Spain hit by fast-spreading Nimbuses of COVID and Stratus

Spain has seen a gradual rise in COVID-19 as the two new Omicron variations, Nimbus NB.1.8.1 and Stratus XFG, begin to circulate.

Although public health experts emphasize that most infections remain mild – especially for those who are vaccinated – authorities closely monitor the situation to prevent local outbreaks.

What are Nimbuses and Stratus?

Nimbus

Nimbus was designated as a Variant under Monitoring (VUM). World Health Organisation (WHO). Identified in January 2025In some regions, by the end of April, Nimbus had spread rapidly throughout Asia and Europe. Experts describe Nimbus, a highly transmissible variation due to its ability of binding strongly to human ACE2 receptors. This may explain its rapid spreading.

The name “Nimbus”, which is a cloud, has nothing to do with pop culture. Researchers chose the name to differentiate the variant from other COVID-19 strains. According to Prof. T. Ryan Gregory who is part of a team tracking these variants Nimbus, has “established itself among hosts as a new virulent lineage capable of causing a wave in some regions.”

Stratus

Stratus is rapidly spreading in Europe, India, North America and South America. It is currently not listed by the WHO as a variant that is monitored. Stratus, unlike Nimbus has a greater ability to evade antibody, allowing it infect people who have partial immunity due to vaccination or previous infection. Researchers point out that although Stratus might not bind human cells as well as Nimbus does, its immune evasion abilities give it a competitive advantage in some populations.

Genetic Background

Both variants result from genetic recombination. This occurs when multiple Omicron lineages invade the same cell, and exchange genetic material. Nimbus has seven new mutations in the spike protein and other changes, which increase its ability to invade cells. Stratus contains spike mutations which may help the virus evade antibodies and increase the chances of reinfection.

Symptoms and signs of Nimbuses and Strata

Nimbus Symptoms (NB.1.8.1)

• The sensation of a razor blade in the throat is severe.
• Fatigue
• Cough
• Runny Nose
• Headache
• Mild fever or chills
• Hoarseness
• Gastrointestinal disorders such as nausea, diarrhoea, or vomiting

Stratus (XFG Symptoms

• Chronic dry cough
• Itchy or sore throat
• Hoarseness
• Fever or chills
• Fatigue
• Headache
• Nasal congestion or runny nasal
• Nausea, vomiting, or diarrhoea

Although symptoms are similar, Nimbus may cause more throat irritation and gastrointestinal problems, whereas Stratus can present as a persistent, dry cough. The majority of infections are mild. However, early detection, treatment, and isolation are essential to avoid complications and slow the spread.

Public Health Response

Surveillance and testing

Spanish health authorities increase genomic sequencing, and monitor hospital admissions for tracking these variants. Laboratories analyze samples to detect any changes in symptoms and transmissibility. Hospitals are being urged to notify regional health authorities immediately of any abnormal symptom patterns.

Vaccination & Prevention

COVID-19 remains effective, in particular updated boosters which protect against severe illnesses, hospitalisations and deaths. Dr. Alberto Martínez Martínez, a specialist in Cadiz, advises, “Vaccination continues to be the best defence. People with chronic conditions or older adults should seek medical care if they develop symptoms.

Guide for Visitors and Expats

Residents and visitors to Spain are advised to monitor symptoms, avoid close contact with those showing signs of illness, practice good hygiene, wear masks indoors, and be aware of the spread of disease. Expats must also have medical insurance or access to healthcare providers. They should also know where they can get tested, if needed.

Spain: Implications

COVID-19, although it does not pose a serious public health risk at this time, is evolving. Authorities emphasize that vaccination and adherence to safety measures are essential. To reduce confusion and reinforce prevention measures, public health messages are directed at residents as well as visitors.

Spain’s experience demonstrates the importance of ongoing surveillance and public education. By knowing the differences between Nimbus Stratus, recognising the symptoms, and remaining vaccinated expats and visitors can help protect the community.