It's been six months since the World Health Organization (WHO) declared a global health crisis linked to coronavirus. The virus has infected 17 million people on every continent and killed more than 600,000. Ongoing vigilance, social distancing and contact tracing remains key as the virus continues to accelerate and vaccines remain a distant hope. We speak to professor Kanta Subbarao, Director, WHO Collaborating Centre For Reference And Research On Influenza, Melbourne, on the race for a vaccine and the possibility of developing herd immunity.