Looking at newer enhanced seasonal influenza vaccines: a systematic review of efficacy, effectiveness and safety

In sum, the evidence-base for the efficacy (study results from conducted phase 3 trials) and effectiveness (study results from assessment of vaccine performance when vaccines are in use in the real world) of newer and enhanced influenza vaccines is currently still limited. With several studies ongoing, ECDC will update this review in the future.

Despite the currently limited evidence, it is likely that the use of these vaccines provides greater protection against seasonal influenza than not getting vaccinated. Due to a lack of available studies, a comparison between the newer vaccines was not assessed. A large body of evidence was presented for the safety of the newer influenza vaccines, with expected results regarding the safety profiles.

The report provides recommendations to enhance research conduct as well as reporting on this topic to improve available data overall for these newer enhanced seasonal influenza vaccines.

Why seasonal influenza vaccines?

Seasonal influenza is an infectious respiratory disease, typically circulating from November to April in the Northern hemisphere and from June to October in the Southern hemisphere. It is mainly transmitted between humans through droplet transmission, indirect contact and aerosols. Collectively, the World Health Organization estimates that annual seasonal influenza epidemics result in three to five million severe cases and 290 000 to 650 000 respiratory deaths worldwide.

The most effective way to prevent seasonal influenza infection is through strain-specific vaccination. How effective the annual influenza vaccines are, depends on a number of factors including the predominantly circulating influenza strains, the obtained vaccination coverage in the (risk) populations and the mutation of the virus compared to previous influenza seasons.

For many decades, only trivalent influenza vaccines (that include two influenza A strains and one influenza B strain) have been available. In recent years, quadrivalent (two influenza A strains and two influenza B strains) have been authorised and are increasingly available. Traditional influenza vaccines have limitations in terms of immune response and the substrate used during manufacturing can reduce overall effectiveness. The newer and enhanced influenza vaccines have been developed, both in trivalent and quadrivalent forms, in an attempt to counteract these limitations.