Why the Flu Shot Changes Every Year

One of the most common questions about influenza vaccination is also one of the most reasonable: 'If I got it last year, why do I need it again?'

Influenza keeps changing

Influenza viruses evolve continuously. The strains circulating this year are not necessarily identical to the ones that dominated last year.

That is why global surveillance is used to update vaccine composition over time.

Protection also fades

Even when the circulating viruses are similar, immune protection from vaccination decreases with time.

An annual vaccine refreshes that protection before the period when influenza activity usually rises.

Hawaii is a little different

Seasonal influenza circulates in Hawaii year-round, although activity still tends to increase in fall and winter.

That makes influenza prevention especially relevant in a place where travel and year-round movement connect us constantly with the continental U.S. and the rest of the Pacific.

Not perfect does not mean pointless

Flu vaccine effectiveness varies by season, but vaccination can still reduce the risk of influenza, hospitalization, severe complications, and death.

The flu shot is less like installing a permanent lock and more like updating protection against a moving target.

— Nora Phillips, DNP, APRN Central Health | Wahiawa, Hawaii

Sources

Hawaii Department of Health — Influenza. https://health.hawaii.gov/docd/disease_listing/influenza-flu/

CDC — Seasonal Influenza Vaccination. https://www.cdc.gov/flu/vaccines/