In amongst the coverage of COVID-19, there have been many references to the seasonal flu, including by Donald Trump. Whilst the two viruses both cause respiratory disease and spread the same way (via small droplets of fluid from the nose and mouth of someone who is sick), there are important distinctions to make between influenza and COVID-19. Not least of all, because our knowledge of the former greatly outweighs that of the latter.
At the time of writing, there have been almost 130,000 confirmed cases of the novel coronavirus, of whom over 69,000 have recovered and more than 5,000 have died. In a typical flu season, the World Health Organization (WHO) estimates that there are about 290,000 to 650,000 respiratory deaths and about 3 to 5 million cases of severe illness.
But these figures alone do not tell the whole story. At a briefing last week, WHO Director-General Tedros Adhanom Ghebreyesus stressed the different mortality rates between the two viruses. “Globally about 3.4 percent of reported COVID-19 cases have died,” Tedros explained. “By comparison, seasonal flu generally kills far fewer than 1 percent of those infected.”
Fatality rates for COVID-19 have varied in studies already. One estimate of a 2.3 percent case fatality in mainland China, the epicenter of the disease, was published in the China CDC Weekly last month. Whereas another study published a few weeks later in the New England Journal of Medicine found that the overall death rate was lower, at around 1.4 percent, using data from over 1,000 patients also in mainland China.
Case fatality rates are expected to fluctuate further as the pandemic progresses, as more mild cases become confirmed. They have also varied significantly amongst different age groups, with older adults hit the hardest. For those 80 and older, one study saw a death-rate of 14.8 percent. However, the overall rate continues to be significantly higher than for seasonal influenza, which is often cited as having a case fatality rate of approximately 0.1 percent.
One of the predominant factors for COVID-19 causing more severe disease than seasonal influenza is its novelty and uniqueness. “While many people globally have built up immunity to seasonal flu strains, COVID-19 is a new virus to which no one has immunity,” Tedros said in the briefing.
Immunity can be built from exposure to the disease, including in the form of a vaccine. Flu vaccines are available to help the body safely develop immunity to the disease, and recent studies have indicated its effectiveness, which can vary season to season, is between 40 percent and 60 percent. However, there is currently no vaccine to prevent COVID-19. Globally, around 20 are in development and 80 clinical trials are set to be launched, but until then there is little immunity in the world population against the virus.
How easily the viruses spread is another way in which COVID-19 and seasonal influenza appear to differ. A basic reproduction number, or R0, is a measure scientists use to estimate the average number of people who catch the virus from a single infected person. For the flu, this number is reportedly around 1.3, but in preliminary studies of COVID-19, R0 is estimated between 2 and 3, similar to that of SARS.
As with a lot of information about the novel coronavirus, these numbers are dynamic and can vary by location and other factors. Scientists are also working to understand more about the point at which COVID-19 can be transmitted. Recent reports suggest that it takes on average 5.1 days before symptoms of the disease emerge, but it is currently unknown whether a person can transmit the disease before this time.
In the meantime, for the best protection against COVID-19, you should follow the expert’s advice on preventative measures, such as washing hands thoroughly, covering coughs and sneezes, avoid touching eyes, nose and mouth, and avoid close contact with people who are sick. If you experience a fever, cough, and difficulty breathing, you should seek medical attention and follow the guidelines to self-isolate.