How many types of influenza viruses are included in vaccines each year?

How many types of influenza viruses are included in vaccines each year?

• A. Two
• B. Three
• C. Four
• D. Five

Answer: (B)

Seasonal flu vaccines are multivalent, designed to cover several circulating viruses in one shot. Traditionally, the standard formulation includes three strains: two influenza A strains (H1N1 and H3N2) and one influenza B strain. This three-strain setup aims to provide broad protection against the most likely viruses each season. Some vaccines, however, are quadrivalent and include a second influenza B strain, bringing the total to four. So, in the classic trivalent formulation, three types of influenza viruses are included.

Seasonal flu vaccines are multivalent, designed to cover several circulating viruses in one shot. Traditionally, the standard formulation includes three strains: two influenza A strains (H1N1 and H3N2) and one influenza B strain. This three-strain setup aims to provide broad protection against the most likely viruses each season. Some vaccines, however, are quadrivalent and include a second influenza B strain, bringing the total to four. So, in the classic trivalent formulation, three types of influenza viruses are included.