January: A scientist in China confirms that a mysterious new pneumonia-like illness identified in Wuhan, China, in December 2019, can be transmitted from human to human. Two days later, China puts Wuhan under strict lockdown. Meanwhile, on the other side of the globe, the U.S. sees its first case of the disease, later named COVID-19. The patient is a resident of Washington state who had traveled to Wuhan. The Trump Administration declares a public health emergency.

February: Cases of COVID-19 begin to multiply around the world. Countries are restricting travel to contain the virus.

March: The WHO characterizes COVID-19 as a pandemic. In the U.S., the Grand Princess cruise ship is held at sea off the coast of California after 21 of the 3,500 people aboard test positive for the virus. California also becomes the first state to order all residents to stay home with the exceptions of going to an essential job or shopping for essential needs. As cases grow, hospitals become overwhelmed, and there is a nationwide shortage of personal protective equipment (PPE). In Italy, there is a moment of solidarity when people in quarantine sing from their balconies, starting a trend that sweeps across Europe.

April: As cases continue to surge, countries keep their borders sealed. Businesses shut down (leading to massive job losses), schools close, sporting events cancel, and college students go home. People start wearing masks and practicing “social distancing.”

May: Experts focus on “flattening the curve,” meaning that if you use a graph to map the number of COVID-19 cases over time, you would ideally start to see a flattened line representing a reduction of cases. After months in lockdown, states slowly begin a “phased reopening,” based on criteria outlined by the Trump Administration, in coordination with state, county, and local officials. Meanwhile, scientists across the globe are in a race to understand the disease, find treatments and solutions, and develop vaccines.

June: Efforts to reopen the economy leads to new cases, and the curve is not flattening. Experts point to the dangers of large gatherings and use terms like “clusters” and “super-spreader events.”

July: The pandemic is causing an uptick in mental health issues as job losses continue to soar, parents juggle working at home with caring for or homeschooling children, and young adults grow frustrated by isolation from friends and limited job prospects. Officials debate the best scenarios for allowing children to safely return to school in the fall.

August: The first documented case of reinfection is reported in Hong Kong. On a broader scale, COVID-19 is now the third leading cause of death in the U.S. (after heart disease and cancer).

September: The school year opens with a mix of plans to keep children and teachers safe, ranging from in-person classes to remote schooling to hybrid models. Meanwhile, the WHO recommends steroids to treat severely and critically ill patients, but not to those with mild disease. The Centers for Disease Control and Prevention (CDC) reports that people who had recently tested positive were about twice as likely to have reported dining at a restaurant than were those with negative test results.

October: President Trump tests positive for COVID-19 after a gathering in the White House Rose Garden where multiple people were also thought to have been infected. Meanwhile, the Food and Drug Administration (FDA) grants full approval to a drug called remdesivir for treatment of COVID-19.

November: Cases rise again as cold weather drives more people indoors—the U.S. begins to break records for daily cases/deaths. Many officials around the country bring plans for reopening to a halt. As the holidays approach, the CDC urges Americans to stay home, limit the size of their gatherings, and avoid mixing with people who don’t live in their household.

December: The FDA grants Pfizer-BioNTech the first Emergency Use Authorization (EUA) for an mRNA vaccine, a new type of vaccine that has proven to be highly effective against COVID-19. A week later, it grants another EUA to Moderna, also for an mRNA vaccine. But, as vaccinations begin, major variants of the virus are beginning to circulate. The UK reports that a new variant of the virus, called B.1.1.7, could be more contagious. By the end of the month, B.1.1.7 is detected in the U.S.