Question special

Though this was not a significant finding, the quadrivalent inactivated vaccine had better effectiveness than the trivalent vaccine which would be expected due to additional coverage for B/Victoria viruses. However, the authors noted that ”Against B/Victoria, vaccine effectiveness among participants who had been vaccinated in the previous season was lower than that among those who had not been vaccinated in the previous season”.

What are some reasons for this finding? Does exposure to prior influenza vaccination attenuate the response to future influenza vaccinations? Is this finding limited to particular strains?