n 5 January 2020, the World Health Organization sent a memo to governments across the world reporting a small cluster of pneumonia-like cases in Wuhan, China. For many countries, the warning was like looking through a fog. Each month, the WHO picks up on average 3000 potential disease signals and chooses 30 to investigate. In early January, global health scientists like myself were trying to assess the outbreak of “Wuhan pneumonia”, as it was then called, with huge gaps in our knowledge and considerable uncertainty: what was the virus or bacterial agent causing this cluster? How did it transmit? What was the case fatality rate? And could it be contained? The pandemic may seem to have gone on forever. As we approach the end of 2020, it is easy to lose sight of how much progress science has made over the past 10 months. Since January, scientists have gained a far better understanding of Covid-19 transmission, and have developed the tools to manage the virus. In fact, while the next four months will be difficult, the promising vaccines, better testing and treatments and greater knowledge we now have about how to control this virus will make the situation far better by March. Scientists have never moved so quickly from sequencing a virus to injecting a potential vaccine into a volunteer’s arm. There are 12 vaccine candidates in phase 3 trials being tested for safety and effectiveness, several of which look extremely promising. After collecting more safety evidence, the next set of challenges will be manufacturing and delivering enough doses, and ensuring people trust and will take the vaccine. The biggest question is one of strategy: will the vaccine be used to eliminate, suppress or mitigate the virus? Countries will take different routes, based on their own Covid situations. But the vaccine is far from the only area of scientific progress. We now understand how this virus spreads – through droplets, small aerosol particles and on surfaces – and that aerosols are probably the most significant transmission route. It spreads largely in indoor, crowded and unventilated settings, and even at a two-metre distance, you can still be infected indoors, as the virus can spread through the air and circulate for hours. Ventilating indoor spaces, wearing face coverings, distancing and getting outside for socialising and exercise are all essential to prevent transmission. Unlike flu, which spreads via similar-sized outbreaks in different places, roughly 10% of individuals infected with Covid are responsible for 80% of new infections. Rather than chasing every case, identifying these “super-spreaders” or “super-spreading” events can help to bring down numbers. We also know that asymptomatic carriers are the achilles heel of outbreak control: people may feel fine yet still be infectious. This is perhaps the hardest challenge of fighting Covid. Catching the disease on the basis of people’s symptoms – the normal way to identify carriers of an infectious disease – will mean missing a percentage of cases. This is why mass testing in the community is important, because it helps us identify as many infectious people as possible, even if they don’t have symptoms. On 10 January, the SARS-CoV-2 genome sequence was shared publicly and the WHO shared interim guidance on lab testing for suspected cases. Although lab testing is a reliable way of identifying carriers, even at low viral doses, it is time- and labour-intensive. Huge advances have been made in testing over the past 10 months, and we now have rapid antigen tests that can give results within 30 minutes for just £3.90 each. The WHO has already acquired 120m of these tests for poorer countries that struggle with lab capacity. Testing is one of the key ways to control this virus. The playbook in east Asian and Pacific countries, which have largely eliminated transmission and dealt quickly with flare-ups, involves testing, tracing and isolation, strict border measures, good voluntary guidance and – sparingly used – lockdowns. In the UK, the government plans to roll out mass, cheap testing in the coming months that will help identify carriers of the virus who then need to be supported to isolate. Using rapid antigen tests, Slovakia tested 3.6 million people within a weekend (almost its entire teen and adult population) and plans to do so again several days later. One limitation of testing is that the incubation period of the virus is long, up to 14 days – so testing people repeatedly will be necessary to pick up those who are infected. We’ve also now got decent antibody tests that can identify whether someone has had Covid recently. These have shown us that the antibody response to Covid lasts about 12 weeks. Seroprevalence, the proportion of people with antibodies, is low across most countries, and even in certain boroughs of New York City where 50%+ antibody prevalence is reported, the epidemic is still accelerating, dashing hopes that “herd immunity” could be achieved once a certain number of people have been infected. This is why it’s so important to reduce transmission now. Some have argued that enforcing lockdown restrictions in the present just means delaying the future death toll, but this ignores the role of scientific progress, and the treatments and vaccines that are becoming available. Now, if you’re admitted to hospital with Covid, you’re much more likely to survive than nine months ago. Every time we stop someone getting infected, it gives them a chance to live into an era where better therapies and treatments are available. Doctors have a far better understanding of Covid-19, which isn’t just a respiratory condition, but a multi-system disease that can affect not only the lungs but also the heart, blood vessels, kidneys and brain. Survival rates among patients are improving, and we now know that earlier access to treatment leads to a much lower fatality rate. We also have treatments such as dexamethasone that improves survival rates for the sickest patients, and research into monoclonal antibody therapy and remdesivir is continuing. Some Covid patients can suffer for months from “long Covid”, which seems to be an autoimmune-like condition. The next step is for research into potential treatments and rehabilitation for survivors. The ultimate exit strategy from this pandemic will involve a safe and effective vaccine, treatments for those who have Covid-19, and cheap mass testing. We already have some of these tools, with more expected in the coming months. Although winter will be challenging, with shorter, darker days, colder weather and an overstretched health service, the progress of science means we will have a window of opportunity to break this destructive cycle of lockdowns in the spring. That should give us all cause for hope and optimism. • Professor Devi Sridhar is chair of global public health at the University of Edinburgh