Sharon Lewin, director of The Peter Doherty Institute for Infection and Immunity in Melbourne and a top expert on infectious disease policy, spoke with AFP about the unfolding coronavirus pandemic.Countries that got caught off-guard or did not respond to the outbreak decisively have paid a heavy price, she said. A few got ahead of the curve.Q. What do we most urgently need to know about COVID-19?What level of containment actually makes a difference to block transmission, and when to escalate those interventions. That is still unclear. Do you need to go Wuhan-style to completely stop it? Countries are in different phases right now. Another unanswered question is whether you have long-term immunity if you are exposed. Finally, what is the real mortality rate? There is a lot of confusion around that. Q. So what IS the mortality rate?We think it is, overall, 1 to 2 percent as compared to the number of infections. It goes up with age: over 80, up to 15 percent; 70-79, about 6 percent; 60-69, about 3 percent. Under 60, much, much less. It also rises with certain co-morbidities such as hypertension, cardiovascular disease, diabetes. But the mortality rate is also dependent on healthcare capabilities. Wuhan - where the mortality rate was around 8% to 10% - most likely got hit harder because the virus overwhelmed the healthcare system. They were totally unprepared. Compare that with Chinese provinces outside of Wuhan (the capital of Hubei Province), where the mortality rate dropped to between 1% and 2%. Same virus, same population, a similar age distribution. Conclusion? The difference is related to the severity of the infection when you "present", or take action. Outside of China, there was preparation, though in Italy the situation is alarming - they are reporting mortality rates of about 6% across the board. Italy also has a higher proportion of elderly people than China.Q. If a country does everything right, how much will it help?We don't have the data to answer that. We do know that the mortality is different in different parts of the world, but it is very unlikely to be because there are different strains of the virus. So the key factors appear to be severity of illness and healthcare capability.Italy is an example of the consequences of being very late in recognising the problem. They reacted when they had deaths. When you are at that stage, it means that you have had virus circulating for two or three weeks already. I give full marks to Singapore and Hong Kong, which moved much earlier. From a policy standpoint, that is much, much less acceptable to the public because the threat is hardly visible. But once you have deaths, escalating cases, and people can't get into hospitals, the public cries out for interventions. South Korea has big numbers, but they were highly localised in two communities. It is also significant that Hong Kong and Singapore had SARS, and South Korea had MERS - they know how these things can spread like wildfire. Q. What is the difference in impact between lockdown and 'softer' restrictions, as in the US and Australia? Lockdown works. As soon as Wuhan locked down, two weeks later - exactly the incubation period of the virus - numbers of infections started to decrease. But the question is whether you have to go that far. In Singapore, they tested aggressively very early on and chased down cases through contact tracing. But their social distancing measures were not that extreme. They closed schools, but only for two or three weeks. Meetings were banned but people still went to work.Q. Will the virus bounce back in places where policy interventions have worked?In China, for example, I doubt that there's widespread immunity. You have 80,000 confirmed cases in a population of 1.5 billion. We need to know more about how some people develop immune responses to the virus without any symptoms. Usually viruses burn out when they run out of people to infect. We talk about 'R-zero' - the number of people that each person with the virus infects. The virus will only go away with the R0 is less than 1, which means that not everyone in infecting someone else.Will it come back? We don't know. SARS didn't.The “sudden and near-constant stream of news reports” about a disease outbreak “can cause anyone to feel worried”, @WHO said in new guidance on mental health + #COVID19 . “Get the facts; not the rumours + misinformation”. #coronavirus #MentalHealthhttps://t.co/T0cu6qayTm— UN News (@UN_News_Centre) March 16, 2020 How would you grade China's response, and the US?China was extremely late, and there was obviously a lot of dysfunction in December in January. But they were working with no information, and did a spectacular job of shutdown later on.The US is surprising. The US Centers for Disease Control (CDC) is like the guru of all public health responses, and the US has done spectacular things outside of the US with Ebola, SARS, etc. But in their own backyard, they have nowhere near the success and leadership on coronavirus that the showed in responding to disease in other places. Q. Has the US response been undermined by Trump's leadership?Yes. They have some outstanding people in the CDC, and they should be running the show.