COVID-19 Variants

Details on Specific Variants

Alpha | Beta | Gamma | Delta | Lambda | Mu | Omicron

GISAID Variant Tracker

variant table

What is a virus?

What is a mutation?

What are variants and what are the concerns?

How are variants categorised?

How many variants are there?

Are vaccines effective against the variants?

Is there a need for booster vaccination due to the variants?

Where can I find more information?

What is a virus?

A virus is a collection of genetic code (DNA or RNA) surrounded by a protein coat. Viruses cannot replicate alone; they require host cells. In order to infect host cells, viruses have various adaptations to allow penetration into the host cell. For example, in the case of SARS-CoV-2, there are multiple spikes with receptors and enzymes allowing for binding to, and penetration into, the host cell. Once within the host cell, the virus can then replicate, usually killing the host cell in the process, and causing physical manifestations of disease. Viruses cannot be killed by antibiotics. Vaccines, anti-viral medications, and certain treatments such as monoclonal antibodies are the only pharmaceutical methods to eliminate or reduce the severity of the viral disease. Back to top.

What is a mutation?

Viruses constantly change and evolve through mutation. A mutation is a change to the genetic material of the virus, occurring during replication. Since the genetic material of the virus determines how it infects hosts, mutations can alter numerous things. Some possible changes include increase in transmissibility (how easily it can spread), increase in virulence (how severe it is), immune escape (resistance to vaccines), and reduced effectiveness of some treatments. Back to top.

What are variants and what are the concerns?

A variant is a subtype of a microorganism that is genetically distinct from a main strain, but not significantly different to be a different strain. Using a fruit analogy, think of the variety of apples. Red Delicious, Granny Smith, and Honeycrisp are “variants” of apples. Because the situation is continuing to evolve rapidly, and more variants are expected to emerge, this raises concerns such as how a new variant will affect transmissibility, severity, immune escape and effect of treatments. Other unknowns include the impact on those with pre-existing conditions. Each of these factors can alter the risk to global travel. Back to top.

How are variants categorized?

The WHO is constantly monitoring and assessing new COVID-19 variants. WHO categorises COVID-19 variants in order to prioritise global monitoring and research and inform the ongoing response to the pandemic.

Variant of Concern (VOC): Shows an increase in transmissibility, has an increase in virulence or clinical presentation (symptoms), or a decrease in effectiveness of public health measures such as vaccination, non-pharmaceutical interventions, testing or treatments.

Variant of Interest (VOI): Shows genetic changes that may affect transmissibility, disease severity, immune, diagnostic or therapeutic escape AND has been identified to cause significant transmission, or multiple clusters with increasing prevalence, or other indicators of emerging risk.

Variants under Monitoring (VUM): Those listed in this category are known to have mutations that could present a future risk but evidence of actual impact is unclear requiring further monitoring. These variants also include previously existing variants that no longer meet criteria for VOC or VOI. VUMs also include emerging variants.

VOCs and VOIs may be downgraded to former VOCs/VOIs when they are “conclusively demonstrated to no longer pose a major added risk to global public health compared to other circulating SARS-CoV-2 variants.”

The United States Centre for Disease Control and Prevention (CDC) and European Centre for Disease Control and Prevention (ECDC) also use similar categories. The CDC has one additional category.

Variant of High Consequence (VOHC): clear evidence that prevention measures or medical countermeasures (MCMs) have significantly reduced effectiveness relative to previously circulating variants.

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How many variants are there?

Several variants have already been identified, and as more locations undertake genetic sequencing, more variants will emerge. It is impossible to say how many will emerge during the course of the pandemic. While not all variants are VOI or VOC, it is expected some may be more transmissible, potentially cause more severe disease, and / or evade current vaccines and treatments. Back to top.

Are vaccines effective against the variants?

Vaccination produces a ‘polyclonal’ response that targets several parts of the Spike protein or the virus itself. The virus would likely need to accumulate multiple mutations in the Spike protein or other regions to evade immunity induced by a vaccine. According to the CDC, “So far, studies suggest that antibodies generated through vaccination with currently authorized vaccines recognize these variants. This is being closely investigated and more studies are underway."

