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Depending on the findings of a current study, the frequency of tropical influenza re-vaccination in the elderly may soon change.
The Year End flu season from December to February has just passed, and we are now bracing ourselves for the mid-year one from May to July. This biannual pattern distinguishes influenza in tropical countries such as Singapore from the disease in temperate climates, where infections peak in winter.
Another unique feature of tropical influenza is that the virus spreads all year round. Because the immune system weakens with age, seniors are particularly susceptible to flu infections and potentially life-threatening complications like pneumonia.
Moreover, “influenza vaccination is known to be less effective in the elderly compared to the younger population,” says Dr Barnaby Young, Consultant at Tan Tock Seng Hospital (TTSH)’s Institute of Infectious Diseases and Epidemiology. The Ministry of Health and Health Promotion Board recommend that people, especially those in high-risk groups, get annual flu jabs. But research on how to properly vaccinate against influenza in the tropics has been scant — until now.
In an ongoing study, Dr Young is working to boost seroprotection — protection obtained by vaccination — against tropical influenza in the elderly.
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Dr Young’s study was inspired by the conversations he had with staff of TTSH’s Communicable Disease Centre more than two years ago.
“While talking with them about flu vaccine responses, the idea arose that the vaccine is unlikely to provide year-round seroprotection for the elderly living in tropical regions,” he tells Lifewise.
Following a systematic literature review on the topic, Dr Young developed a research proposal as part of his PhD programme at the Lee Kong Chian School of Medicine, Nanyang Technological University. He secured a National Healthcare Group grant to fund his project. He then recruited volunteers aged 65 years and above from senior activity centres islandwide to take part in a 360-day trial, which commenced in mid-2016.
Under the trial, 200 participants were randomly assigned to two equally-large groups. One group received a licenced, standard-dose trivalent influenza vaccine — which protects against three different strains of the virus — on Day 1 and Day 180 of the trial, with each shot administered ahead of the respective flu season. The other (control) group received the same vaccine on Day 1; but instead of a booster injection, a tetanus–diphtheria–pertussis combination vaccine was given at the halfway mark.
Dr Young opted for a combination vaccine rather than a placebo, as the former would benefit participants while still enabling comparison between the two groups. Blood tests were drawn at five time points — Days 1, 28, 180, 208 and 360 — to gauge participants’ ability to fight the flu virus. Two indicators are key: haemagglutination inhibition (HI) titre, or the concentration of antibodies in the blood; and assessment of cell-mediated immunity, which measures the presence of memory cells in the immune system so as to produce antibodies in the event of future infection.
HI assays were performed by the World Health Organization Collaborating Centre for Reference and Research on Influenza in Melbourne, Australia. Blood samples were also sent to the A*STAR Institute of Molecular and Cell Biology to analyse immunological memory responses.
“The trial will finish in October 2017, by which time participants receiving the six-monthly flu vaccine are expected to display better immunity to the virus than those receiving the yearly vaccine,” says Dr Young. He then plans to test the efficacy of this biannual vaccine against two other, less-commonly used influenza vaccines: a highdose version and one containing an adjuvant (a substance which increases the body’s immune response to the vaccine). The version with the best results will subsequently undergo a large clinical trial to see whether it reduces infection rates in older adults. Ultimately, he aims to prevent influenza in the elderly.
“The study will hopefully change vaccination practices throughout the tropics — including Southeast Asia as well as parts of South America and Africa — and increase flu vaccine uptake, which in Singapore is still low at about 10 per cent of the population.”
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This article was last reviewed on
Tuesday, December 21, 2021
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