This is a fast-moving area, and the information presented here should be read as correct at the time of publication. Other Library briefings, linked below, provide more detailed information about different aspects of the Covid-19 pandemic and the Government’s response.

How and why do new variants arise?

Covid-19 disease is caused by the severe acute respiratory syndrome coronavirus 2 virus, abbreviated to SARS-CoV-2.

When a virus replicates, mutations often occur while its genetic material is being copied. These often have no effect on the behaviour of the virus. Sometimes, however, these mutations result in changes which give this new version of the virus (usually called a strain or variant) distinct characteristics as compared to the original virus. These characteristics may change the way the virus behaves, such as making it more transmissible, causing more severe symptoms or meaning that treatments or vaccines are less effective.

A new variant might be identified as a ‘variant under investigation’ or a ‘variant of concern’. The UK Health Security Agency (UKHSA) defines these terms:

Variant under investigation (VUI): a variant with potentially concerning mutations which is also freely spreading through the community in the UK or other countries (known as community transmission)

  • Variant of concern (VOC): a variant that has significant characteristics, such as increased transmissibility, severity or ability to infect a person

The Covid-19 Genomics UK Consortium (COG-UK) carries out the sequencing of SARS-CoV-2 variants, in collaboration with UK public health agencies, academic institutions, the Wellcome Sanger Institute, Lighthouse Labs and NHS laboratories. The UK Health Security Agency’s New Variant Assessment Platform aims to support other countries strengthen their genomic sequencing capacity. This could be by building on existing infrastructure or sequencing and analysing samples in the UK if there is no in-country capability.

For a more detailed discussion about Covid-19 variants, see the Parliamentary Office of Science and Technology’s briefing, SARS-CoV-2 virus variants: a year into the COVID-19 pandemic.

The Omicron variant

In late November, there were reports of a new variant of SARS-CoV-2 called Omicron. The first specimens of this variant were collected in South Africa on 8 November and Botswana on 11 November. The first genomes (genetic codes) of the variant were uploaded to GISAID (a global platform for sharing genomic data on viruses) on 22 November.

South Africa reported its findings to the World Health Organization (WHO) on 24 November. By the end of November, South Africa had experienced a steep increase in infections, which coincided with the detection of the Omicron variant.

Following advice from a WHO sub-group, the Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE), the WHO designated Omicron a variant of concern on 26 November. The UK Health Security Agency (UKHSA) designated Omicron a VOC of 27 November.

What do we know about Omicron variant so far?

Much remains unknown about the Omicron variant. Research is ongoing and it’s likely that more information will be available in the coming days and weeks.

 The Omicron variant has many mutations which the WHO has described as “concerning”. The UK Health Security Agency (UKHSA) has said that, based on the location of the mutations in the viral genetic material and experience from other variants, these might change the behaviour of the Omicron variant. These mutations could affect its ability to evade the immune system, transmissibility and the effectiveness of some medicines used to treat Covid-19.

The Government has said that data suggests Omicron has a very high growth rate and is now spreading rapidly.

As of 22 December, UKHSA reported that there had been a total of 74,089 confirmed cases of the Omicron variant in the UK.

For a more detailed discussion about the scientific understanding of the Omicron variant, the Parliamentary Office of Science and Technology has the briefing, Covid-19: The Omicron Variant.

How is the Omicron variant detected?

Whole genome sequencing is used to analyse the entire genetic code of a variant. It is vital to identifying the type of variant present in a sample but takes a few days to process.

UKHSA has suggested that PCR testing could be used as an early indicator of the Omicron variant due to ‘S-gene target failure’. PCR testing for the virus involves testing for three different target genes. One of these is the S gene, which is not detected in PCR testing for Omicron and some other variants. The failure to detect the S gene in a Covid sample can therefore be an indication of the Omicron variant.

How has the UK Government responded to Omicron?

