Why do flu viruses mutate so much?

Why do flu viruses mutate so much?

• A. DNA virus, high fidelity
• B. Mutations occur only in the presence of antiviral pressure
• C. Co-infection reduces mutation rates
• D. RNA virus, so poor fidelity when replicating

Answer: (D)

Influenza mutates a lot because it is an RNA virus, and its RNA-dependent RNA polymerase copies the genome with low fidelity. That means errors are introduced during replication frequently, accumulating over time. These mutations often occur in surface proteins like hemagglutinin and neuraminidase, driving antigenic drift that lets the virus partly escape preexisting immunity. This ongoing, gradual change is a hallmark of RNA viruses and explains why flu vaccines need updating regularly. Mutations aren’t only produced when antivirals are present; they arise as a normal part of replication. Co-infection can lead to genome segment reassortment, creating new strain combinations, but that’s a separate mechanism from the baseline high mutation rate. DNA viruses, which have proofreading polymerases, generally mutate more slowly, so the idea that a DNA virus would show high fidelity isn’t applicable to influenza.

Influenza mutates a lot because it is an RNA virus, and its RNA-dependent RNA polymerase copies the genome with low fidelity. That means errors are introduced during replication frequently, accumulating over time. These mutations often occur in surface proteins like hemagglutinin and neuraminidase, driving antigenic drift that lets the virus partly escape preexisting immunity. This ongoing, gradual change is a hallmark of RNA viruses and explains why flu vaccines need updating regularly.

Mutations aren’t only produced when antivirals are present; they arise as a normal part of replication. Co-infection can lead to genome segment reassortment, creating new strain combinations, but that’s a separate mechanism from the baseline high mutation rate. DNA viruses, which have proofreading polymerases, generally mutate more slowly, so the idea that a DNA virus would show high fidelity isn’t applicable to influenza.