C.37 was called the Lambda variant. It was first identified in Peru in December 2020. It spread to other countries, including the U.S., but did not account for as many cases as other circulating variants.

As with other new strains, the main concerns were that the Lambda variant would spread more easily, cause more severe illness, and resist vaccines and treatments.

B.1.525 (Eta)

B.1.525, the Eta variant, was first detected in the UK and Nigeria in December 2020. 

It did not account for as many cases as other circulating variants, and researchers were not sure what the implications of the changes in the virus would be in terms of transmissibility and immunity.

B.1.621, B.1.621.1 (Mu)

B.1.621/B.1.621.1, or the Mu variant, was identified in Colombia in January 2021 and deemed a variant of interest by the WHO in late summer.

Outbreaks related to Mu were mostly in South America and Europe, though it eventually spread to other countries including the U.S.

B.1.526 (Iota)

B.1.526, called the Iota variant, was first identified in NYC in February 2021. The main concern with this variant was that it was spreading more easily and making people a lot sicker, carrying a higher COVID mortality rate than other variants.

P.2 (Zeta)

P.2, the Zeta variant, was identified in Brazil in February 2021. It was a variant of interest, but not a variant of concern. When it did not spread further, the WHO dropped the variant of interest designation.

B.1.617.2 (Delta)

B.1.617.2, known as the Delta variant of the COVID virus, hit hard in the spring of 2021. It first became the dominant variant in India and spread to over 130 countries, causing a deadly wave of COVID infections worldwide.

Multiple studies showed that the Delta variant caused more severe disease and hospitalizations in unvaccinated people than other variants.

Although the U.S. had launched a COVID vaccination campaign, the Delta variant was able to evade vaccine-induced immunity.

According to a report published in Morbidity and Mortality Weekly Report, more than 70% of infections occurred in people who were fully vaccinated (breakthrough cases).

The surges prompted health authorities around the world to urge people to get a booster vaccine.

The most common symptoms of the Delta variant were headache, sore throat, runny nose, and fever.

B.1.1.529 (Omicron)

The original Omicron variant, was identified in late November 2021 and overtook Delta as the dominant variant within a month.

The highly mutated variant was highly transmissible, but some studies showed that it caused milder infections and people were less likely to be hospitalized with COVID if they were infected with the strain.

The most common symptoms of the Omicron variant were cough, fatigue, congestion or runny nose, and fever.

Omicron BA.1 and BA.2

Omicron subvariant BA.1 closely followed B.1.1.529. When BA.2 was first reported, the media dubbed it a “stealth” variant because it was hard to detect and track. 

The WHO said that BA.2 had a “growth advantage” over the original Omicron variant. Omicron BA.2 started spreading more in the northeastern U.S. around March 2022.

The most common symptoms of BA.1 and BA.2 were similar to those of B.1.1.529.

Similar to problems with earlier variants, breakthrough infections in people who were fully vaccinated were noted by the CDC.

Vaccine makers started working on updated versions of their vaccines and more than one booster was suggested for most people.

Omicron BA.2.12.1

As an offshoot of the Omicron BA.2, the BA.2.12.21 variant accounted for a majority of the new cases in the northeastern U.S. by May 2022.

BA.2.1.2.1 had about 20 of the same mutations that were in the original Omicron, as well as seven new ones. 

The strain was thought to be more transmissible than the variants before it, but the infection seemed to mostly stay in the upper respiratory tract instead of moving deeper into the lungs.

Omicron BQ.1 and BQ.1.1

As of October 2022, BQ.1 and BQ.1.1—which came from BA.5—accounted for more than 16% of COVID cases in the U.S.

Bivalent boosters were shown to offer protection against these subvariants because they are part of the BA.5 family.

However, COVID treatment was a different story: early research showed that monoclonal antibody drugs like Evusheld were not as effective.

Omicron BA.4 and BA.5

Omicron BA.4 and BA.5 showed up in the U.S. around May 2022.

Early data suggested that the two subvariants could evade immune defenses better than earlier versions of Omicron, causing reinfections even in people who had received a booster shot or had recently recovered from COVID.

In anticipation of another surge of infections, the Food and Drug Administration (FDA) authorized Pfizer’s and Moderna’s bivalent booster shots in September 2022. The reformulated booster shot was able to target the original strain and the Omicron subvariants, including BA.4 and BA.5.

In March 2023, the European Centre for Disease Prevention and Control announced it had de-escalated BA.2, BA.4, and BA.5 from its list of SARS-CoV-2 variants of concern (VOC). As of August 2023, no variants are listed as variants of concern. 

As of the end of August 2023, the WHO has listed 3 Omicron variants as variants of interest. There are also several other Omicron variants under monitoring. Again, no variants had been deemed variants of concern (VOC). 

Omicron XBB and XBB.1

XBB variants of Omicron began circulating in late summer 2022. The main concern was that the particular mix of variants (nicknamed Kraken) would make the virus spread more easily and that it would be able to evade vaccines.

Research indicated that XBB had mutated in a way that made the virus able to bind to cells more easily, which would make it more transmissible. It also did appear to be more resistant to antibodies from a previous infection or a vaccine.

The symptoms of XBB variants were similar to other Omicron variants—mainly, cough and congestion. Unlike the earliest COVID variants, XBB wasn’t as likely to cause loss of taste and smell.

