The 1918 influenza pandemic is considered the most devastating pandemic of all time, killing at least 50 million people worldwide. Clinicians and scientists struggled with many unknowns and added confusion that the disease was caused by bacteria rather than a virus. It took 30 years for people to understand that the 1918 influenza pandemic that infected 30% of the world's population was caused by the H1N1 virus.

The H3N2 influenza virus pandemic was first reported in the United States in September 1968. The pandemic's estimated death toll was 1 million worldwide and about 100,000 in the United States. Most deaths from the H3N2 virus occurred in people 65 years of age and older.

Although not as dangerous as other flu diseases, A/H1N1 flu can cause pneumonia and secondary infections, and more seriously, can cause multiple organ failure and lead to death in some at-risk subjects, especially chronic patients and those with underlying diseases.

The humid weather in winter and spring can create favorable conditions for viruses and bacteria to grow. Therefore, it is easy for epidemics to break out in Vietnam as well as many countries around the world. Therefore, we need to strengthen methods to prevent winter and spring epidemics before they risk becoming pandemics.