What Is The Contagious Period After Catching A Virus?

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Ask anyone, and they will probably tell you that nothing good came out of the pandemic. However in the scientific world, it did manage to bring heightened awareness of how viruses, especially respiratory ones, can easily spread from person to person.

The era of individuals bravely “toughing it out” and attending offices or schools while sick seems to be fading away. However, despite this collective awareness, there remains a lack of consensus on when and how to safely return to normalcy, including the continued use of precautions like masks.

Exploring the contagious nature of illnesses such as colds, flu, COVID-19, and RSV, it becomes crucial to understand the varying timelines of contagion and the factors influencing them.

What Is the Contagious Period for a Common Cold?

Dean Winslow, MD, an infectious-disease physician at Stanford Medicine in California, emphasizes the importance of recognizing the contagious periods for each ailment.

Dr. Winslow said, “Colds are caused by many different viruses, and rhinovirus (which has many types) is the most common cause.” Meanwhile, other common cold viruses include adenoviruses and coronaviruses.

Dr. Winslow explains that this is the reason you can get multiple colds in a single season, because they tend to be caused by different strains or viruses.

According to the Centers for Disease Control and Prevention (CDC), colds are spread from person to person through the air and from close personal contact. In addition, the most common symptoms nasal congestion, sneezing, cough, sore throats, and sometimes – albeit rarely – fever.

“You can actually be contagious for up to a day or so prior to onset of your symptoms, and then usually you’re most contagious for about 24 to 48 hours after onset of symptoms,” says Dr. Winslow.

Dr. Winslow says that for the common cold, known for its relatively high contagion, individuals are advised to wear masks for approximately five or six days after symptoms appear. This precautionary measure aims to protect others, as the amount of virus shed diminishes significantly by that time.

What is the Contagious Period for the Flu?

Moving to the flu, caused by influence A and B viruses, the transmission occurs through airborne droplets and contact with contaminated surfaces, says the CDC.

The symptoms of the flu can range from mild to severe. These include fever, cough, chills, runny or stuffy nose, sore throat, headaches, fatigue, muscle aches, vomiting and diarrhea, however these GI symptoms tend to be more common in children.

The primary mode of influenza transmission involves the dispersal of miniscule droplets into the air when infected individuals cough, sneeze, or talk. These airborne particles may subsequently land in the mouths or noses of others, facilitating the spread of the flu.

Additionally, transmission can occur through contact with contaminated surfaces; for instance, if an individual touches an object carrying the flu virus and subsequently touches their nose or mouth. However, this method of transmission is less frequent.

Dr. Winslow says that like with a cold, you can shed the flu virus and infect other people up to 24 hours prior to onset of symptoms. “You’re most contagious the first day or two after the onset of symptoms,” he says.

Moreover, he says, by day three or four, you may still have a lot of symptoms as a result of your immune system being activated, but the amount of virus that you’re shedding is lower. “Even though it’s less likely to spread by that point, you are still potentially contagious. To be safe, I would recommend that people wear a mask pretty much the whole time they have upper respiratory symptoms,” says Dr. Winslow.

While the flu shot can reduce the risk of infection, there is limited evidence indicating that prior vaccination affects the duration of contagion.

Dr. Winslow adds that there is insufficient evidence to demonstrate that pre-existing flu vaccination has an impact on the duration of contagion in individuals who still contract the virus.

But, Dr. Winslow also adds that taking a medication like Tamiflu, consumed  within the first 48 hours after onset of symptoms, probably does make you less contagious. “It definitely reduces the duration of symptoms and also very likely has at least a modest effect on reducing viral shedding because it is an antiviral,” he says.

What is the Contagious Period for RSV?

Yale Medicine notes that Respiratory Syncytial Virus (RSV) is a highly contagious virus that induces inflammation in the respiratory tract, typically manifesting in mild, cold-like symptoms. Distinguishing between a common cold and RSV can be challenging, but RSV often involves increased mucus production, leading to a higher consumption of tissues.

According to the CDC, individuals infected with RSV typically exhibit symptoms within four to six days after the initial exposure. Common RSV symptoms include a runny nose, decreased appetite, coughing, sneezing, fever and wheezing, as outlined by the CDC.

The transmission of RSV occurs through various means, including airborne droplets released when an infected person coughs or sneezes. Direct contact, such as kissing someone with RSV, and touching contaminated surfaces, like doorknobs, and subsequently touching the mouth, nose, or eyes, also contribute to the spread of the virus, as explained by Yale Medicine.

Moreover, individuals can spread RSV a day or two before symptoms become apparent and typically remain contagious for about three to eight days after exposure, according to the CDC. After the initial symptomatic period, the viral shedding diminishes significantly, unless the immune system is compromised, as highlighted by Dr. Winslow.

The CDC indicates that some infants and adults with weakened immune systems may struggle to eliminate the virus as effectively as health adults, remaining contagious for up to four weeks. However, these extended contagious periods are primarily observed in individuals with compromised immune systems.

Dr. Winslow emphasizes that the RSV vaccine, although relatively new, lacks conclusive evidence regarding its impact on the duration of contagiousness. The extent to which the vaccine influences the contagious period for RSV remains uncertain and requires further research.

What is the Contagious Period for COVID-19?

COVID-19 is very contagious at this point, says Dr. Winslow. “The way the virus has evolved is that it’s tended to become more contagious and cause less disease, which is a common strategy that most pathogens take in terms of their evolution,” he explains.

Like the flu, symptoms of COVID-19 can range from mild to severe. These include headache, cough, fever, chills, sore throat, shortness of breath, muscle or body aches, fatigue, congestion or runny nose, nausea, vomiting and diarrhea.

The transmission of the COVID-19 virus occurs through droplets and tiny particles exhaled by individuals with the infection. Others can become infected if these particles are inhaled or come into contact with their eyes, noses, or mouths. Additionally, there is a less common mode of transmission where virus particles land an surfaces and are then spread through contact.

“Research has confirmed that you can be contagious up to 24 hours prior to onset of symptoms and then you are most contagious one to two days after the onset of symptoms,” says Winslow.

The duration of contagiousness is influenced by the severity of the illness. According to the CDC, individuals infected with COVID-19 who are asymptomatic or have mild symptoms should isolate for at least five days, starting from the day symptoms appeared or the date of a positive test day (day 0). The CDC further advises continuing masking through day 10 or until a negative test result.

For those with moderate or severe COVID-19, isolation is recommended through at least day 10. Individuals with severe cases may remain infectious beyond this period and might need to extend isolation for up to 20 days. People who are moderately or severely immunocompromised may have a more prolonged contagious period, necessitating isolation through at least day 20. Serial testing and consultation with an infectious-disease specialist are advised to determine the appropriate end of isolation.

Even if vaccinated against COVID-19, individuals who contract the infection can still spread the virus. However, a Harvard study suggests that vaccinated individuals may be less contagious, shedding the virus for a shorter period. This underscores the importance of continued adherence to preventive measures.

The correlation between symptom severity and viral load implies that individuals with preexisting immunity from vaccination are less likely to shed the virus, as explained by Dr. Winslow.

The correlation between symptom severity and viral load implies that individuals with preexisting immunity from vaccination are less likely to shed the virus, as explained by Dr. Winslow.

While antiviral drugs like Paxlovid, when taken shortly after symptoms start, may reduce viral shedding, Dr. Winslow emphasizes the necessity of following recommendations on making and isolation to effectively manage the spread of the virus.