The ECDC have also stated: "The COVID-19 vaccines that are currently being rolled out through vaccination programmes are expected to provide at least some protection against new virus variants because they all lead to a broad immune response. If any of these vaccines prove to be less effective against one or more variants, it will be possible to change the composition of the vaccine to protect against those variants."

Regardless, it is vital for communities to have rigorous compliance with non-pharmaceutical interventions in addition to getting vaccinated.

Specific information on vaccine effectiveness and efficacy may be found under each variant.

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Is there a need for booster vaccination with the variants?

Yes. Data has shown significant immune escape in some variants. The available data also shows that vaccination provides some protection, reduced to 30% in some studies, but booster vaccination raised that to approximately 72%.

Many countries have begun to provide booster vaccination to their populations per their vaccination plan.

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Where can I find more information?

The WHO releases a weekly report on the epidemiological situation. The most current report, and archived reports, may be found here.

GISAID Variant Tracker (a project at Scripps Research supported by the National Institute for Allergy and Infectious Diseases, National Center for Data to Health, and Centers for Disease Control and Prevention) has a dashboard of variants. The dashboard allows customisable reports by variant, location and time.

WHO Variant Tracker

CDC Variant Tracker

CDC Global Variant Report Map

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Specific Variants

Variants of concern

Alpha | B.1.1.7

First identified in the United Kingdom in September 2020 and classified as a Variant of Concern on 18 December 2020.

Transmissibility: The Alpha variant has shown 30 to 70% greater transmissibility compared to the wild strain.

Severity: While initially there was no evidence of more severe disease, more recent reports indicate that this variant can lead to an increase in hospitalization and death.

Vaccine Efficacy: Several Vaccine-producing companies (Pfizer/BioNTech, Moderna, Oxford/AstraZeneca, Johnson & Johnson, Novavax) confirmed that their vaccines, based on different designs, can all be effective against this variant.

The Novavax vaccine has shown an efficacy of 89.3% in its Phase 3 clinical trial conducted in the UK. Interestingly, a study published in The New England Journal of Medicine found the Oxford/AstraZeneca vaccine is approximately 75% effective against the Alpha variant. This is in comparison to the overall efficacy prior to the emergence of variants, measured at 66.7%. The same study found that the mRNA vaccines (Pfizer/BioNTech and Moderna), had no reduced efficacy. A second study in The New England Journal of Medicine, found the Pfizer/BioNTech vaccine was 93.7% effective.

Treatment Efficacy: Monoclonal antibody treatments remain effective. Some evidence shows a reduction in efficacy of convalescent plasma.

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Beta| B.1.351

First identified in South Africa in May 2020 and classified as a Variant of Concern on 18 December 2020.

Transmissibility: Evidence has shown approximately 50% greater transmissibility.

Severity: No peer-reviewed evidence showing increased severity.

Vaccine Efficacy: A study published in The New England Journal of Medicine found the Oxford/AstraZeneca vaccine “did not show protection against mild to moderate COVID-19 due to the [Beta] variant.” The same study noted interim results found the Johnson & Johnson vaccine to be 57% effective against moderate to severe COVID-19 and 89% effective against severe cases. The Sputnik V vaccine has reduced efficacy, and one study found Novavax had 60% efficacy in adults that are HIV negative.

Treatment Efficacy: Studies have found that monoclonal antibody treatments, Bamlanivimab and Etesivimab, do not effectively neutralise this variant.

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Gamma | P.1

First identified in Japan and Brazil in November 2020. It was classified as a Variant of Concern on 11 January 2021.

Transmissibility: Some evidence shows this variant is more than twice as transmissible as the wild-type.

Treatment Efficacy: The effects of Bamlanivimab and Etesevimab are significantly reduced against this variant, and it has shown reduced neutralization by convalescent plasma.

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Delta | B.1.617.2

The B.1.617 variant was first identified in India in December 2020. A sub-lineage of this variant, B.1.617.2, was named the Delta variant in May 2021.

Transmissibility: Studies have found almost a 30% increase compared to the wild-type. A study published in the journal Eurosurveillance found a 29% increase in transmissibility compared to the wild-type, and a study in BMJ found a 60% increase in transmissibility compared to the Alpha variant. The CDC notes the Delta variant is nearly twice as contagious as other variants.

