What Are Some of the Common Symptoms of COVID-19 and Flu?

A person generally shows symptoms within one to four days after exposure to the virus causing flu. However, a person takes longer to experience symptoms of COVID-19. It may take anywhere from 2 to 14 days following an infection or exposure.

Adults and older children with the flu appear to be most contagious one day before showing symptoms and during the first three to four days of their illness. Typically, the period of spread is less than seven days. However, infants and people with weakened immune systems can be contagious for longer.

Studies of prior variants, including Delta, have revealed that people with COVID-19 infection on average begin spreading the virus two to three days before experiencing the symptoms and can continue to shed the virus for about eight days after their symptoms begin.

In both cases, the virus can spread to others by people who have mild symptoms or even when they show no symptoms at all.

The virus in both cases spreads similarly via small or large droplets in the air, which are shed by the person harboring the virus in the body (while coughing, sneezing, or talking) or by touching surfaces that inhabit the virus on it. They could be the infected hands of the person or other inanimate objects touched by the person with the virus (called fomites). The virus then multiplies in the other person when it reaches their mouth, nose, or lungs.

COVID-19 virus spread differs in being more contagious leading to faster and continual spread.

Severe cases of both infections when untreated can result in complications, including:

• Pneumonia
• Respiratory failure
• Worsening of chronic medical conditions of the lung and diabetes
• Heart attacks
• Stroke
• Sepsis (a life-threatening illness caused by the extensive spread of infection throughout the body)
• Multiple-organ failure
• Secondary infections (bacterial or fungal infections)

Flu, unlike COVID-19, generally does not proceed to complications and resolves on its own, rarely requiring hospitalization or causing death.

COVID-19 can have the following complications:

• Blood clots in the veins and arteries of the lungs, heart, legs, or brain
• Multisystem inflammatory syndrome in children (MIS-C) and adults (MIS-A)
• Long COVID-19 syndrome

The U.S. Food and Drug Administration annually licenses multiple influenza vaccines to protect against the flu viruses.

The FDA has authorized three COVID-19 vaccines for use in the United States to help prevent COVID-19.

• Pfizer-BioNTech and Moderna are the preferred COVID-19 mRNA vaccines.
• Johnson & Johnson’s Janssen COVID-19 vaccine is also in use.

These must be followed by appropriate boosters as and when needed.