The new NB.1.8.1 or Nimbus Covid-19 variant has rapidly increased Covid positive test rates in the UK by 97% over three months, prompting heightened surveillance and vaccination efforts amid concerns of wider spread but no rise in severity yet.
A new strain of Covid-19, known as NB.1.8.1 or the Nimbus variant, has been confirmed in the UK, where reported positive test rates have surged by 97% since early March. This variant has emerged in at least twelve cases across the country, leading the UK Health Security Agency (UKHSA) to acknowledge that Nimbus is becoming a “growing proportion” of global Covid-19 cases. As of June 1, 6.1% of tested individuals were found to be positive for the virus, a considerable increase from 3.21% just three months earlier. Dr Gayatri Amirthalingam, the deputy director of UKHSA, indicated that they are carefully monitoring this new variant, stating, “UKHSA is monitoring all available data relating to SARS-CoV-2 variants in the UK and abroad, and we continue to publish our findings in our regular Flu and Covid-19 surveillance reports.”
Nimbus is characterised as highly contagious, although health officials have yet to observe a corresponding rise in the severity of the illness it causes. This variant has sparked concerns not only in the UK but globally, with reports suggesting a significant uptick in its prevalence in other countries, particularly in regions like the Western Pacific. The World Health Organization (WHO) notes that Nimbus accounted for just over 10% of all global Covid-19 cases as of May. Despite its spread, officials from various health authorities assert that the public risk remains low, emphasising the importance of vaccinations, especially for vulnerable populations.
The rapid ascent of the Nimbus variant has drawn comparisons to previous waves driven by variants such as XBB.1.5, which showcased similar explosive growth patterns. According to surveillance data, the NB.1.8.1 strain has shown a remarkable trajectory in locations like Hong Kong, where it surged to nearly 100% prevalence in a matter of weeks. This kind of rapid propagation often precedes significant public health challenges, prompting experts to caution that newly emerging variants could potentially generate future waves of infections.
Health officials, both in the UK and internationally, advise that individuals testing positive or experiencing respiratory symptoms should limit contact with vulnerable individuals and remain at home when possible. The WHO has recommended that countries continue to perform neutralisation assays to assess vaccine efficacy against the new strain, as well as to monitor the severity of cases it causes. The safety and effectiveness of existing vaccines against Nimbus continue to be the subject of research, and discussions around updating vaccination strategies are underway.
Vaccination remains a critical tool in navigating this evolving landscape. The UK’s health agencies echo the WHO’s advice that immunisation efforts must persist, particularly as variants like Nimbus emerge. As public health authorities assess the impact of this strain, continuous monitoring will be essential to better understand its implications for global health and to ensure that appropriate precautions and responses can be instituted to protect communities.
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Source: Noah Wire Services
- https://www.express.co.uk/news/uk/2065663/uk-covid-nimbus-variant-spread – Please view link – unable to able to access data
- https://www.axios.com/local/seattle/2025/06/02/covid-subvariant-nb181-washington-cases – The article reports that over a dozen cases of the new COVID-19 subvariant NB.1.8.1 have been detected in Washington state, according to federal surveillance data. This variant, which emerged in the U.S. during March and April, has been gaining global attention. Fourteen cases have been genetically sequenced in Washington based on global tracking data. The World Health Organization has labeled NB.1.8.1 as a ‘variant under monitoring’ due to its rising prevalence globally. Despite the increase in presence, health officials report that the public risk remains low, with no evidence suggesting a rise in the severity of illness associated with this subvariant. ([axios.com](https://www.axios.com/local/seattle/2025/06/02/covid-subvariant-nb181-washington-cases?utm_source=openai))
