COVID-19 cases are rising in the US; Why does COVID spike in the summer and how to stay safe

Time of India

23-07-2025

As summer heats up, so are COVID-19 cases. The proof lies in the data of rising infections in about 25 states in the United States of America, including hotspots like California, Florida, and Texas, signaling the onset of a 'summer wave', confirmed by CDC wastewater data and surveillance systems.
Though typically associated with winter peaks, COVID-19 has grown into a biannual pattern. After months of low transmission, the Centers for Disease Control and Prevention (CDC) notes that COVID is resurging due to fading immunity and the emergence of new variants, notably NB.1.8.1 – the Nimbus strain.
Historically, summer spikes follow holiday travel, indoor retreat during heat waves, and increased social gatherings.
These increases stem from waning immunity, new variants (like NB.1.8.1, XFG, KP.3.1.1), and human behaviors such as indoor air conditioning and travel. While vaccines and treatments have greatly lowered severe outcomes, this renewed surge calls for the need for layered protection.
COVID-19: Summer wave
As the CDC reports, rising infections are occurring in about half of the states in the United States of America, with 25 showing clear increases, particularly in Florida, Texas, and California, which is linked to declining immunity and fresh variants like NB.1.8.1 (Nimbus) and XFG.
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Now, NB.1.8.1 – the Nimbus strain – is a dominant strain across 24–25 states. This strain, known for sore throat ('razor‑blade throat'), was first detected in March 2025. This particular strain has become the prevailing strain nationwide, known for its high transmissibility and causing sore and painful throats. However, the strain isn't linked to more severe illness.
On the other hand, XFG and LP.8.1, the other Omicron descendant variants are currently present at notable levels in wastewater samples.
Moreover, there's a twice-yearly seasonality pattern to note. Following emerging trends, COVID‑19 is settling into a biannual cycle, peaking in summer and winter. Experts deduce, this likely results from viral evolution and immunity decay. Similar patterns have been observed since 2020, driven by a mix of behavioral changes and viral adaptation.
Additionally, summer heat leads people indoors, where air conditioning tends to reduce ventilation and raise transmission risk.
Topping that, post-holiday travel and gatherings, especially around July 4, have historically fueled seasonal spikes. All of which explains the steep surge in infections.
Why the summer surge:
People's protection from vaccines and prior infections significantly declines by mid-to-late summer. New variants, like NB.1.8.1 ('Nimbus'), XFG, and KP.3.1.1, are more transmissible and can partially escape existing immunity.
Indoor exposure in air-conditioned spaces:
In hot regions, like mid-summer in the US, people spend more time indoors with closed windows and AC, limiting ventilation and increasing airborne virus risk.
Temperature and humidity effects:
Dry indoor air encourages aerosol formation, keeping virus particles aloft longer. Although high outdoor heat and humidity can reduce spread, air-conditioned indoor spaces recreate dry conditions that allow the virus to linger in aerosols.
Behavioral patterns and gatherings:
Summer activities, like travel, barbecues, concerts, and holiday celebrations, bring people together indoors and unwittingly amplify exposure.
CDC reports COVID activity is rising in over 25 states, including the Southeast and West Coast.
California wastewater shows a jump from very low to medium alert levels; 95% of sites detected SARS-CoV‑2. Though hospitalizations and deaths are lower than in past peaks, emergency visits for young children are notably increasing.
How to stay safe:
Although infections are rapidly surging across US states, the summer wave of COVID-19 has mostly mild to moderate symptoms.
Hospitalizations and deaths remain lower compared to earlier pandemic peaks. However, people who are aged 65+, immunocompromised, pregnant, or with chronic illness continue to face elevated risk.
Moreover, long COVID, which is an ongoing concern due to post-infection repercussions, such as fatigue and brain fog, is still reported, even after mild illness.
Here are some tips on staying safe.
Vaccination and boosting:
Updated boosters are recommended, especially for older, immunocompromised, or those whose last dose was >6 months ago.
Fall 2025 boosters matching recent variants will likely be available. It's advisable not to delay current doses while waiting.
Masks in high-risk settings:
Mask is a must. ALWAYS advocate for using masks (N95/KN95) indoors when crowded or poorly ventilated, such as transit, airports, and events. Healthcare workers, caregivers, and those in contact with high-risk people must continue using masks.
Testing and isolation:
Keep rapid antigen tests at home.
Test when symptoms emerge or after exposures. If positive, isolate for at least 5 days, and consider masking on days 6–10.
Ventilation and outdoor options:
Use fans, open windows, and HEPA filters to improve air circulation indoors. Opt for outdoor dining, events, or gatherings whenever feasible – instead of being cooped up indoors.
Hygiene and symptom vigilance:
Finally, go back to basics. Wash your hands frequently or use sanitizer. Avoid touching your face after contact with shared surfaces. Be alert to key symptoms, especially sore throat, fever, and fatigue, and act quickly.
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