Produced as quadrivalent recombinant influenza vaccine, Flublok® is considered to be the next generation of influenza immunization, and is classified as the competent seasonal influenza vaccination for the 2021/2022 season in Hong Kong. Any individual aged 18 years or above will be eligible for taking the quadrivalent vaccine, and it could yield better protection than the traditional influenza vaccines. Comparing to the standard quadrivalent inactivated influenza vaccine, it is proven to be 30% more effective in preventing flu for the population aged 50 years or above, and the hemagglutinin (HA) antigen per strain is triple to the ordinary vaccine as well. Apart from that, the new vaccine can offer 40% additional cross-protection than standard vaccine, i.e. can still offer protection to the recipients towards virus strains other than those specified in vaccine.