COVID-19 is the greatest pandemic of this century in terms of scope and speed, with the highest number of global mortality, with the majority of deaths occurring in high-income countries. The infection fatality rate is driven by risk factors such as growing age, obesity, and comorbidities such as lung disorders, diabetes, cancer, and neurological diseases. Infectious diseases are illnesses brought on by bacteria, viruses, fungi, or parasites. Our bodies are home to a variety of creatures. In most cases, they're innocuous or even beneficial. However, some microbes can cause disease under particular circumstances. Emerging infectious disease epidemics are most likely to start in wildlife, and they're on the rise thanks to socioeconomic, environmental, and ecological variables, as well as increased mobility and globalisation, including climate change. The individuals most at risk, such as pregnant women for Zika and the elderly for COVID-19, the vectors of transmission, the mortality rate, and the transmissibility, which is generally assessed as the basic reproduction number, differ in many ways.