We've learned so much about the coronavirus in the more than 365 days since our first guide was published.

Dozens of cases and two deaths had been recorded, but as we wrote at the time, little was known about "how destructive the new virus might be." The coronavirus -- and the disease it causes -- hadn't even been named.

There is no better-known virus on Earth than the coronavirus, SARS-CoV-2, which was first detected in Wuhan in December 2019.

In a landslide victory, the coronavirus beats out Ebola, influenza, HIV and the panoply of viruses that cause the common cold for Earth's Most Renowned Virus.

In 2020, 65,000 papers were published and listed on PubMed under the term "coronavirus." A year prior, that number was 885.

The lessons we're learning about SARS-CoV-2 are relevant to this particular virus but also revealing more and more about coronaviruses in general.

During the SARS epidemic, scientists had learned that the spike elicits an immune response, stimulating cells and antibodies to fight the virus.

This gave them a headstart on building vaccines against SARS-CoV-2.

The virus is evolving in a way that may help it evade our immune system, and similar variants seem to be cropping up across the globe -- a development that may affect vaccines.

A majority of the early cases were linked to the market in December 2019, but further investigation revealed COVID-19 infections in people who had no known contact with the market at all.

Traces of SARS-CoV-2 were found, but there was no definitive link between animals in the market and the virus.

A year on, we still don't have a clear answer about the market's role in the pandemic.

Bats are reservoirs of coronavirus -- did this pandemic begin in a bat.

Over 100 million cases have been reported, with COVID-19 infections now found on every continent, including Antarctica.

With only 60 known cases, it seemed SARS-CoV-2 was not highly contagious.

Scientists understood from early on that the virus predominantly spread through the air, moving from person to person via coughing, sneezing and talking.

This idea informed early attempts to slow down the virus, focusing on social distancing, because large droplets do not carry far. .

The debate came to a head in July 2020, when 239 scientists co-signed an invited commentary piece in the journal Clinical Infectious Diseases calling on national and international health and regulatory bodies to "recognize the potential for airborne spread of coronavirus disease 2019." Clashes with the World Health Organization followed.

WHO technical lead Maria Van Kerkhove speaks at a March 11 press briefing on COVID-19, at which WHO Director-General Tedros Adhanom Ghebreyesus announced that the coronavirus outbreak could be characterized as a pandemic. .

Infection via contaminated surfaces was a concern early, with all manner of objects and materials being tested to see how long SARS-CoV-2 would survive on them.

In the most severe cases, patients require mechanical ventilation to assist breathing.

Reports began to surface in March that some coronavirus patients were experiencing anosmia -- a loss of smell.

Although the respiratory tract is where SARS-CoV-2 gets a foothold in the body, the virus has far-reaching and long-lasting effects on the human body?

The most severe cases of COVID-19 are characterized by inflammation.

Some COVID-19 cases see the body's white blood cells produce a lot of cytokines, small proteins that fight infections.

In some patients, blood vessels in the brain are damaged indirectly -- SARS-CoV-2 doesn't necessarily infect brain cells (it may be able to), but the body's overactive immune response can cause the vessels to thin or leak and may result in lasting neurological damage. .

A variety of disparate symptoms seem to stick around long after patients leave the hospital or no longer test positive for the disease.

The long-term prognosis for recovery from a COVID-19 infection will be an intense area of study in 2021 as scientists try to understand how negative effects linger in patients known as "long haulers." Sometimes these symptoms last for weeks, other times they are still with patients eight months later -- the impact will only truly come to light as the year progresses.

The vaccines contain a synthetized strand of mRNA that tells human cells to make spike proteins, similar to those on the surface of SARS-CoV-2.

Having coronavirus vaccines approved for emergency use in less than a year is remarkable.

While two mRNA vaccines, from Pfizer/BioNTech and Moderna, have been approved for use, there are still questions over how long they might provide immunity and whether they can stop disease transmission.

More vaccines are showing promise, too, with the New York Times' tracker currently showing eight in limited or early use

But we've added additional layers of protection as we've learned more about SARS-CoV-2 and its transmissibility

We've learned the best ways to defend against COVID-19, but cases continue to rise in many parts of the world

In our second pandemic year, science will continue to probe and refine the answers to these six fundamental questions