Why is it necessary to receive a flu shot every year?

Receiving a flu shot every year is necessary primarily because it ensures that the vaccine matches the current virus strains circulating in the population. Each year, the influenza virus undergoes changes, with different strains emerging or becoming more dominant. This constant evolution necessitates an annual update to the vaccine formulation to provide optimal protection.

The effectiveness of a flu vaccine directly ties to its ability to match the circulating strains of the virus. If the vaccine does not align with the prevalent strains, it may not effectively prevent infection. Therefore, annual vaccination is crucial to maintain an up-to-date defense against the flu and to help reduce the risk of widespread outbreaks.

While other points may touch on related aspects of vaccination and immunity, they do not specifically address the critical reason for annual vaccination as related to the changing nature of the virus itself.