As the COVID-19 outbreak continues to evolve, comparisons have been drawn to influenza. Both cause respiratory disease, yet there are important differences between the two viruses and how they spread. This has important implications for the public health measures that can be implemented to respond to each virus.
How are COVID-19 and influenza viruses similar?
In the first place, COVID-19 and influenza viruses have a similar disease presentation. That is, they both cause respiratory disease, which presents as a wide range of illness from asymptomatic or mild through to severe disease and death.
Secondly, both viruses are transmitted by contact, droplets and fomites. As a result, the same public health measures, such as hand hygiene and good respiratory etiquette (coughing into your elbow or into a tissue and immediately disposing of the tissue), are important actions all can take to prevent infection.
How are COVID-19 and influenza viruses different?
The speed of transmission is an important point of difference between the two viruses. Influenza has a shorter median incubation period (the time from infection to appearance of symptoms) and a shorter serial interval (the time between successive cases) than COVID-19 virus. The serial interval for COVID-19 virus is estimated to be 5-6 days, while for influenza virus, the serial interval is 3 days. This means that influenza can spread faster than COVID-19.
Further, transmission in the first 3-5 days of illness, or potentially pre-symptomatic transmission –transmission of the virus before the appearance of symptoms – is a major driver of transmission for influenza. In contrast, while we are learning that there are people who can shed COVID-19 virus 24-48 hours prior to symptom onset, at present, this does not appear to be a major driver of transmission.
The reproductive number – the number of secondary infections generated from one infected individual – is understood to be between 2 and 2.5 for COVID-19 virus, higher than for influenza. However, estimates for both COVID-19 and influenza viruses are very context and time-specific, making direct comparisons more difficult.
Children are important drivers of influenza virus transmission in the community. For COVID-19 virus, initial data indicates that children are less affected than adults and that clinical attack rates in the 0-19 age group are low. Further preliminary data from household transmission studies in China suggest that children are infected from adults, rather than vice versa.
While the range of symptoms for the two viruses is similar, the fraction with severe disease appears to be different. For COVID-19, data to date suggest that 80% of infections are mild or asymptomatic, 15% are severe infection, requiring oxygen and 5% are critical infections, requiring ventilation. These fractions of severe and critical infection would be higher than what is observed for influenza infection.
Those most at risk for severe influenza infection are children, pregnant women, elderly, those with underlying chronic medical conditions and those who are immunosuppressed. For COVID-19, our current understanding is that older age and underlying conditions increase the risk for severe infection.
Mortality for COVID-19 appears higher than for influenza, especially seasonal influenza. While the true mortality of COVID-19 will take some time to fully understand, the data we have so far indicate that the crude mortality ratio (the number of reported deaths divided by the reported cases) is between 3-4%, the infection mortality rate (the number of reported deaths divided by the number of infections) will be lower. For seasonal influenza, mortality is usually well below 0.1%. However, mortality is to a large extent determined by access to and quality of health care.
What medical interventions are available for COVID-19 and influenza viruses?
While there are a number of therapeutics currently in clinical trials in China and more than 20 vaccines in development for COVID-19, there are currently no licensed vaccines or therapeutics for COVID-19. In contrast, antivirals and vaccines available for influenza. While the influenza vaccine is not effective against COVID-19 virus, it is highly recommended to get vaccinated each year to prevent influenza in
Influenza (the flu) and COVID-19, the illness caused by the pandemic coronavirus, are both contagious respiratory illnesses, meaning they affect your lungs and breathing, and can be spread to others. Although the symptoms of COVID-19 and the flu can look similar, the two illnesses are caused by different viruses.
Similarities:
Symptoms
· Both illnesses can cause fever, cough, body aches, and sometimes vomiting and diarrhea (especially in children). Learn more about COVID-19 symptoms.
· Both can result in pneumonia.
· Both flu and COVID-19 can be mild or severe, or even fatal in rare cases.
How it spreads
Both the flu and COVID-19 spread in similar ways. Droplets or smaller virus particles from a sick person can transmit the virus to other people nearby. The smallest particles may linger in the air, and another person can inhale them and become infected.
Or, people can touch a surface with viruses on it, and then transfer the germs to themselves by touching their face.
People infected with the coronavirus or the flu may not realize they are sick for several days, and during that time can unknowingly spread the disease to others before they even feel sick.
Treatment
Neither the flu nor COVID-19 is treatable with antibiotics, which only work on bacterial infections.
Both are treated by addressing symptoms, such as reducing fever. Severe cases may require hospitalisation and very ill patients may need a ventilator — a machine that helps them breathe.
Antiviral medications may shorten the duration of both illnesses.
Prevention
Both can be prevented by mask-wearing, frequent and thorough hand washing, coughing into the crook of your elbow, staying home when sick and limiting contact with people who are infected. Physical distancing limits the spread of COVID-19 in communities.
Source: WHO
