COVID-19, caused by the SARS-CoV-2 virus, has presented significant challenges to global public health. A recurring question for individuals and communities centers on how long someone remains contagious after infection. Understanding the duration of contagiousness is important for preventing further transmission and guiding isolation practices, helping people make informed decisions about returning to daily activities.
Typical Contagious Period
Individuals infected with COVID-19 can begin shedding the virus approximately two to three days before symptoms appear, making them contagious even before feeling sick. Viral shedding peaks around symptom onset or shortly thereafter. Most people with mild to moderate COVID-19 are most contagious during the first five to seven days following infection. The period of infectiousness can extend up to ten days after symptom onset for individuals with mild to moderate illness. While viral fragments can be detected for weeks or even months, this does not necessarily indicate ongoing contagiousness.
Factors Influencing Contagion Length
Several factors can influence how long an individual remains contagious with COVID-19. The severity of symptoms plays a role, with people experiencing severe illness, including those who are immunocompromised, potentially remaining infectious for up to 20 days. Asymptomatic individuals can also shed the virus and transmit it to others.
Vaccination status can also impact contagiousness. While vaccines do not always prevent infection entirely, mRNA vaccines have been shown to reduce the infectiousness of individuals with COVID-19, thereby limiting transmission. Immunity from prior infection can also limit contagiousness, though this immunity may fade more quickly than vaccine-induced immunity.
Rapid antigen tests and PCR tests offer different insights into contagiousness. PCR tests are highly sensitive and can detect even small amounts of viral genetic material, sometimes long after a person is no longer infectious. In contrast, rapid antigen tests are less sensitive but are more useful for determining if someone is currently contagious because they detect viral proteins, which indicate active infection. A negative rapid antigen test makes contagiousness highly unlikely.
Criteria for Ending Isolation
Current public health guidance, such as that from the Centers for Disease Control and Prevention (CDC), recommends a symptom-based approach for ending isolation rather than a fixed number of days. Individuals can cease isolation once they have been fever-free for at least 24 hours without the use of fever-reducing medication and their overall symptoms are improving. This updated guidance applies to COVID-19 as well as other respiratory illnesses like the flu and RSV.
After ending isolation, it is still recommended to take additional precautions for five days. These precautions include wearing a well-fitting mask, limiting close contact with others, and improving air quality by gathering outdoors or in well-ventilated areas. If symptoms worsen or a fever returns during this period, individuals should revert to staying home until their symptoms improve again and they are fever-free for another 24 hours.