Seasonal coronaviruses are a group of viruses that have circulated in human populations for many decades. These viruses are a common cause of mild to moderate respiratory illnesses, frequently presenting as the common cold.
Common Types and Associated Symptoms
Four main types of seasonal human coronaviruses are recognized: HCoV-229E, HCoV-NL63, HCoV-OC43, and HCoV-HKU1. These viruses cause symptoms that are indistinguishable from those of a common cold. Individuals might experience a runny nose, a sore throat, coughing, headaches, or sometimes a low-grade fever.
Infections from these seasonal coronaviruses are mild in most healthy individuals. However, in vulnerable populations, these viruses can lead to more serious lower respiratory tract illnesses. Infants, the elderly, and individuals with weakened immune systems may develop conditions such as pneumonia or bronchitis.
How Seasonal Coronaviruses Spread
Seasonal coronaviruses primarily spread through respiratory droplets released when an infected person coughs or sneezes. Transmission can also occur through contact with contaminated surfaces (fomites) if a person touches them and then their eyes, nose, or mouth.
Infections are most frequent during colder months, from fall through winter in temperate climates. This seasonal pattern is similar to influenza viruses, contributing to annual surges in respiratory illnesses. Immunity acquired after an infection can wane over time, allowing for reinfection and contributing to the persistent circulation of these viruses.
Comparing Seasonal and Novel Coronaviruses
Seasonal coronaviruses cause mild, upper respiratory tract illnesses that resolve without significant intervention. In contrast, novel coronaviruses, such as SARS-CoV-2 which causes COVID-19, often induce severe lower respiratory disease. These viruses can lead to conditions like pneumonia and frequently affect multiple organ systems beyond the respiratory tract.
The public health impact also differs significantly between these two categories. Seasonal coronaviruses are endemic, meaning they are consistently present within a population and cause predictable, manageable illness. Conversely, novel coronaviruses, particularly SARS-CoV-2, triggered a global pandemic due to their high transmissibility and a widespread lack of pre-existing population immunity. Earlier novel coronaviruses, like the original SARS-CoV and MERS-CoV, also demonstrated a capacity for severe disease and outbreaks, though not on the global scale of COVID-19.
A contributing factor to the difference in disease severity lies in their cellular targets within the respiratory tract. While both types of viruses infect respiratory cells, novel coronaviruses often target specific receptors, such as the ACE2 receptor, which are abundant in lower respiratory tract cells and other organs. This broad cellular tropism and the resulting widespread inflammation contribute to the more severe and systemic nature of diseases caused by novel coronaviruses compared to the localized, milder infections typical of seasonal variants.
Managing and Preventing Infection
There is no specific antiviral treatment for common cold coronaviruses, so management focuses on alleviating symptoms. This typically involves rest, maintaining adequate hydration, and using over-the-counter medications for pain or fever.
Prevention of seasonal coronavirus infections relies on standard hygiene practices that are effective against most respiratory viruses. Frequent hand washing is recommended, as is avoiding touching the eyes, nose, and mouth. Staying home when sick is also a crucial measure to prevent spreading the virus.