Both influenza and COVID-19 disease are caused by infectious respiratory agents and cause symptoms that can look quite similar. Coronaviruses cause both. So, what’s the difference?
Influenza virus. 3D illustration showing surface glycoprotein spikes hemagglutinin purple and neuraminidase orange. Image Credit: Kateryna Kon / Shutterstock
First, let’s see more about how they are the same:
Symptoms and complications
Both the flu and COVID-19 begin as fever, cough, body ache, tiredness, and sometimes vomiting and diarrhea.
Both may begin and end practically unnoticed but can sometimes turn fatal, especially in the elderly and in those with weakened immunity.
Both can cause pneumonia.
Both spread via respiratory droplets, that is, by coughing, sneezing or talking. For this reason, people should stay about 6 feet away from others, and avoid touching their nose, eyes, and mouth without sanitizing or washing their hands properly.
Both may be spread for several days by an infected person who is still asymptomatic.
There is no specific drug against either infection.
Symptomatic therapy is advised for both; antipyretics to bring down high fever, plenty of fluids, and ventilation if the patient develops severe respiratory difficulty.
Both may be prevented by frequently washing the hands thoroughly, avoiding unprotected sneezing and coughing, staying away from people who are sneezing or coughing and keeping at home, and away from older adults, if one is sick. Social distancing, or avoiding gatherings of people, is advised to prevent the spread of COVID-19 over large numbers of people.
How are they different?
Anosmia (loss of sense of smell) and ageusia (loss of sense of taste) are significant early symptoms in otherwise asymptomatic patients with COVID-19 infection, occurring in 33% to 66% of patients. In most cases, this is not associated with a runny nose or with sneezing. Less than 5% of patients with COVID-19 get the sniffles, according to Chinese data.
Fever, cough, and sore throat are more common in flu, and are of sudden onset, while a sore throat is less common in COVID-19.
Headaches, body pain, and tiredness are more common in flu than in COVID-19 but are not sufficiently sensitive to discriminate between the two.
As a result, CDC guidelines say anyone with these symptoms and has been in contact with a confirmed case or lives in a place with confirmed cases should call their healthcare provider for advice.
Novel Coronavirus SARS-CoV-2 Colorized scanning electron micrograph of a cell showing morphological signs of apoptosis, infected with SARS-COV-2 virus particles (orange), isolated from a patient sample. Image captured at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
It is thought that COVID-19 may be spread via tiny droplets dispersed in the air even after the infected person is no longer present – this is called airborne transmissions – in contrast, to direct droplet transmission only in the flu.
Children are crucial in the spread of influenza but are little affected by COVID-19 for unexplained reasons.
There are flu vaccines which are formulated every year to induce immunity against the most common strains of the flu, but there is no vaccine against COVID-19 at present.
The measure of contagion of a virus is called the basic reproduction number, R0. R0 refers to the number of people secondarily infected from one infected person. In the case of COVID-19, the R0 is estimated to be 2-2.5, which means one person suffering from COVID-19 is likely to infect 2 to 2.5 people. This is higher than the R0 of 1.3 for the flu.
The incubation period for COVID-19 is, however, more extended than for the flu. The serial interval is a term used to denote the speed between successive infections, which is about three days for flu but about 4-6 days for COVID-19. The spread of the novel 2019 coronavirus in the period before the person becomes symptomatic is limited compared to the flu virus. However, newer research indicates that up to 13% of cases may have been acquired in this manner.
However, COVID-19 appears to be more deadly, more contagious, and causes far more burden on the health system, not merely because of its exponential spread, but because of the high percentage of patients (20%) who become severely ill and require mechanical ventilation (5%), according to WHO statistics. Of these patients, many do not survive.
This is in sharp contrast to the 1-2% of flu patients who require hospitalization, which still comes to half a million patients in the US over the period from early October to the beginning of March. The length of hospital stay for COVID-19 patients is almost double that of a flu patient (5-6 days on average), which means a heavier burden on the health system.
The novel 2019 coronavirus which is officially called the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the single cause of COVID-19 while influenza is caused by multiple strains and types of influenza viruses.
The flu causes about a billion cases globally each year, with 290,000 to 640,000 deaths worldwide – a mortality rate of 0.1%. COVID-19 is reported to have affected about 2.56 million people worldwide, with over 176,000 deaths so far (April 22, 2020) for a mortality rate of 6.875% in reported cases. On the other hand, given the very poor coverage of cases, it is likely that the number of infections by the novel coronavirus is far more significant than reported so far. Therefore the true mortality rate is far lower.