How the flu changes and affects the vaccine effectiveness

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Changes in the surface antigens of a virus (the H & N) result in a constantly changing flu virus. This can occur in 2 ways:

	Antigenic drift: refers to minor changes (natural mutations) in genes of flu viruses that occur gradually over time to a point where the body’s immune system and antibodies may no longer recognise the antigen and can no longer provide protection from this new version of the virus.
	Antigenic shift: This is the combination of two or more different strains of virus. This abrupt, major change results in a new subtype. Previous exposure may not give protection against this new subtype and can potentially lead to an epidemic or pandemic.

The World Health Organization (WHO) monitors flu epidemiology throughout the world. Each year WHO make recommendations of which strains of influenza A and B should be included in the vaccine for the coming flu season. These recommendations are based on the predicted circulating strains, in a particular region, in the forthcoming winter.

Changes in the surface antigens of a virus (the H & N) result in a constantly changing flu virus. This can occur in 2 ways:

Antigenic drift: refers to minor changes (natural mutations) in genes of flu viruses that occur gradually over time to a point where the body’s immune system and antibodies may no longer recognise the antigen and can no longer provide protection from this new version of the virus.

Antigenic shift: This is the combination of two or more different strains of virus. This abrupt, major change results in a new subtype. Previous exposure may not give protection against this new subtype and can potentially lead to an epidemic or pandemic.

Pharmacy Excellence - Flu Refresher 2024 / 2025

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Changes in the surface antigens of a virus (the H & N) result in a constantly changing flu virus. This can occur in 2 ways:

Antigenic drift: refers to minor changes (natural mutations) in genes of flu viruses that occur gradually over time to a point where the body’s immune system and antibodies may no longer recognise the antigen and can no longer provide protection from this new version of the virus.

Antigenic shift: This is the combination of two or more different strains of virus. This abrupt, major change results in a new subtype. Previous exposure may not give protection against this new subtype and can potentially lead to an epidemic or pandemic.

Pharmacy Excellence - Flu Refresher 2024 / 2025

Continue Module