Five years after COVID appeared, mysteries remain. Here’s what we know

It’s been more than five years since a cluster of people in Wuhan, China, fell sick with an unknown virus that would upend daily life across the world.

The germ didn’t have a name nor did the illness it would cause. It wound up setting off a pandemic that exposed deep inequities in the global health system and reshaped public opinion about how to control deadly emerging viruses.

The virus is still with us, though humanity has built up immunity through vaccinations and infections. It’s less deadly than it was in the pandemic’s early days and it no longer tops the list of leading causes of death – but the virus is evolving, meaning scientists must track it closely.

Five years on from the outset of the COVID-19 pandemic, here’s what we know and what mysteries still remain.

Where did the SARS-CoV-2 virus come from?

We don’t know. Scientists think the most likely scenario is that it circulated in bats, like many coronaviruses.

They think it then infected another species, probably racoon dogs, civet cats, or bamboo rats, which in turn infected humans handling or butchering those animals at a market in Wuhan, where the first human cases appeared in late November 2019.

That’s a known pathway for disease transmission and likely triggered the first epidemic of a similar virus, known as SARS, in the early 2000s.

But this theory has not been proven for the virus that causes COVID-19. Wuhan is home to several research labs involved in collecting and studying coronaviruses, fueling debate over whether the virus instead may have leaked from one.

It’s a difficult scientific puzzle to crack in the best of circumstances. The effort has been made even more challenging by political sniping around the virus’ origins and by what international researchers say are moves by China to withhold evidence that could help.

Earlier this week, the World Health Organization (WHO) called on China to share more data with investigators looking into the pandemic’s origins, calling transparency a “moral and scientific imperative” that will help countries “prevent and prepare for future epidemics and pandemics”.

The true origin of the pandemic may not be known for many years – if ever.

How many people died from COVID-19?

Probably more than 20 million. The WHO has said member countries reported more than seven million deaths from COVID-19, but the true death toll is estimated to be at least three times higher.

Countries in the European region, for example, have reported nearly 2.3 million deaths since early 2020, with 583 deaths reported over the past four weeks.

Older adults are particularly vulnerable, accounting for a greater share of hospitalisations and deaths.

“We cannot talk about COVID in the past, since it’s still with us,” WHO chief Tedros Adhanom Ghebreyesus said.

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What vaccines were made available?

Scientists and vaccine-makers developed COVID-19 vaccines in record time, saving tens of millions of lives worldwide.

Less than a year after China identified the virus, health authorities in the US and the United Kingdom cleared vaccines made by Pfizer and Moderna.

Years of earlier research – including Nobel-winning discoveries that were key to making the new technology work – gave a head start for so-called mRNA vaccines.

Today, there’s also a more traditional vaccine made by Novavax, and some countries have tried additional options.

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Rollout to poorer countries was slow, but the WHO estimates more than 13 billion doses of COVID-19 vaccines have been administered globally since 2021.

The vaccines aren’t perfect. They do a good job of preventing severe disease, hospitalisation, and death, and have proven to be very safe, with only rare serious side effects. But protection against milder infection begins to wane after a few months.

Like flu vaccines, COVID-19 shots must be updated regularly to match the ever-evolving virus – contributing to public frustration at the need for repeated vaccinations.

Efforts to develop next-generation vaccines are underway, such as nasal vaccines that researchers hope might do a better job of blocking infection.

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Which variant is dominating now?

Genetic changes called mutations happen as viruses make copies of themselves, and this virus has proven to be no different.

Scientists named these variants after Greek letters: alpha, beta, gamma, delta, and omicron. Delta, which became dominant in Europe in late June 2021, raised a lot of concerns because it was highly contagious as the first version of the virus.

Then in late November 2021, a new variant came on the scene: omicron.

“It spread very rapidly,” dominating within weeks, said Dr Wesley Long, a pathologist at Houston Methodist Hospital in the US, which saw similar timelines on the new strains.

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“It drove a huge spike in cases compared to anything we had seen previously”.

But on average, the WHO said, omicron caused less severe disease than delta, which scientists believe may be partly because immunity had been building due to vaccination and infections.

“Ever since then, we just sort of keep seeing these different subvariants of omicron accumulating more different mutations,” Long said. “Right now, everything seems to lock on this omicron branch of the tree”.

The omicron variant now dominant in Europe is KP.3, according to the European Centre for Disease Prevention and Control (ECDC). The XEC strain, a merger between KP.3 and another variant, is also being monitored.

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Existing COVID-19 medications and the latest vaccine booster should be effective against the variant, Long said, since “it’s really sort of a remixing of variants already circulating”.

What do we know about long COVID?

Millions of people remain in limbo with a sometimes disabling, often invisible, legacy of the pandemic called long COVID.

It can take several weeks to bounce back after a bout of COVID-19, but some people develop more persistent problems. The symptoms that last at least three months, sometimes for years, include fatigue, cognitive trouble known as “brain fog,” pain, and cardiovascular problems, among others.

Doctors don’t know why only some people get long COVID. It can happen even after a mild case and at any age, although rates have declined since the pandemic’s early years. Studies show vaccination can lower the risk.

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It also isn’t clear what causes long COVID, which complicates the search for treatments.

One important clue: Increasingly researchers are discovering that remnants of the coronavirus can persist in some patients’ bodies long after their initial infection, although that can’t explain all cases.