2 years into the pandemic, what have we learned?

 Before March 2020, many people saw pandemics as a thing of the past. Then came COVID-19. Scientists still do not know exactly where the virus that caused it — SARS-CoV-2 — came from, but it soon reached almost every country worldwide. Over 2 years, the virus has evolved, producing several variants. In this Special Feature, we look at the evolution of SARS-CoV-2 and ask what lessons scientists have learned.

In late 2019, there was a sudden increaseTrusted Source in pneumonia cases in central China. By January 7, scientists had identified and isolated a previously unknown coronavirus, now designated SARS-CoV-2.

On March 11, 2020, the World Health Organization (WHO)Trusted Source declared COVID-19 a pandemic.

Now, 2 years on, authorities have recorded more than 458 million cases of COVID-19, the disease resulting from SARS-CoV-2. The disease has also played a role in the deaths of more than 6 million people.

The first cases

On December 29, 2019, experts linkedTrusted Source four cases of pneumonia of unknown etiologyTrusted Source to the Huanan Seafood Wholesale Market in Wuhan, central China.

On January 7, 2020, researchers isolated the causative agent, SARS-CoV-2, and on January 10, they sequenced its genome.

By January 2, 2020, doctors had confirmed that 41 peopleTrusted Source in a Wuhan hospital with severe respiratory illness had a SARS-CoV-2 infection. Of these individuals, 27 had had exposure to the seafood market.

Other human coronaviruses

Many coronaviruses exist, affecting both animals and people. Most cause infections with mild to moderate symptoms in the upper respiratory tract, such as colds.

In recent years, two coronaviruses — SARS-CoV and MERS-CoVTrusted Source — have caused more severe disease. SARS-CoV, which scientists identified in November 2002, was responsible for severe acute respiratory syndrome (SARS), which emerged in Asia. The Centers for Disease Control and Prevention (CDC)Trusted Source note that of the 8,096 people with a known SARS infection, 774 died. There have been no reported cases since 2004.

Scientists first identified Middle East Respiratory Syndrome (MERS), the disease that MERS-CoV-2 causes, in 2012 in Saudi Arabia. The mortality rate for MERS is high — of every 10 people with the infection, three or fourTrusted Source die. There continue to be occasional, localized outbreaks of this disease.

Both of these coronaviruses caused diseases with high fatality rates, but it was possible to contain the spread before they reached pandemic levels. So, were we ready for the next coronavirus?

The origins of SARS-CoV-2

Experts believe that SARSTrusted Source came from bats and that MERSTrusted Source crossed over to people from camels. However, for SARS-CoV-2, researchers have not all agreed on any of the many existing theories.

At first, people thought that SARS-CoV-2 might have come directly from batsTrusted Source. Scientists discounted that theory, though, as the spike protein on SARS-CoV-2 is very different from that on the coronaviruses present in bats.

Now, researchers think it is likely that the virus originated in bats but had an intermediate host between bats and people. A recent study — which has not yet undergone peer review — suggests that live mammals for sale at the Huanan Seafood Wholesale Market in Wuhan, the epicenter of early cases, might have been the intermediate host.

Another recent study — also yet to undergo peer review — that analyzed the evolution of SARS-CoV-2 suggests that “SARS-CoV-2 emergence likely resulted from multiple zoonotic events.” The researchers do not suggest what the intermediate animal hosts might be.

Alternatively, did SARS-CoV-2 escape from a laboratory in Wuhan, as some media outletsTrusted Source have suggested? The WHOTrusted Source has dismissed this theory as “extremely unlikely.”

So, there is still uncertainty about the origins of SARS-CoV-2. And this may be due, in some measure, to a lack of international cooperation, as Prof. Jonathan Stoye, a virologist at the Francis Crick Institute in London, United Kingdom, told Medical News Today.

In his opinion, “one mistake was to start pointing fingers at China and blaming them for the origin of this virus. I think that, naturally, led to pushback from the Chinese [authorities].”

He added: “I absolutely believe in natural origins [of SARS-CoV-2], but the Chinese [authorities] could have made things easier if they’d opened up their books straightaway. They weren’t going to do that when they were being accused of being responsible [for the virus].”

The rise of variants

For almost a year, the original Wuhan variant of SARS-CoV-2 moved across the globe. Then, in late 2020, the number of COVID-19 cases increased rapidly in South East England, in the United Kingdom.

Researchers discovered that a new variant, which was 50% more transmissibleTrusted Source than the original and had 17 unique mutationsTrusted Source, was responsible. In December 2020, the WHO designated it B.1.1.7, or the Alpha variant.

Scientists have since identified many other variants, but the WHO has only designated five as variants of concern (VOC)Trusted Source. The VOCs and the location of their initial identification areTrusted Source:

• Alpha (B.1.1.7): The U.K., September 2020
• Beta (B.1.351): South Africa, October 2020
• Gamma (P.1): Brazil, December 2020
• Delta (B.1.617.2): India, October 2020
• Omicron (B.1.1.529): Multiple countries, November 2021

Each variant has different features. Some variants are more transmissible than others, and some are more virulent. It is these features that have caused the multiple waves of COVID-19.

Source: Medical News Today