From the Guidelines
The high incidence of influenza cases during the 2023-2024 season is primarily attributed to the decreased vaccination coverage, with only 53.9% of children 6 months to 17 years of age being vaccinated, as reported by 1. This decrease in vaccination coverage, combined with the waning population immunity due to reduced exposure to influenza viruses during the COVID-19 pandemic years, has contributed to the increased spread of the virus. The 2023-2024 season has also seen multiple circulating influenza strains, including influenza A (H1N1 and H3N2) and influenza B, which can infect different segments of the population, as noted in 1 and 1. Key factors contributing to the high incidence of influenza cases include:
- Reduced vaccination coverage, particularly among non-Hispanic Black children and those residing in rural areas, as reported by 1
- Waning population immunity due to reduced exposure to influenza viruses during the COVID-19 pandemic years
- Multiple circulating influenza strains, including influenza A (H1N1 and H3N2) and influenza B
- Weather patterns and seasonal changes that favor virus transmission, such as cold, dry conditions To mitigate the spread of influenza, annual flu vaccination is recommended for everyone 6 months and older, ideally by October but beneficial anytime during flu season, as recommended by 1. Additional measures to reduce transmission include:
- Good hygiene practices like frequent handwashing, covering coughs and sneezes, and staying home when sick
- Considering antiviral medications like oseltamivir (Tamiflu) for those experiencing flu symptoms, which work best when started within 48 hours of symptom onset, as noted in 1 and 1.
From the Research
Influenza Season 2023-2024
The high incidence of influenza cases during the 2023-2024 season can be attributed to several factors, including:
- Low vaccination rates among certain populations, such as younger adults and those without health insurance 2
- Variations in vaccine effectiveness against different influenza strains, with moderate effectiveness against influenza A/H1N1 and low effectiveness against influenza A/H3N2 3
- Factors influencing vaccination uptake, such as household income, education level, and living state 4
Vaccination Coverage
Vaccination coverage varies by jurisdiction and demographic characteristics, with lower coverage among:
- Younger adults 2
- Those without health insurance 2
- Elderly individuals in certain regions, such as Shanghai, China 4
- Adults and elderly individuals with lower household income, lower education level, and self-rated good health 4
Vaccine Effectiveness
The effectiveness of influenza vaccination in preventing confirmed influenza cases and hospitalizations has been estimated to be:
- 43% overall 3
- 61% in people younger than 65 years old 3
- 35% in older people 3
- 48% against influenza A/H1N1 3
- 15% against influenza A/H3N2 3
Factors Associated with Vaccination Uptake
Factors significantly associated with vaccination uptake include: