Understanding the Effectiveness of Influenza Vaccines: A Review of Recent Studies

Overview of Influenza Vaccine Effectiveness

A recent study has shown that the vaccine effectiveness (VE) against influenza-A-associated hospitalizations was 35% overall, with a range of 27-43%. Among adults aged 18-64, the VE was 23%, and among those aged 65 and above, it was 41%. The findings highlight the role of vaccination in reducing hospitalization rates, particularly among the older population.

DANFLU-1 Clinical Trial and QIV-HD Vaccine

The DANFLU-1 clinical trial revealed that the QIV-HD vaccine significantly lowers hospitalization rates compared to QIV-SD. The trial involved 12,477 participants, and those who received QIV-HD had only 10 hospitalization events for pneumonia or influenza, compared to those who received QIV-SD with 33 events. Thus, the risk of such hospitalizations was 70% lower with QIV-HD. Despite this, the study's limitations, including sample size, no adjustments for multiple comparisons, and conducting it over a single flu season, require further research to confirm these findings.

Vaccine Effectiveness in Preventing Severe Cases

A study aimed to determine the effectiveness of the influenza vaccine in preventing severe cases of influenza in hospitalised patients during the 2022/23 season. The study found that the vaccine was effective, with a vaccine effectiveness of 40.6%. It was particularly relevant in the 65+ age group and in patients with influenza A, marking a significant reduction in the occurrence of severe cases of influenza.

Comparing HMPV and Influenza Hospitalizations

A study comparing the incidence, seasonality, and clinical characteristics of human metapneumovirus (HMPV) and influenza among adults with acute respiratory illness (ARI) hospitalizations found that HMPV infections accounted for fewer hospitalizations than influenza. However, HMPV-associated ARI hospitalization rates were higher than influenza in older adults, Maori and Pacific people, and those of low socioeconomic status, highlighting a need for vaccine/antiviral development.

Bias in Vaccine Effectiveness Studies

An article discussed the bias in vaccine effectiveness studies of severe disease outcomes due to the inclusion of false cases that are not caused by the infection or disease under study. Defining outcome indicators that minimize the number of false cases rather than the number of missed cases is preferable in vaccine effectiveness studies to avoid underestimating the vaccine's effectiveness.

Maternal Influenza Vaccination and Infant Protection

Maternal influenza vaccination has been associated with a reduction in influenza-associated hospitalizations and ED visits in infants, providing protection until vaccine eligibility for infants at 6 months of age. The importance of maternal influenza vaccination is not just beneficial for the health of the mother but also for the infant.