Why everyone is sick right now - Today, Explained Recap

Podcast: Today, Explained

Published: 2026-01-11

Duration: 30 minutes

Guests: Caitlin Jetelina, Carl Zimmer, Ellen Foxman

Summary

The episode examines why flu cases are surging, focusing on viral mutations and the role of immunity. It discusses the benefits and limitations of vaccines and the potential for viruses to boost our immune systems.

What Happened

Flu cases in the U.S. have reached record levels, with 11 million cases and 5,000 deaths reported. Epidemiologist Caitlin Jetelina explains that cold weather and social gatherings accelerate virus spread, and the flu's mutations make it more virulent. This year's flu strain, H3N2, mutated over the summer, shifting to a K subclade, causing severe outbreaks in several countries.

Current vaccines may not fully protect against new flu strains, but they still prevent severe outcomes like hospitalization and death. Jetelina emphasizes the importance of getting the flu shot, even if late, as it can still offer protection against multiple circulating strains.

Besides the flu, other viruses like COVID-19, RSV, and norovirus are also prevalent. These viruses thrive in colder months and can cause serious illness, especially in vulnerable populations.

Carl Zimmer provides insights into viruses, describing them as simple genetic shells that invade cells to reproduce. He highlights how our immune responses, such as fever, are our body's way of fighting back, though they can also cause harm if uncontrolled.

Zimmer explains that viruses mutate frequently due to sloppy genetic replication, leading to diverse strains. Some mutations allow viruses to spread more effectively, making it challenging to develop universal vaccines.

Ellen Foxman discusses how innate immunity, a natural defense present from birth, can protect against viruses even without prior exposure. She notes that during the pandemic, measures like masking reduced virus circulation, impacting immunity, especially in children.

Foxman's research indicates that mild viral infections can stimulate innate immunity, offering protection against more severe viruses. She is exploring ways to enhance this natural defense to prevent illnesses like the flu.

Key Insights

• The current flu season in the U.S. has reached unprecedented levels with 11 million cases and 5,000 deaths, driven by the H3N2 strain that mutated into a more virulent K subclade over the summer.
• Flu vaccines, while not fully protective against new strains, still significantly reduce the risk of severe outcomes such as hospitalization and death, underscoring the value of vaccination even later in the season.
• Viruses like COVID-19, RSV, and norovirus are thriving in colder months, posing serious health risks, particularly to vulnerable populations, as they exploit the seasonal increase in indoor social interactions.
• Innate immunity, a defense mechanism present from birth, can be enhanced by mild viral infections, providing protection against more severe viruses, a potential avenue for improving public health resilience.