- https://www.huffingtonpost.es/life/salud/la-oms-advierte-sobre-nueva-variante-covidnb181.html – The article discusses the World Health Organization’s warning about the new SARS-CoV-2 variant NB.1.8.1, which has shown an increase in its global prevalence. Although this variant currently accounts for just over 10% of all global cases, it remains lower compared to others like LP.8.1. Its rapid expansion has led to its inclusion under monitoring. Derived from the recombinant variant XDV.1.5.1 and first detected in January 2025, NB.1.8.1 exhibits limited immune evasion against existing vaccines, which are expected to remain effective. Most cases have been reported in the Western Pacific Region, with no increased severity in clinical presentations. The WHO recommends countries conduct neutralization assays and continue monitoring severity indicators and vaccine efficacy. ([huffingtonpost.es](https://www.huffingtonpost.es/life/salud/la-oms-advierte-sobre-nueva-variante-covidnb181.html?utm_source=openai))
- https://time.com/7289133/new-covid-variant-nb-181/ – The article provides an overview of the new COVID-19 variant NB.1.8.1, which has emerged as the dominant strain in China, leading to increased hospitalizations and emergency room visits. Initially detected in April in travellers from multiple countries, including China, Japan, and Spain, it has now been identified in a few U.S. states through CDC testing at airports. Although cases in the U.S. remain sparse, public health officials and the WHO are monitoring the variant closely. NB.1.8.1 belongs to the Omicron family, suggesting that existing vaccines still offer protection against severe disease. Discussions are ongoing at the FDA about updating vaccines, but so far, the agency has recommended continuing with a JN.1-targeted vaccine. Experimental vaccines from Pfizer and Moderna targeting a related strain (LP.8.1) show promise. NB.1.8.1 manifests with symptoms similar to other COVID-19 strains, such as sore throat, fever, and fatigue, but its enhanced ability to infect cells may increase transmissibility. While vaccination remains important, particularly for vulnerable groups, recent policy shifts by U.S. health authorities could limit access and coverage for the general population, including healthy children and adults, until more safety data become available. ([time.com](https://time.com/7289133/new-covid-variant-nb-181/?utm_source=openai))
- https://www.thailandmedical.news/news/nb-1-8-1-the-new-sars-cov-2-variant-racing-to-dominate-is-a-new-wave-coming – The article discusses the rapid rise of the SARS-CoV-2 variant NB.1.8.1, which has shown explosive growth, climbing from 0% to nearly 100% prevalence in Hong Kong within two months. This rapid ascent mirrors the trajectory of previous wave-driving variants like XBB.1.5 and JN.1. By April 14, 2025, NB.1.8.1 was still accelerating at a 120% weekly growth rate, a speed only seen in major variants that triggered global surges. Beyond Hong Kong, NB.1.8.1 is gaining traction in Singapore, rising from 7% to 8.5% in one week by April 14, 2025, though its growth there is slower. This variant’s ability to outpace competitors raises alarms, especially as it follows a pattern seen in Hong Kong’s 2022 Omicron BA.2 wave, which led to one of the highest per-capita death rates globally due to low natural immunity and vaccine hesitancy in vulnerable groups. The article highlights NB.1.8.1’s unique genetic profile, including mutations like S:K478I and A435S, which enhance transmissibility. The rapid growth and transmissibility of NB.1.8.1 suggest it could signal a new wave, especially in regions with waning immunity. Experts are watching closely, with some calling for updated vaccines to target its unique spike profile. ([thailandmedical.news](https://www.thailandmedical.news/news/nb-1-8-1-the-new-sars-cov-2-variant-racing-to-dominate-is-a-new-wave-coming?utm_source=openai))
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https://www.lbc.co.uk/news/new-covid-variant-strain-where-is-the-new-strain-uk-where-did-it-come-from/ – The article provides a comprehensive list of locations in the UK where the new COVID-19 variant NB.1.8.1 has been identified. These areas include:
– Glasgow and surrounding areas such as Linwood, Newton Mearns, Airdrie, Bonhill, and Lenzie.
– Rural Northumberland near Rothbury.
– Newcastle-upon-Tyne and Gateshead, near Low Fell.
– Bishop Auckland in County Durham.
– Near Penrith in Cumbria.
– Middlesbrough.
– Hurst Green in Lancashire.
– Cleckheaton.
– Pocklington, near Hull.
– Two areas in the north of Merseyside, near Crosby and Kirkby.
– Central Manchester.
– Near Maltby in South Yorkshire.
– Wrexham and Burton, Cheshire.
– Near Matlock in Staffordshire.
– Eakring in Nottinghamshire.
– Woodhall Spa in Lincolnshire.
– Near Stafford in Staffordshire.
– Leicester area.
– Upper Hambleton, near Oakham.
– Dereham near Norwich.
– Stowmarket near Ipswich.
– Willingham in Cambridgeshire.
– Kettering.
– Kenilworth near Coventry.
– Oldbury area of Birmingham.
– Worcester.
– Hereford.
– Fishguard, Neath, Bridgend, Barry, and Newport.
– Bristol.
– Bridgwater and Exeter.
– Dorchester on the south coast.
– Newbury near Thatcham.
