COVID-19 is More Contagious Than Influenza
COVID-19 (SARS-CoV-2) is significantly more contagious than seasonal influenza, as evidenced by continued community spread despite mitigation measures that virtually eliminated influenza transmission. 1
Direct Evidence of Greater Contagiousness
The most compelling evidence comes from the 2019-2020 respiratory illness season when COVID-19 mitigation measures (social distancing, hand hygiene, masks) were implemented globally:
- Influenza cases dropped to near-zero levels in both northern and southern hemispheres after COVID-19 prevention measures were introduced, with the 2019-2020 influenza season ending 4-7 weeks early in northern hemisphere countries 1
- Despite this dramatic reduction in influenza, COVID-19 continued to spread in communities, demonstrating that SARS-CoV-2 transmits more efficiently than influenza even under identical prevention conditions 1
- This natural experiment provides direct comparative evidence that COVID-19 is substantially more contagious than influenza 1
Clinical Impact of Higher Contagiousness
The greater transmissibility translates to more severe population-level health impacts:
- In-hospital mortality is nearly 3 times higher for COVID-19 compared to influenza (age-standardized mortality ratio of 2.82) 2
- COVID-19 patients require more intensive medical resources, with 15-fold higher odds of ICU admission (AOR = 15.3) and ventilator use (AOR = 15.6) compared to influenza 3
- Hospital stays are significantly longer for COVID-19, averaging 3.2 additional days compared to influenza 4
- Overall mortality during hospitalization is 20 times higher for COVID-19 (AOR = 19.8) 3
Transmission Characteristics
Both diseases spread through respiratory droplets, but key differences exist 5:
- SARS-CoV-2 transmits via asymptomatic individuals, making it harder to control through symptom-based screening alone 5
- Influenza patients are more likely to be symptomatic, with only 6.6% of infected children showing no symptoms 5
- Bacterial co-infections are less common with COVID-19 (5.1%) compared to influenza (11-35%), though secondary bacterial infections are more frequent in COVID-19 5
Clinical Pitfalls
Do not assume similar risk profiles between the two diseases:
- COVID-19 affects younger adults more severely than influenza relative to their baseline health, with deaths in younger COVID-19 patients less often related to underlying conditions 3
- Racial disparities differ markedly: White non-Hispanic persons comprised 64% of influenza hospitalizations but only 37% of COVID-19 hospitalizations 3
- The intrinsic virulence of COVID-19 is higher, affecting multiple organ systems including immune response, coagulation, cardiac function, and metabolism more severely than influenza 6