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.