How Cold Weather Affects COVID-19

There was an uptick in COVID-19 cases in the winters after the initial pandemic surge in 2020. Like last winter, this winter is seeing a surge in post-holiday cases.


Staying Inside – Post-Holiday COVID-19

The holidays are a time when people get together. In colder parts of the country, the gatherings are often indoors. The closeness of people and lack of ventilation can put people at risk of contracting COVID-19. But that’s only a part of why there is a COVID-19 surge after the holidays.

The cold weather does play a part in the increase in COVID-19 cases. Ran Xu, an assistant professor at the University of Connecticut, co-authored a study showing the correlation between cold weather and the rate of COVID-19 cases. Dr. Xu says he discovered biological evidence that COVID-19 is more active during the colder months. During these months, the combination of cold weather and high ultraviolet (UV) radiation can spike the rate of COVID-19 cases.

Humidity Levels

Another factor in the increased level of COVID-19 during the winter months is the decrease in humidity. Colder weather affects the nose. People’s noses dry up, impairing the function of the cilia, the tiny hairs in the nose. The decreased function means the cilia may fail to remove a virus from the nose.

Approximately 87% of Americans spend their time indoors during the winter when indoor humidity levels are about 10-40%. Researchers believe the optimal humidity level to decrease the risk of COVID-19 transmission is between 40-60%.  The increased time spent indoors and the decreased humidity are ideal for transmitting COVID-19.

Winter Surge

Because coronavirus surveillance data was scaled back when the public health emergency ended in May 2023, it’s hard to tell the number of cases that have occurred or are occurring. As a result, the Centers for Disease Control and Prevention (CDC) is cautiously discussing the winter surge in cases.

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Wastewater Tracking

The CDC tracks reported cases of COVID-19 and wastewater to determine COVID-19 rates. Sewers can track asymptomatic and mild cases that health officials may not record. The information gathered by the CDC shows that the country is experiencing higher COVID-19 cases than last winter. Wastewater data is also helpful to hospitals because an increase in rates allows hospitals to plan for an increase in nurses and beds.

CDC experts caution that the levels of coronavirus discovered in sewage should be looked at as how the virus is trending, not the actual cases.

The CDC isn’t the only organization tracking the rates of coronavirus in wastewater. Biobot Analytics and WasterwaterSCAN are also reporting more COVID-19 cases than last year.

Hospital Reporting

The COVID-19 public health emergency ended in May 2023. The end of the public health emergency meant hospitals no longer had to report suspected COVID-19 cases. They are, however, still required to register confirmed cases. The CDC uses the number of reports to determine the rate of COVID-19 transmission. Using this information, the CDC found approximately 35,000 people were hospitalized during the week of December 30, 2023. The number of hospitalizations during the same week in 2022 was 44,000. However, because the public health emergency ended in May 2023, it is unknown if the number of hospitalizations due to COVID-19 is higher.


The surge in COVID-19 cases serves as a reminder that COVID-19 can impact people’s health. People can take specific preventative measures to decrease or prevent the risk of becoming ill. Talk to your medical professional about masks, vaccines, and booster shots. Together, you can determine the best option to protect yourself from COVID-19 or its severe symptoms.

Christina Sisti, DPS, MPH, MS, is a bioethicist and health care policy advocate. She works to create awareness and improve healthcare policy for those with long-term health issues.

About the Author - Reeve Staff

This blog was written by the Reeve Foundation for educational purposes. For more information please reach out to

Reeve Staff

The opinions expressed in these blogs are the author's own and do not necessarily reflect the views of the Christopher & Dana Reeve Foundation.

This publication was supported by the Administration for Community Living (ACL), U.S. Department of Health and Human Services (HHS), as part of a financial assistance award totaling $160,000 with 100% funding by ACL/HHS. The contents are those of the author(s) and do not necessarily represent the official views of, nor an endorsement by, ACL/HHS or the U.S. government.