A pandemic is when a disease affects the global population. Pandemics are usually caused by new infectious agents (bacteria or viruses) that spread quickly. A pandemic is a type of epidemic, however a pandemic involves the number of people and the geographical area that the disease affects.
Acute COVID-19. Once symptoms appear, you have entered the acute stage. You may have fever, cough and other COVID-19 symptoms. Active illness can last one to two weeks if you have mild or moderate coronavirus disease, but severe cases can last months.
Immunity is complicated and, yes, you can still get reinfected with COVID-19. In fact, a recent study found that unvaccinated adults were twice as likely to get reinfected with COVID-19 than those who got vaccinated after they'd recovered from their illness.