New COVID-19 Infections "Increase for 7 Consecutive Weeks" — The Variant "Nimbus (NB.1.8.1)" Currently Spreading is Characterized by "Razor-like Throat Pain"

1. What is Happening in Japan Now —— "7 Consecutive Weeks of Increase"

According to the weekly report from the Ministry of Health, Labour and Welfare, the reported number of new COVID-19 cases per sentinel in Week 31 of 2025 (July 28 - August 3) was 5.53 people. This is an increase from the previous week's 4.12 people, marking a 7 consecutive weeks of increase. By prefecture, Miyazaki, Okinawa, and Kagoshima are at high levels (preliminary figures). Due to the revision of surveillance since April, careful interpretation of the data is necessary, but the nationwide upward trend is clear. Ministry of Health, Labour and Welfare

Note: In the update from August 9 to 15, the expression "8 consecutive weeks" also appeared. The terms "7 weeks" and "8 weeks" are mixed depending on the timing of the report. This article is based on the report from August 14, focusing on "7 consecutive weeks," while also introducing the latest trends. Tsuginodai

2. What is "Nimbus (NB.1.8.1)"?

Nimbus is a sub-lineage NB.1.8.1 of the Omicron JN.1 lineage. The WHO designated it as a VUM (Variant Under Monitoring) on May 23, 2025, organizing additional spike mutations (e.g., T22N, F59S, G184S, A435S, V445H, T478I, etc.). The name "Nimbus" is a nickname used by researchers and the citizen science community, with the official lineage name being NB.1.8.1. WHO CDNGavi

Globally, it has increased its share in Asia and the United States towards early summer 2025, becoming a factor in the **“summer wave”** in some regions. Northeastern Global NewsHuron Daily Tribune

3. Why Does it Affect the "Throat"? —— The Background of "Razor Blade Throat"

In domestic TV reports, "severe throat pain" is highlighted as a symbolic symptom of Nimbus. In English-speaking regions, the expression **“razor blade throat”** is also widespread. Due to the strong upper respiratory tract orientation of the Omicron lineage, complaints of hoarseness, pharyngitis, and swallowing pain are prominent. However, it does not appear in all cases, and nasal discharge, fever, headache, fatigue, and digestive symptoms may also occur concurrently. TBS NEWS DIGNortheastern Global NewsKQED

Note: The XFG (commonly known as Stratus), which emerged around the same time, is also reported to be associated with upper respiratory symptoms (hoarseness, pharyngeal discomfort), with dominant strains varying by region. In clinical settings, it is important to note that clinical symptoms alone cannot determine the strain. KQED

4. Known Severity and Reinfection Risk

As of now, public reviews and expert comments indicate that there is no definitive evidence that Nimbus is more likely to cause severe illness than existing strains. However, as transmissibility increases, the absolute number of infections rises, potentially increasing hospitalizations and deaths among the elderly and those with underlying conditions. Due to individual differences, **"many mild cases ≠ safe to be complacent"**. Northeastern Global NewsKera News

5. Why Did It Increase in "Summer"?

• Human Flow and Events: Increased opportunities for contact during Obon homecoming, summer festivals, and fireworks displays.

• Indoor Preference: Due to extreme heat, people tend to gather indoors where ventilation is insufficient.

• Immune Decline: Time has passed since the last vaccination or infection, causing waning immunity.

• Viral Adaptation: Since Omicron, there is a tendency for the virus to replicate easily in the upper respiratory tract even under high temperature and humidity.
  These factors combined have led to repeated summer waves in Japan as well. Ministry of Health, Labour and Welfare

6. Interpreting Japan's Latest Data (Week 31, Preliminary)

• National Average: 5.53 people per sentinel (previous week 4.12).

• Regional Differences: Miyazaki, Okinawa, Kagoshima are at high levels.

• Age Group: Increasing trend across all age groups.

• Points to Note: Due to the April 2025 reorganization of surveillance, the number of sentinels has changed. Year-on-year comparisons require caution. Check the trends by prefecture in the Ministry of Health, Labour and Welfare materials and cross-reference with municipal publications. Ministry of Health, Labour and Welfare

• When Unsure if It's Just a "Summer Cold"

  • Severe throat pain + fever / cough / fatigue / hoarseness → take an antigen test promptly.
    
    

• Testing Timing

  • The onset to positivity after exposure is trending shorter. If symptoms appear, test immediately, and even if negative, retest after 24–48 hours is advisable. KQED
    
    

• Signs to Seek Medical Attention

  • Difficulty in fluid intake, shortness of breath, persistent high fever, severe swallowing pain (unable to stop drooling or swallow), worsening in high-risk individuals → seek medical attention. Ministry of Health, Labour and Welfare

8. Home Care and Symptomatic Treatment (When Throat Pain is Severe)

• Antipyretics and Analgesics: Acetaminophen/Ibuprofen (check with a doctor or pharmacist for any medical history or concurrent medications).

• Moisturizing: Maintain humidity, use cold drinks and ice or warm honey water to keep the throat moist.

• Lifestyle: No smoking, rest##HTML_TAG_