– New Alresford, near Winchester.
– Billingshurst.
– Dorking.
– Hailsham.
– Canterbury.
– London.
– Oxford.
– Welwyn Garden City near St Albans.
– Braintree.
– Stagsden near Bedford.
The article highlights the widespread presence of the new variant across various regions in the UK. ([lbc.co.uk](https://www.lbc.co.uk/news/new-covid-variant-strain-where-is-the-new-strain-uk-where-did-it-come-from/?utm_source=openai))
Noah Fact Check Pro
The draft above was created using the information available at the time the story first
emerged. We’ve since applied our fact-checking process to the final narrative, based on the criteria listed
below. The results are intended to help you assess the credibility of the piece and highlight any areas that may
warrant further investigation.
Freshness check
Score:
8
Notes:
The report introduces the NB.1.8.1 variant, also known as Nimbus, which has been identified in the UK. The earliest known publication date of similar content is June 4, 2025, in El País, reporting on the global increase of this variant. ([elpais.com](https://elpais.com/sociedad/2025-06-04/claves-una-nueva-variante-de-covid-eleva-los-contagios-aunque-la-oms-considera-bajo-el-riesgo-para-la-poblacion.html?utm_source=openai)) The Express article provides more detailed information specific to the UK context, including quotes from Dr. Gayatri Amirthalingam of UKHSA. The presence of a press release from UKHSA indicates a high freshness score, as press releases are typically recent and authoritative. However, the Express article includes updated data but recycles older material, which may justify a higher freshness score but should still be flagged. Additionally, the report includes references to other sources, suggesting a synthesis of information rather than original reporting. ([elpais.com](https://elpais.com/sociedad/2025-06-04/claves-una-nueva-variante-de-covid-eleva-los-contagios-aunque-la-oms-considera-bajo-el-riesgo-para-la-poblacion.html?utm_source=openai), [huffingtonpost.es](https://www.huffingtonpost.es/life/salud/la-oms-advierte-sobre-nueva-variante-covidnb181.html?utm_source=openai))
Quotes check
Score:
7
Notes:
The report includes a direct quote from Dr. Gayatri Amirthalingam, deputy director of UKHSA: “UKHSA is monitoring all available data relating to SARS-CoV-2 variants in the UK and abroad, and we continue to publish our findings in our regular Flu and Covid-19 surveillance reports.” A search for this exact quote reveals no earlier usage, suggesting it may be original or exclusive content. However, the presence of similar information in other sources raises questions about the originality of the content. ([elpais.com](https://elpais.com/sociedad/2025-06-04/claves-una-nueva-variante-de-covid-eleva-los-contagios-aunque-la-oms-considera-bajo-el-riesgo-para-la-poblacion.html?utm_source=openai), [huffingtonpost.es](https://www.huffingtonpost.es/life/salud/la-oms-advierte-sobre-nueva-variante-covidnb181.html?utm_source=openai))
Source reliability
Score:
6
Notes:
The narrative originates from the Express, a UK-based tabloid newspaper. While it is a well-known publication, its reputation for accuracy and reliability is often questioned. The Express has a history of sensationalism and has been criticised for publishing unverified or misleading information. Therefore, the reliability of the source is moderate, and the uncertainty is flagged.
Plausability check
Score:
8
Notes:
The report’s claims about the emergence of the NB.1.8.1 variant, also known as Nimbus, are plausible and align with information from other reputable sources. The World Health Organization (WHO) has acknowledged the presence of this variant and its global spread. ([elpais.com](https://elpais.com/sociedad/2025-06-04/claves-una-nueva-variante-de-covid-eleva-los-contagios-aunque-la-oms-considera-bajo-el-riesgo-para-la-poblacion.html?utm_source=openai)) The report’s emphasis on the variant’s transmissibility and the monitoring efforts by UKHSA is consistent with current public health responses. However, the lack of supporting detail from other reputable outlets and the sensational tone of the Express raise concerns about the report’s overall credibility.
Overall assessment
Verdict (FAIL, OPEN, PASS): FAIL
Confidence (LOW, MEDIUM, HIGH): MEDIUM
Summary:
The report introduces the NB.1.8.1 variant, also known as Nimbus, in the UK context. While the information aligns with reports from other sources, the Express’s history of sensationalism and the lack of supporting detail from other reputable outlets raise concerns about the report’s credibility. The moderate reliability of the source and the potential recycling of content further diminish confidence in the report’s accuracy.
