Beginning again in 2024-2025, all flu vaccines in the United States will be “trivalent” vaccines, which means they protect against three different influenza viruses: an influenza A(H1N1) virus, an influenza A(H3N2) virus, and an influenza B/Victoria virus.
Trivalent flu vaccines are approved for use in many countries. Both trivalent and quadrivalent flu vaccines are expected to offer similar protection against the flu viruses they protect against. B/Yamagata flu viruses have not circulated in the population since March 2020, so protection from trivalent and quadrivalent flu vaccines is expected to be similar.
Sources: