Thread by @Vaccinologist

As the #COVID19 #outbreak evolves, comparisons have been made with #influenza. Both cause respiratory disease but there are important differences between #SARSCoV2 #virus causing COVID-19 & the influenza virus causing the #flu [from WHO COVID situation report 06.03.2020] #scicomm

Similarity #1. Both #COVID19 & the #flu have a similar disease presentation. Both cause respiratory disease, which presents as a wide range of illness from asymptomatic or mild through to severe disease and even death.

Similarity #2. Both #SARSCoV2 & #influenza viruses are transmitted by contact, droplets & fomites so same #publichealth measures (hand hygiene, good respiratory etiquette (coughing into elbow / into a tissue, immediately disposing of the tissue) are important to prevent infection

Difference #1. Speed of transmission. #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 #SARSCoV2 virus causing #COVIDー19.

The serial interval for #SARSCoV2 #virus is estimated to be 5-6 days, while for the #influenza virus, the serial interval is 3 days. This means that the #flu can spread faster than #COVIDー19.

Furthermore, transmission in the first 3-5 days of illness, or potentially pre-symptomatic transmission (transmission of the #virus before appearance of symptoms) is a MAJOR driver of transmission for #influenza.

In contrast, while we are learning that there are people who can shed #SARSCoV2 #virus 24-48 hours prior to symptom onset, at present, this does NOT appear to be a major driver of transmission for #COVIDー19.

The reproductive number (R0) - # of secondary infections generated from 1 infected individual - is understood to be between 2 and 2.5 for #SARSCoV2, higher than for #influenza. But estimates for both viruses are very context & time-specific so direct comparisons are difficult.

#Children are important drivers of #flu transmission in the community. But initial data for the #SARSCoV2 virus causing #COVID19 shows children are less affected than adults & clinical attack rates in the 0-19 age group are low. Children are infected from adults, not vice versa.

Difference #2. For #COVID19, data to date suggest 80% of infections are mild / asymptomatic, 15% are severe infection, requiring oxygen and 5% are critical infections, requiring ventilation. Severe and critical cases in COVID-19 more than what is seen for #influenza.

Difference #3. Most at risk for severe #influenza are children, pregnant women, elderly, those with chronic medical conditions, people who are immunocompromised. For #COVID19, our current understanding is that older age & underlying conditions increase risk for severe infection.

Difference #4. Mortality for #COVID19 appears higher, especially seasonal #influenza. True mortality of #SARSCoV2 will take time to fully understand. For seasonal influenza, mortality is usually below 0.1%. But mortality is mainly determined by access to & quality of #healthcare.

Difference #5. Currently no licensed #vaccines or #therapeutics for #COVID19. #Antivirals & vaccines are available for #influenza. While the #flu vaccine is NOT effective against #SARSCoV2, it is highly recommended to get vaccinated each year to prevent flu infection. #FightFlu