Covid-19 spreads easily compared to other diseases and there are several factors that explain this.
One reason is the location of the first cells infected by the virus. Calciform cells in the nose become infected quickly and so do the ciliates in the airways. They contain two types of receptors (ACE2 and TMPRSS2), to which the coronavirus connects. And because these cells are in the nose, people easily breathe in and out virus particles.
Covid-19 can spread before a person has symptoms. In many cases, they will neither show these signs nor know that they are infected. These asymptomatic transmissions facilitate the spread of the coronavirus.
The incubation period is relatively long. People with the flu usually feel bad until five days after the infection. But with covid-19, symptoms appear after five or six days or in up to two weeks.
The infectious period of influenza lasts about a week, while that of covid-19 is usually for eight to 10 days or even longer.
This prolonged infection is one reason why the disease caused by the coronavirus spreads so quickly.