Omicron XBB.1.5

By March 2023, the WHO provided an update on its monitoring of XBB variants—specifically, XBB.1.16, which was similar to XBB.1.5. Researchers are keeping an eye on new variants that could become concerns, including XBB.1.16 (“Arcturus”), BF.7, BN.1, and BF.11.

Omicron’s newer variants have been broken down even more as new mutations have cropped up.

XBB.1.5 has some mutations—including EG.5, FL.1.5.1, XBB.1.16.6, and FE.1—that are being monitored under this umbrella. According to WHO data, these COVID mutations appear to be similar to previous ones in terms of how sick they make people and other illness-related factors. One exception is that they may have a higher impact on immunity. 

Omicron XBB.1.16 - "Arcturus" 

In April 2023, the WHO released its first risk assessment for XBB 1.16, which had first been noted in January. In April, it was deemed a variant of interest because case numbers around the world attributed to it were ticking up.

It did not appear that XBB.1.16 was causing more severe illness than XBB1.5, though it did seem likely that it could become a dominant variant. 

In an updated risk assessment in June 2023, the WHO reaffirmed that XBB.1.16 appeared to pose a similar risk as previous XBB variants. Looking at global case numbers, though, the WHO noted XBB.1.16 had become one of the fastest growing variants. Research suggested that again, XBB1.16 did not appear to cause more severe illness, and it seemed to be responsive to current antiviral treatments. 

Omicron EG.5 - "Eris"

Nicknamed Eris, EG.5 has emerged as one of the dominant variants being tracked by the CDC. In July 2023, the WHO considered it a variant under monitoring. It’s closely related to the XBB variants, so researchers think it’s likely that updated vaccines and current treatments that were designed with similar Omicron variants in mind should work against Eris, too. 

On August 9, the WHO "upgraded" Eris to being a variant of interest, as it appeared to have the potential to spread globally and lead to an uptick in cases.

Researchers are not yet sure if Eris is causing more severe illness or is spreading more easily than previous, similar variants. 

Omicron BA.2.86 - "Pirola" 

On August 23, 2023, the CDC gave an update on BA.2.86—nicknamed Pirola—a variant that has been detected in the U.S., as well the UK, Denmark, India, and South Africa. 

One of the reasons researchers are particularly interested in the variant is that it has a lot of mutations compared to previous variants, and it’s not yet clear what that will mean. 

Current COVID tests appear to be capable of picking up BA.2.86. It’s possible that it can infect people who have already had COVID or have been vaccinated more easily than other variants. However, since the variants are still new and so few cases have been detected, researchers are still learning about its transmissibility. 

With updated boosters and vaccines coming in the fall, it’s thought that people will be able to get protected by ensuring they are up to date on their COVID shots. Research suggests that COVID treatments may work against BA.2.86.

So far, there is no evidence that BA.2.86 is making people sicker, but researchers say more data is needed to know for sure. 

Omicron BA.2.75.2 - "Centaurus"

Omicron BA.2.75, XBB.2.3, XBB.1.9.2, and XBB.1.9.1 are also variants under monitoring. Of these, BA.2.75.2—a subvariant of a subvariant that’s already been nicknamed Centaurus—stands out as being an interesting addition to the list—not because there are a lot of samples so far (the WHO only had 3 sequences as of August 2023) but because it’s got a lot of mutations compared to previous variants. 

Researchers are watching closely and studying the variants to see if they can better understand how the mutations might affect their transmissibility, ability to cause severe illness, and resistance to vaccines and treatments. 

Early data that still needs to go through peer-review suggests that BA.2.75.2 might emerge as a tougher variant in terms of evading immunity from previous infection and vaccines, and possibly resisting current treatments (except for one of the newer options, bebtelovimab, which appeared to neutralize the variant). 

However, a study from last September had suggested that antiviral treatments like Paxlovid did seem effective against BA.2.75. Researchers are still waiting on data that would show how vaccines will stack up against BA.2.75.2, as updated boosters won’t be available until the fall.

HV.1 and FL.1.5.1

In September 2023, two XBB variants, HV.1 and FL.1.5.1 ("Fornax"),calso started ticking up. Like EG.5, FL.1.5.1 appeared to have a mutation that made it spread more easily.

The fall also brought another XBB variant, HV.1, to the forefront. By November, accounted for about one-quarter of COVID infections in the U.S. It overtook EG.5, which had been dominant over the summer.

JN.1

In December, the CDC announced it was tracking a new variant, JN.1, which was closely related to
BA.2.86. The variant appeared to be either more transmissible or better at evading immunity, but the CDC did not think it was more of a public health risk than any other circulating variants.

As of the beginning of December, the CDC estimated that JN.1 accounted for 15–29% of the COVID infections in the U.S. and expected that the number would increase as cases continued to pick up over the holidays.

On December 19, the WHO announced it was classifying JN.1 as a variant of interest separate from BA.2.86. According to the WHO, although research suggests that the public health risk posed by JN.1 is still low, the variant "could increase the burden of respiratory infections in many countries" during the winter months.

This article contains the most current information at the time of the most recent update, but the COVID virus is still evolving. New variants of concern will be added according to reports by the WHO and the CDC.