Similarities and Differences between COVID-19 and Influenza (Flu)

Most of us are usually confused with the similarities and differences between COVID-19 and Influenza as these two have similar symptoms and disease presentation as well. So, let us have a look at the similarities and differences between COVID-19 and Influenza.

Table of Contents

Introduction of Influenza

Shorter median incubation period (time from infection to appearance of symptoms).
Influenza has shorter serial interval of 3 days.
The number of secondary infections generated in case of influenza is less compared to COVID-19.
Children are important drivers of influenza virus transmission in the community.
For seasonal influenza, mortality is usually well below 0.1%.
Antivirals and vaccines available for influenza.

Introduction of COVID-19

Coronaviruses are a large family of viruses, some causing illness in people and others that circulate among animals, including camels, cats and bats.
Coronaviruses are zoonotic viruses i.e. they are transmitted between animals and people.
Corona virus disease is now commonly known as COVID-19.
COVID-19 has longer incubation period than influenza.
It has longer serial interval ranging from 5-6 days.
The number of secondary infections generated from one infected individual – is understood to be between 2 and 2.5 for COVID-19 virus.
Usually, children are less affected than adults and that clinical attack rates in the 0-19 age group are low for COVID-19.
Mortality for COVID-19 appears to be higher than influenza, especially seasonal influenza. As per the data so far, crude mortality ratio (the number of reported deaths divided by the reported cases) is between 3-4%.
New vaccines have been developed for COVID-19 by different countries. These vaccines have different potency and effectiveness. At the same time, new vaccines are also under trial.

Similarities between Influenza (Flu) and COVID-19

COVID-19 and influenza are both contagious respiratory diseases.
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.
Both infections are caused by viruses (COVID-19 by SARS-CoV-2 virus and influenza by Influenza virus)
Both spread mainly between people who are in close contact with each other
COVID-19 and Influenza (Flu) both predominantly affect the respiratory system.
Both are transmitted by contact, droplets and fomites.
Similar symptoms: cough, runny nose, sore throat, fever, headache and fatigue.
Complications in COVID-19 and influenza are: Pneumonia, acute respiratory distress syndrome, organ failure, heart attacks, heart or brain inflammation, stroke
Both can be fatal if not treated/managed timely.
Similar protective measures can be used to be protected from both infections
Similar 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.
Both infections can be prevented through vaccinations.

Differences between Influenza and COVID-19:

Basis of differences	Influenza	COVID-19
Speed of Transmission	Shorter median incubation period (time from infection to appearance of symptoms)	Longer median incubation period than influenza
Serial Interval (the time between successive cases)	Shorter serial interval. The serial interval for influenza is 3 days.	Longer serial interval. The serial interval for COVID-19 virus is estimated to be 5-6 days
Speed of Spread	Speed of spread is slow than COVID-19	Spreads much faster than Influenza
Time of Transmission	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	We are learning that there are people who can shed COVID-19 virus 24-48 hours prior to symptom onset. But, at present, this does not appear to be a major driver of transmission
Reproductive Number	The number of secondary infections generated in case of influenza is less compared to COVID-19.	The number of secondary infections generated from one infected individual – is understood to be between 2 and 2.5 for COVID-19 virus
More vulnerable population	Children are important drivers of influenza virus transmission in the community.	Initial data indicates that children are less affected than adults and that clinical attack rates in the 0-19 age group are low.
Fraction of infection	Fractions of severe and critical infection is less compared to COVID-19.	Fractions of severe and critical infection would be higher than influenza infection. 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
Who Are At More Risk?	Those most at risk for severe influenza infection are children, pregnant women, elderly, those with underlying chronic medical conditions and those who are immunosuppressed.	As per the current understanding, older age and underlying conditions increase the risk for severe infection of COVID-19.
Mortality Ratio	Mortality is less compared to COVID-19. For seasonal influenza, mortality is usually well below 0.1%.	Mortality for COVID-19 appears to be higher than influenza, especially seasonal influenza. As per the data so far, crude mortality ratio (the number of reported deaths divided by the reported cases) is between 3-4%.
Availability of Vaccines/Therapeutics	Antivirals and vaccines available for influenza	New vaccines have been developed for COVID-19 by different countries. These vaccines have different potency and effectiveness. At the same time, new vaccines are also under trial.