On 26 November, Health Secretary Sajid Javid gave a statement in Parliament about the newly identified variant. The Health Secretary said the new variant might pose a “substantial risk to public health” adding that early indications suggested it may be more transmissible than the Delta variant, and less susceptible to existing vaccines and anti-viral medication. He said the Government was working with international partners to learn more about the variant and encouraged people to take up the booster vaccine.

Dr Jenny Harries, Chief Executive of UKHSA, said that UKHSA would continue efforts to understand the effect of Omicron on transmissibility, severe disease, mortality, antibody response and vaccine efficacy.

On 8 December, the Prime Minister confirmed that England would move to ‘Plan B’ of its Autumn and Winter Plan.

Entry to nightclubs and high-capacity venues

People attending nightclubs and other high-capacity venues are now required to demonstrate that they have had two doses of the Covid-19 vaccine or proof of a negative test result in the previous 48 hours. This requirement came into effect on 15 December, with Parliament approving the regulations on 14 December 2021.

People can use the NHS Covid Pass to show that they meet the requirements.

For further information about the use of the Pass as a condition of entry to some venues, read our briefings:


On 29 November, the Joint Committee for Vaccines and Immunisation (JCVI) updated its advice on booster vaccinations. This widened eligibility from adults over 40 years to all those aged 18 and over. The JCVI also recommended a second dose of the Pfizer BioNTech vaccine for people aged 12 to 15 years, 12 weeks after the first dose.

The Government pledged that all eligible adults in England would be offered a booster vaccine by the end of December, and reduced the required period for the booster vaccine, following the first two doses, from six to three months.

For further information on vaccinations, read our Library briefings:


Following concerns about the Omicron variant, the UK Government introduced a range of travel measures.

As of 6 December, the Government had placed 11 African countries on the UK’s red travel list, which meant that people travelling back to the UK from these countries would be required to undertake quarantine in a Government approved facility.

The Government subsequently removed all 11 countries from the red list as of 15 December, explaining that the red list had become ‘less effective’ as Omicron cases rise in the UK and other countries.

The Government introduced new requirements for pre-departure testing and self-isolation for people travelling to the UK.

For further information about travel restrictions, read our briefing: Coronavirus: International Travel FAQs for England.

Self-isolation requirements for close contacts

Since 16 August 2021, individuals who have been fully vaccinated in the UK are not legally required to self-isolate where they have been identified as a close contact of someone who has tested positive for Covid-19. 

In response to concerns about the Omicron variant, the Government introduced changes to the regulations to mean that from 30 November 2021 anyone who was identified as a close contact of someone who was positive for Covid-19 and had (or was suspected of having) the Omicron variant would be required to self-isolate for the full period, irrespective of being vaccination status. However, a further change in the law on 14 December has removed this requirement.

The Government have said that, from 14 December, all fully vaccinated people who are notified that they are a close contact of someone who has covid-19 (whether it is the omicron variant or not) should undertake daily lateral flow testing for seven days. There is also strong advice for people who have been identified as a close contact to “limit close contact with other people outside their household, especially in crowded or enclosed spaces and with anyone who is more vulnerable.” More information on self-isolation requirements is provided in the Library briefing, Coronavirus: Self-isolation and Test and Trace Support Payments.

Face coverings

The Government re-introduced a requirement for face coverings to be worn in most indoor settings, with exemptions for all hospitality settings and some individuals who are unable to wear them. This came into effect on 30 November. Parliament approved the regulations on 14 December.

Support for businesses

On 21 December, the Government made a further announcement about support for businesses most affected by the Omicron variant. This included the reintroduction of the Statutory Sick Pay Rebate scheme. Further information about the Government’s support is available on the Library website.

Working from home

From 13 December, the Government has advised that people should work from home, where possible.

For further information about home working and associated issues, read our briefing: Coronavirus: Returning to work.

Further reading

House of Commons Library, Coronavirus variants and surge testing in England.

US Centers for Disease Control and Prevention, Omicron Variant: What you need to know

European Centre for Disease Prevention and Control, Weekly epidemiological update: Omicron variant of concern (VOC) – week 50 (data as of 19 December 2021)

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