The , according to 5 years of data from approximately 15,000 children in Hong Kong.
CAP53/iStockphoto.com
The vaccine is known to last less than a year, but the findings support the need for more vaccine availability in areas where influenza activity occurs year-round, wrote Shuo Feng, PhD, and Susan S. Chiu, MD, of the University of Hong Kong, and their colleagues.
In a study published in the Lancet Respiratory Medicine, the researchers reviewed how vaccine effectiveness changed over time by analyzing data from children aged 6 months to 17 years admitted to a Hong Kong hospital between 2012 and 2017. The study population involved 15,695 children hospitalized for respiratory infections, including 2,500 who were positive for influenza A or B and 13,195 who were negative. Of these, 6.4% of the positive patients and 11% of the negative patients had been vaccinated; 70% to 80% of the vaccinations occurred before the end of December of a given year.
Overall, the vaccination effectiveness rate was 79% for 0.5 to 2 months after vaccination, then dropped to 60% at 2-4 months, 57% at 4-6 months, and 45% at 6-9 months.
The researchers estimated vaccine effectiveness by three time periods: September to December, January to April, and May to August. Across seasons, vaccine effectiveness for all age groups was 79% for September to December, 67% for January to April, and 43% for May to August.
The study results were strengthened by the inclusion of year-round activity, but limited by several factors including lack of data on patients’ vaccination history and the specifics of each year’s flu virus, and lack of generalizability to an adult population, the researchers said.
However, the findings support data from previous studies on the effectiveness of annual vaccination, with the optimal timing from October to December in Hong Kong, they said. “Improved influenza vaccines are needed to provide year-round protection for children, particularly in subtropical and tropical locations,” they added.
The study was supported by the Health and Medical Research Fund and the Research Grants Council, Hong Kong. The lead authors had no financial conflicts to disclose.
SOURCE: Feng S et al. Lancet Respir Med. 2018;6:925-34.