Gabriel’s research defined the epidemiology of three novel viral epidemics, namely SARS in 2003, H7N9 influenza in 2013 and most recently COVID-19. As minister, he led Hong Kong government's response against the 2009 influenza pandemic. He was founding co-director of HKU's World Health Organization (WHO) Collaborating Centre for Infectious Disease Epidemiology and Control and founded the Laboratory of Data Discovery for Health (D24H) at the Hong Kong Science and Technology Park.