Current flu vaccines effective in reducing disease burden in Hong Kong
A study in Hong Kong recently demonstrated that the currently available quadrivalent and trivalent influenza vaccines are effective in reducing disease burden for both children and adults.
The study, performed from December 2014 to August 2017 in 20 private outpatient clinics with a total of 2,566 patients, showed that the overall vaccine effectiveness (VE) against influenza A and influenza B combined was estimated to be 37.9 percent (95 percent confidence interval [CI], 19.3 to 52.2). [Vaccine 2018, doi: 10.1016/j.vaccine.2018.08.075]
The VE estimates for influenza A(H1N1), A(H3N2), B/Yamagata and B/Victoria were 61.1 percent (95 percent CI, 21.8 to 81.1), 26.4 percent (95 percent CI, -1.32 to 46.6), 67 percent (95 percent CI, 25.9 to 85.3), and 60.4 percent (95 percent CI, 0.3 to 84.3), respectively.
For influenza A(H1N1), the VE was higher for 2016–2017 (64.3 percent; 95 percent CI, -71.3 to 92.5) vs 2015–2016 (59.7 percent; 95 percent CI, 9.8 to 82).
For influenza A(H3N2), the VE was generally higher for 2015–2016 (39.9 percent; 95 percent CI, -50.6 to 76) and 2016–2017 (27.9 percent; 95 percent CI, -11 to 53.2) vs 2014–2015 (18 percent; 95 percent CI, -46.4 to 54).
“The estimates we reported in this study are substantially higher than estimates from China and Israel, but generally comparable with Europe and other countries such as the US, Japan and Canada,” the authors noted.
Age-stratified VE estimates were higher among adults aged 50–64 years (68.5 percent) vs the paediatric age group (35.5 percent to 35.8 percent) or adults younger than 50 years old (38.6 percent). The VE estimate, however, was shown to be markedly lower in patients ≥65 years of age (22.1 percent).
“The probable reason for this is the presence of contributory underlying medical conditions or immunosenescence. This higher risk of complications after influenza infection also warrants special consideration in vaccination strategies when epidemic seasons are anticipated,” the authors explained.
In the territory-wide study, nasal and throat swab samples were collected from patients ≥6 months of age who presented with at least two symptoms of acute respiratory illness (ARI), including fever ≥37.8 °C, cough, sore throat, runny nose, headache, myalgia and phlegm within 72 hours of illness onset.
Among the patients recruited, 43.6 percent tested positive for influenza A/B by polymerase chain reaction (PCR) assay. Patients who tested positive were older and more likely to present with one or more of the symptoms of ARI. More patients in the group received quadrivalent vs trivalent vaccines (54.6 percent vs 19.7 percent).
Influenza vaccine was received by more patients who tested negative for influenza A/B on PCR assay vs those who tested positive (16 percent vs 11.5 percent; p<0.001). This was largely consistent with the local influenza vaccination coverage, with around 700,000 doses administered in a population of 7.3 million in 2017. [http://www.info.gov.hk/gia/general/201706/22/P2017062200297.htm]
Influenza causes an average of 12,700 respiratory hospitalizations and 430 respiratory deaths annually in Hong Kong. [Sci Rep 2017;7:929]