BACK

What does colder weather mean for the spread of COVID-19?

This article was published on
May 12, 2021

This explainer is more than 90 days old. Some of the information might be out of date or no longer relevant. Browse our homepage for up to date content or request information about a specific topic from our team of scientists.

We do not know how the COVID-19 virus will impact people during colder winter months, but many experts predict higher rates of transmission and mortality than during the warmer, summer months. This is likely due to the impact cold weather has on human behavior such as forcing people inside where higher temperatures are preferred and ventilation is not sufficient to combat the spread of the virus. With groups of people congregating in confined spaces with limited airflow, the virus is able to circulate easily through aerosolized particles and respiratory droplets. Additionally, since a large percentage of COVID-19 have asymptomatic infections but they are still able to transmit the virus, many infected people are likely not restricting their movements to one quarantined room or area or taking necessary distancing or masking protocols. Traditionally, viruses like influenza and the common cold tend to increase amounts of infections in the winter and decrease in the summer. As with these other respiratory viruses, COVID-19 transmission will be impacted dramatically by control and prevention measures like social distancing, masking, and vaccination. The more people who engage in these activities, the more likely infections can be prevented. Though some viruses do not like humid, hot conditions, COVID-19 has been shown to spread rapidly in some regions during warm spring and summer months in both hemispheres. A study from October 13, 2020, before widespread prevention measures were undertaken showed that infections increased more quickly in places with less UV light and suggested that without any interventions, case rates may be highest in the winter and lower in the summer. However, weather itself does not appear to have an impact on the ability of the virus to spread though colder weather may make it more difficult for the body to fight respiratory infections. At this point, it is unknown whether or not COVID-19 will become a seasonal virus like influenza but we should expect any event that brings together people in closed environment can lead to an increased spread of the virus.

We do not know how the COVID-19 virus will impact people during colder winter months, but many experts predict higher rates of transmission and mortality than during the warmer, summer months. This is likely due to the impact cold weather has on human behavior such as forcing people inside where higher temperatures are preferred and ventilation is not sufficient to combat the spread of the virus. With groups of people congregating in confined spaces with limited airflow, the virus is able to circulate easily through aerosolized particles and respiratory droplets. Additionally, since a large percentage of COVID-19 have asymptomatic infections but they are still able to transmit the virus, many infected people are likely not restricting their movements to one quarantined room or area or taking necessary distancing or masking protocols. Traditionally, viruses like influenza and the common cold tend to increase amounts of infections in the winter and decrease in the summer. As with these other respiratory viruses, COVID-19 transmission will be impacted dramatically by control and prevention measures like social distancing, masking, and vaccination. The more people who engage in these activities, the more likely infections can be prevented. Though some viruses do not like humid, hot conditions, COVID-19 has been shown to spread rapidly in some regions during warm spring and summer months in both hemispheres. A study from October 13, 2020, before widespread prevention measures were undertaken showed that infections increased more quickly in places with less UV light and suggested that without any interventions, case rates may be highest in the winter and lower in the summer. However, weather itself does not appear to have an impact on the ability of the virus to spread though colder weather may make it more difficult for the body to fight respiratory infections. At this point, it is unknown whether or not COVID-19 will become a seasonal virus like influenza but we should expect any event that brings together people in closed environment can lead to an increased spread of the virus.

Publication

What our experts say

Many experts predict higher rates of transmission and mortality in colder seasons. This is likely due to the impact cold weather has on human behavior, such as forcing people inside where higher temperatures are preferred and ventilation is not sufficient to combat the spread of the virus. With groups of people congregating in confined spaces with limited airflow, the virus is able to circulate more easily.

Viruses like influenza and the common cold tend to increase amounts of infections in the winter and decrease in the summer. As with these other respiratory viruses, COVID-19 transmission will be impacted dramatically by control and prevention measures like social distancing, masking, and vaccination. The more people who engage in these activities, the more likely infections can be prevented.

Though some viruses do not like humid, hot conditions, COVID-19 has been shown to spread rapidly in some regions during warm spring and summer months in both hemispheres. A study from October 13, 2020, before widespread prevention measures were undertaken, showed that infections increased more quickly in places with less UV light. The study suggested that without any interventions, case rates may be highest in the winter and lower in the summer. However, weather itself does not appear to have an impact on the ability of the virus to spread. Colder weather may make it more difficult for the body to fight respiratory infections.

At this point, it is unknown whether or not COVID-19 will become a seasonal virus like influenza but we should expect any event that brings together people in closed environment can lead to an increased spread of the virus.

Context and background

The SARS-CoV-2 virus is known to be transmissible in all climates and it cannot be called "seasonal" at this point. Some lab experiments also showed that SARS-CoV-2 may be sensitive to temperature, humidity, and ultraviolet light. This leads people to believe that climatic effects could protect people from transmission. However, while experimental evidence can show environmental sensitivity, on a larger scale in the real world the effects of climate on COVID-19 appear to be negligible.

Resources

  1. Transmission Dynamics of Coronavirus Disease 2019 (COVID-19) in the World: The Roles of Intervention and Seasonality (medRxiv)
  2. How will COVID-19 affect the coming flu season? Scientists struggle for clues (Science)
  3. Misconceptions about weather and seasonality must not misguide COVID-19 response (Nature)
  4. Will the spread of covid-19 be affected by changing seasons? (NewScientist)
  5. Is COVID-19 a seasonal disease? (WEF)
  6. Hot or cold, weather alone has no significant effect on COVID-19 spread (SD)
  7. Why cold weather makes it harder for the body to fight respiratory infections (NatGeo)
  8. Why COVID outbreaks look set to worsen this winter (Nature)

Media briefing

Media Release

Expert Comments: 

No items found.

Q&A

No items found.