Quadrivalent Influenza Vaccine is a type of flu vaccine designed to protect against four different flu viruses. In this clinical trial, the vaccine is being tested in two forms: a high-dose version and a standard-dose version. The goal is to see which version is more effective in preventing serious flu-related illnesses, like hospitalization due to influenza or pneumonia, in older adults aged 65 to 79 years. The vaccine works by stimulating the body’s immune system to recognize and fight the flu virus, helping to reduce the risk of getting sick.

Influenza – Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. It primarily affects the nose, throat, and sometimes the lungs. The disease typically begins suddenly and can cause symptoms such as fever, cough, sore throat, muscle aches, and fatigue. Influenza spreads through droplets when an infected person coughs, sneezes, or talks. The virus can also be contracted by touching surfaces contaminated with the virus and then touching the face. The illness can range from mild to severe and can lead to complications, especially in older adults and those with weakened immune systems.

Pneumonia – Pneumonia is an infection that inflames the air sacs in one or both lungs, which may fill with fluid or pus. It can be caused by bacteria, viruses, or fungi. Symptoms often include cough with phlegm or pus, fever, chills, and difficulty breathing. The disease can vary in severity from mild to life-threatening, with the severity often depending on the type of germ causing the infection, as well as the age and overall health of the individual. Pneumonia is spread through airborne droplets from a cough or sneeze, or by touching contaminated surfaces. It is more common in older adults, infants, and those with other health problems.