Tropical Influenza Control Strategies for the Elderly

Summary

TROPICS1 is a randomized, observer-blind, active comparator-controlled, single-center, Phase IV trial in 200 participants aged ≥65 years. The control group will receive a standard dose licensed trivalent inactivated influenza vaccine at day 1, and an active-comparator (Tetanus-diphtheria-pertussis vaccine) at day 180. Participants in the experimental group will receive the same influenza vaccine at day 1 and day 180. Endpoints are immunological, and include measures of haemagglutination-inhibition (HI) titres, micro-neutralisation titres and cell-mediated immunity at 4 time points after the initial vaccination up to Day 360. The primary hypothesis is that participants receiving an influenza booster at day 180 will achieve superior influenza seroprotection (HI titre ≥1:40) at day 208, compared to controls. The World Health Organization (WHO) estimates the global annual burden from seasonal influenza as 1 billion infections, with 3-5 million severe cases and 300,000-500,000 deaths. The pattern and impact of these infections varies considerably with climate. In temperate countries, influenza epidemics characteristically occur during the cold winter months, while in sub-tropical countries, they coincide with the rainy seasons. Closer to the equator, influenza virus activity is more complex. In Singapore, biannual epidemics are usual, but with continuous transmission year-round. Bi-annual epidemics, tri-annual epidemics and year round virus activity have also been described in other tropical countries, from Indonesia and Malaysia to Peru and Mexico. There is no published data reporting year-round influenza vaccine effectiveness in the elderly from countries with continuous influenza virus activity. Despite numerous studies worldwide exploring the HI antibody response to influenza vaccination, the majority of these do not continue follow up beyond seroconversion (21-28 days). However, of the few available, HI antibody titres declined following influenza vaccination in the elderly, such that within 6-12 months geometric mean titres approached pre-vaccination levels. With biannual epidemics and year-round transmission in tropical regions, year-round seroprotection may be important to reduce influenza infections in this environment. A six-monthly vaccination cycle would correspond with the decline in vaccine-induced seroprotection in the elderly, and the 6-monthly periodicity of outbreaks in Singapore and other tropical countries.

Timeline

Start

2016-05

Primary completion

2017-06

Completion

2017-10

Publications

• Young B, Sadarangani S, Haur SY, Yung CF, Barr I, Connolly J, Chen M, Wilder-Smith A. Semiannual Versus Annual Influenza Vaccination in Older Adults in the Tropics: An Observer-blind, Active-comparator-controlled, Randomized Superiority Trial. Clin Infect Dis. 2019 Jun 18;69(1):121-129. doi: 10.1093/cid/ciy836.
• Young B, Sadarangani S, Yew HS, Yung CF, Leo YS, Chen MI, Wilder-Smith A. The immune response to 6-monthly versus annual standard dose inactivated trivalent influenza vaccination in older people: study protocol for a randomised clinical trial. Trials. 2017 Feb 10;18(1):67. doi: 10.1186/s13063-017-1808-8.

Drugs

Indications