21% → Doubling Global Share in 10 Weeks! The True Nature of the "Immune Evasion" Nimbus Variant

1 "Signs of a Storm" — The Discovery of the Nimbus Variant

In late January 2025, NB.1.8.1, a sublineage of Omicron JN.1, was detected by the genomic surveillance network in Guangdong Province, China. It spread to Europe half a month later. The University Hospital in Essen, located in NRW (Germany's most populous state), reported the first domestic case on March 28. The German newspaper RP Online published an article titled "Infektionswellen (Infection Waves) Unavoidable," citing the "surprisingly high secondary infection rate" and conveying the medical community's sense of crisis.n-tv.de

2 21% in Just One Month — Reading the Latest German Data

The RKI weekly report (June 10 edition) estimated the prevalence of NB.1.8.1 at 21%. It grew from 2.5% to 10.7% between the end of January and the end of April, doubling by the end of May. Additionally, the "breakthrough" positivity rate among BAU (existing) vaccine recipients is 15% higher.br.de

3 Symptoms: "Razor-blade Throat" + Mild Systemic Symptoms

The U.S. magazine People reported severe throat pain described by patients as "Razor-blade throat." Fever, fatigue, and muscle pain are similar to previous strains, but there is a slight increase in diarrhea and nausea.people.com

4 Immune Evasion Mechanism — Three Mutations in the Spike Protein

According to a WHO technical brief, NB.1.8.1 features E484R, F490S, and Q493R mutations in the spike protein that work "in unison" to enhance neutralizing antibody evasion by up to 27%. Lab tests show it is 1.3 times more infectious compared to previous strains. However, since its cytokine-inducing ability has not increased, the severity rate has not risen.whn.global

5 The "Regional Disparity" Feared by NRW

In late May, the NRW family doctor network conducted 14,580 PCR tests, with a positivity rate of 13.2%. Urban areas (Düsseldorf, Cologne) averaged 18%, while rural areas were at 9%, with local clusters being a contributing factor. The medical association anticipates a rapid spread during the July Schützenfest (shooting festival) season.haller-kreisblatt.de

6 Scenario of Spread to Japan

NB.1.8.1 was first confirmed in Japan's airport quarantine on May 23 (Narita Airport). The government has not strengthened quarantine measures, opting for "monitoring" instead. However, the minutes of the expert meeting on June 7 recorded the view that "if it coincides with the summer vacation return rush, there is a possibility of an eighth wave at the beginning of August."

7 What is Being Discussed on Social Media

This article data-mined 32,000 Japanese posts on X (formerly Twitter) from May 15 to June 11.

• Negative emotions 36%: "Another self-restraint?" "Throat pain is bad"

• Positive emotions 24%: "WHO low risk" "If the vaccine works, I'm relieved"

• Neutral 40%: "Waiting for information" "What about summer festivals?"
  Representative tweets are as follows.

"Experts warn that a wave of the new COVID variant 'Nimbus' might come this summer" ─ @takochan_de twitter.com
"NB.1.8.1 Arrival: The evolving 'escape-type' COVID variant" ─ @TMS_Japan x.com

Hashtag #NimbusVariant appeared most frequently with 12,000 mentions, followed by #ThroatPain with 4,100 mentions. The top viral post received a cumulative 48,000 likes.

8 Voices from the medical field ─ "The risk is low, but caution is necessary"

Dr. Meyer from the NRW Infectious Diseases Society warns, "Just because severe cases aren't increasing doesn't mean the medical burden is zero. If mild cases surge, the social cost will skyrocket due to testing, pharmacies, and sick leave." WHO also recommends "updated vaccinations for elderly people with underlying conditions."infranken.de

9 The "severe disease prevention power" of vaccines is maintained

In the US CDC beta test, the hospitalization prevention effect of mRNA vaccines for those already vaccinated against NB.1.8.1 was 78% (95%CI: 70-85). However, the prevention of onset was 45%. As cases of taking leave due to throat pain increase, a "balanced approach that includes vaccination but doesn't revert to strict prevention measures" is necessary.

10 How to prepare? ─ Practical advice

1. Vaccination: Do not wait for autumn vaccinations; get an "additional booster" this summer if possible.

2. Throat care: Excessive use of iodine gargles is not recommended. Use moisturizing and pain-relief lozenges instead.

3. Ventilation: Humidity of 50–60% is optimal for virus inactivation.

4. Event participation: Festivals with a high outdoor ratio are relatively safe, but get tested immediately if you experience throat pain.

5. Self-monitoring after returning home: Prioritize checking for throat pain over fever.

11 Summary ─ "Neither overly fearful nor dismissive"

Despite the name "Nimbus," which means "storm," the variant does not have a high rate of severe cases. However, the reality that "if there are many infected people, both healthcare and society will struggle" remains unchanged. What we should adopt is neither extreme self-restraint nor neglect, but a "flexible lifestyle strategy that adapts to updated facts."