COVID variant

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.

Strains vs. Variants

Strains and variants are different. A variant is when a virus changes (mutates) from the original version—for example, an error in the genetic code happens when the virus is replicating.

  • A variant is like a new “take” on the original virus. 
  • A strain is when a virus has so many variants that it starts acting differently—for example, it’s much more transmissible than the previous version. 

All strains are variants, but not all variants are new strains. 

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

Alpha (B.1.1.7)

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—Alpha (B.1.1.7)—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.

Beta (B.1.351)

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.

Variants and Long COVID

Lasting symptoms after a COVID infection—called “long COVID” or post-COVID conditions—have been linked to different risk factors, including age and vaccination status.

Some research suggests that some variants might be more likely to lead to long COVID symptoms than others.

For example, infection with Omicron might be less likely to lead to long COVID than infection with earlier variants.

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.

Epsilon (B.1.427 and B.1.429)

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.

Kappa (B.1.617.1)

The Kappa variant (B.1.617.1) 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.

Lambda (C.37)

The Lambda variant (C.37) 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.

Eta (B.1.525)

The Eta variant (B.1.525) was first detected in the UK and Nigeria in December 2020. 

It didn’t 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.

Mu (B.1.621, B.1.621.1)

The Mu variant (B.1.621, B.1.621.1) 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.

Iota (B.1.526)

The Iota variant (B.1.526) 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.

Zeta (P.2)

The Zeta variant (P.2) 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.

Delta (B.1.617.2)

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.

Delta Plus

Delta AY.4.2 was an offshoot of the Delta variant—not a variant on its own. It was also called “Delta Plus,” though many experts did not think the name was appropriate and refrained from using it. 

Delta AY.4.2 had two mutations on its spike protein, which helped the virus to enter and infect cells. The mutations appeared to make it 10%–20% more transmissible.

AY.4.2 was responsible for a surge of COVID cases in the UK but did not take hold in the U.S.

Omicron (BA.1)

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.2

When the Omicron subvariant 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.2 were similar to those of BA.1.

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. 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 October 2021, researchers in France found a new COVID variant deemed B.1.640.2. It was not deemed to be a variant of concern by the WHO because it had not infected very many people. 

The most common symptoms of B.1.640.2 were sore throat, cough, and a hoarse voice.

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.

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.

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.

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.

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