Severity: Some evidence has shown a higher frequency of hospitalisation (nearly double), and increased severity associated with this variant.

Vaccine Efficacy: Several vaccine manufacturers (Pfizer/BioNTech, Moderna, Oxford/AstraZeneca. Johnson & Johnson, Novavax) have confirmed that their vaccines, based on different designs, are all effective against this variant. One study in BMJ, found the Pfizer/BioNTech vaccine was 88% effective and the Oxford/AstraZeneca vaccine was 60% effective. Both vaccines have shown greater than 90% efficacy at preventing severe disease requiring hospitalisation.

A study in The New England Journal of Medicine, found the Pfizer/BioNTech vaccine was 88% effective against the Delta strain, mirroring the findings of BMJ. The Oxford/AstraZeneca vaccine was found to be 67% effective.

This variant has also shown immune escape in those who were previously infected with a different strain, but remain unvaccinated. Immune escape has also occurred in people previously vaccinated. The CDC confirms that fully vaccinated individuals can still transmit the Delta variant, though for a shorter period of time than unvaccinated individuals.

Treatment Efficacy: Studies have found reduced efficacy for monoclonal antibodies. At least one unique mutation has been identified as the likely cause in this strain. One study found monoclonal antibody medication Bamlanivimab, had little to no effect on the Delta variant, though Etesivimab, Casirivimab, and Imdevimab remained active.

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Omicron l B.1.1.529

The WHO has published an FAQ and a Technical Briefing. The WHO EURO office has published a Myth vs. Fact.

First detected in South Africa on 24 November 2021 and Botswana shortly after. It was classified as a variant of concern on 26 November and named Omicron on the same day.

Transmissibility: Specific data regarding transmissibility is still lacking as the situation evolves. However, real world evidence has shown Omicron to be much more highly transmissible compared to the wild-type and past variants. 

Severity: Early evidence has shown a likely decrease in severity, but the criteria for measurement are inconsistent. Reports from several countries in Southern Africa have shown sharp increases in case activity, that have declined more rapidly compared to previous waves. Data also indicate the risk of hospitalization is lower with Omicron in most cases. This data is mostly from countries with high levels of population immunity, so it is not clear how severe Omicron is in populations with lower vaccine coverage, or exposure to other variants. A report from the Imperial College London, from 22 December 2021, found a 41% reduced risk of hospitalization with Omicron compared to Delta.

Overall, “…[data] suggest a reduced risk of hospitalization for Omicron compared to Delta; and in the United Kingdom, a reduction in severity among hospitalized patients.

Vaccine Efficacy: The WHO has indicated in their FAQ that all vaccines currently listed by WHO may be effective against this variant. Large increases in case activity in countries with high vaccination rates is suggestive of immune escape, underscoring the need for vaccination, particularly booster vaccination. There is also limited evidence that natural immunity wanes as well.

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Variants of Interest

Lambda | C.37

First detected in Peru in August 2020.

Transmissibility: Some evidence has shown an increase of 64%, and that it is likely more infectious than the Gamma and Alpha variants.

Vaccine Efficacy: A study by the University of Chile found the CoronaVac vaccine was only 3% effective after the first dose, but increased to 56% after the second dose. Sinovac had a similar efficacy profile; 50.4% effective after the second dose. Pre-print evidence indicates that the mRNA vaccines such as Pfizer/BioNTech and Moderna have a slight reduction but remain effective.

Treatment Efficacy: Data are lacking, but preliminary evidence indicates that monoclonal antibody treatments remain effective.

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Mu | B.1.621

First detected in Colombia in January 2021.

Vaccine Efficacy: Several mutations suggest it could be more resistant to vaccines. Preliminary data shows Mu has reduced vaccine effectiveness similar to the Beta variant. More research is required

Treatment Efficacy: Data is lacking.

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WHO Variant page:

US CDC Variant page:

US CDC Variant tracker:

Medical Microbiology 4th edition – Chapter 43 Viral Genetics:

WHO: Enhancing Readiness for Omicron (B.1.1.529): Technical Brief and Priority Actions for Member States