What is the difference between Influenza and COVID-19 ?

What is the difference between Influenza and COVID-19 ?

Both COVID-19 and Influenza cause respiratory disease; however, 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?
  • COVID-19 and influenza viruses both cause respiratory disease, which presents as a wide range of illness from asymptomatic or mild through to severe disease and death.
  • Both viruses are transmitted by contact, droplets and fomites (objects or materials that are likely to carry infection, such as clothes, furniture, utensils…)) Therefore, 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 to be taken 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 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. 
  • Transmission in the first 3-5 days of illness, or transmission of the virus before the appearance of symptoms is a major factor in 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 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.
  • Although the range of symptoms for the two viruses is similar, the fraction with severe disease appears to be different. For COVID-19, current data 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, current understanding is that older age and underlying conditions increase the risk for severe infection.
  • Mortality For seasonal influenza, is usually well below 0.1%. It is important to note that, mortality is, to a large extent determined by access to and quality of health care. In the case of COVID-19 mortality appears higher than for influenza, especially seasonal influenza. The true mortality of COVID-19 will take some time to fully understand, but the data so far indicates 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.
What medical interventions are available for COVID-19 and influenza viruses?

Antivirals and vaccines are available for treatment of influenza; and although the influenza vaccine is not effective against COVID-19 virus, it is highly recommended to get vaccinated each year to prevent influenza infection. 

At present, there are currently no licensed vaccines or therapeutics for COVID-19.  However, there are a number of therapeutics currently in clinical trials in China; and more than 20 vaccines in development.

For further information, see here.