Mar 27, 2020 09:41 PM

What the Evidence Tells Us About Covid-19

Photo: Pixabay
Photo: Pixabay

Caixin has been reporting on the Covid-19 pandemic since late December, when we first learned that an outbreak of a mysterious respiratory disease in Wuhan had sparked rumors of a return of SARS.

In the three months since, the virus has spread to every continent except Antarctica and reshaped most aspects of our lives, perhaps permanently.

Much about the new disease — labelled Covid-19 by the World Health Organisation (WHO) — is still poorly understood. The coronavirus that causes it is called SARS-CoV-2, and it belongs to the family of viruses responsible for a handful of common colds, as well as the more deadly severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).

Researchers around the world have poured an enormous amount of time and effort into filling the gaps in our knowledge.

Here, Caixin will collect key medical insights as we report on this developing story.

Is there a cure for Covid-19?

No. But not for want of trying.

Right now, doctors mostly provide patients with symptomatic relief and breathing assistance where necessary, and wait for their immune systems to eliminate the virus. But they are also trying a host of drugs. Some were already on the market for other diseases, and some are experimental. Both varieties have strengths and drawbacks, which you can read about here.

AbbVie’s Kaletra was in the former category. The HIV drug was approved by Chinese medical regulators in January to treat Covid-19 and attracted so much interest people began to hoard it. But clinical trials have shown it had little effect on the disease.

Another antiviral drug, Gilead Sciences’ remdesivir, which has not been approved anywhere to treat any disease, has shown more promise but struggled to recruit patients for clinical trials due to strict participation criteria. Trial results are expected soon.

The Chinese government has approved another antiviral, Fujifilm Toyama Chemical's favipiravir, sold as Avigan, saying it is “clearly effective” against coronavirus. But trials are ongoing, and there is concern about its potential to cause birth defects in pregnant women.

Immune-based therapies with synthesized antibodies are another approach, but carry their own risks.

Other approaches include stem cell therapies and administering sick patients with antibodies extracted from the blood of people who have survived the disease. However, both pose logistical issues and are unlikely to be scalable in a way useful to manage a pandemic, experts say.

When will there be a vaccine?

Probably not until the third quarter of 2021.

To inoculate someone against a disease you give them a piece of it — maybe part of its genetic code or one of its proteins — which trains the body’s immune system to neutralize the live virus when exposed to it. Working out what piece to give them and how takes time, but medical advances have shaved that time down considerably.

Mass inoculation would all but neutralize the threat. There have been bold claims of imminent animal tests, human trials and commercialization, some of which have come to fruition.

But population-level vaccine programs are another story. Rushing safety and effectiveness testing risks disaster, experts say. Even after a safe vaccine is developed, it must be produced at scale. And as Caixin reported in February, despite promising innovations in recent years, experts maintain mass vaccinations could be at least 18 months away. Read our feature on the vaccine race here.

What are ‘asymptomatic carriers’?

Asymptomatic infections are one of the mysteries of the new coronavirus.

Early evidence suggests some people may experience no clinical symptoms of Covid-19, even though a laboratory test can find traces of the SARS-CoV-2 virus in their bodily fluids, and that these people may be able to infect others.

The proportion of coronavirus cases that are truly asymptomatic has proved controversial and remains unclear. Research on the subject has failed to follow people throughout the whole course of the disease to see if they were truly symptomless, “pre-symptomatic” and infectious, or just had very mild symptoms.

Evidence suggests all three categories of people can infect others. Experts say what matters is not whether they are technically “asymptomatic,” but whether they may spread the virus undetected, frustrating disease surveillance and control efforts.

A peer-reviewed paper published in Science in mid-March used case data and mathematical modeling to estimate that prior to Jan. 23, unrecorded cases — which are often mild or asymptomatic cases — were responsible for 79% of known infections.

Truly asymptomatic infections are not thought to be major drivers of disease spread, however, according to Li Xingwang, an infectious disease expert at Beijing’s Ditan Hospital, because such people have less of the virus in their bodies and shed less, he said.

Asymptomatic infections have also taken on a political dimension, with Caixin journalists revealing that authorities in Wuhan, the city of 11 million where the epidemic began, were still finding around a dozen new infected people without symptoms each day when they reported the city had zero new “confirmed” cases.

Some countries, like South Korea, include people who test positive for the virus but show no symptoms in their official lists of confirmed cases. The WHO takes the same view.

China, however, does not. The National Health Commission (NHC)’s fourth edition of its Covid-19 diagnostic criteria reiterated that officials should keep a separate tally of asymptomatic cases and exclude them from the public logs of confirmed cases. That practice remains controversial, and complicates the view that China has effectively subdued the spread of the virus. For its part, Chinese health officials say asymptomatic cases are quarantined and added to the confirmed case count if they show symptoms.

How does the disease spread? Is it worth wearing a mask?

The Covid-19 pandemic has raised the question of whether people should wear face masks whenever they venture out in public in order to check the spread of the disease.

In China, where the masks have long been associated with progressive ideas about public health, the answer is a resounding “yes.” But many in other nations aren’t so sure, with some officials questioning the science behind their use and saying mass mask-wearing may spark panic. The division appears to follow geographic lines, with mask-wearing more visible in East and Southeast Asian nations, while donning a mask elsewhere has been known to spark shock or even draw ridicule.

So, how effectively do face masks prevent Covid-19 from spreading?

To answer that question, we need to consider how the disease spreads. The virus gathers in the noses and throats of infected people, who cough and sneeze, “launching” it in droplet form at uninfected people, who inhale it. There’s evidence it can be transmitted by contact with contaminated surfaces, and some evidence it can also spread via “aerosol transmission” when people in closed environments for long periods breathe air containing tiny virus-contaminated particles, or during life-saving medical procedures where breathing tubes are used to rush oxygen into the lungs.

As this in-depth Caixin piece explains, while there is evidence that standard surgical masks can guard against transmission from droplets, their loose-fitting design cannot completely filter out smaller airborne particulates. For that, you need N95 respirators — the domelike, tighter-fitting masks which seal around the nose, that earn their name because they block up to 95% of particles down to 0.3 microns in diameter. Even so, respirators can’t provide total protection, but they do seem to improve one’s chances.

Face masks are best used in combination with other preventative strategies like social distancing and regular handwashing. While Chinese authorities regularly require people to mask up in public spaces, officials in the United States and Europe rarely make the same recommendation.

There’s another reason authorities in some places recommend the general public not use masks: supply. In countries without a large supply of masks, it makes more sense to save them for healthcare workers who will be directly exposed to the SARS-CoV-2 virus daily, as they are the ones who need them most.

Global face-mask supplies — particularly of those made in China — remain far from sufficient despite attempts to ramp up capacity.

Face masks can also stop people from semiconsciously touching their mouths and faces with virus-contaminated hands. That’s important because there’s evidence the virus can survive on surfaces such as plastic and stainless steel for days.

How do you test for Covid-19?

The most common way doctors and nurses test for coronavirus is to take a swab from the nose or throat of a patient and send it to the lab for a nucleic acid test (NAT).

It’s worth noting that a NAT can only identify genetic traces of the SARS-CoV-2 virus, and doesn’t indicate whether the virus is whole, alive, transmissible or causing disease, experts say. It’s something well illustrated by the ongoing mystery of two dogs in Hong Kong that have tested positive for the virus, even though neither showed any indication it was infected with the disease it causes in humans.

But questions over the reliability of NATs, and their potential to record false negatives, have sparked fears many infections were going uncounted — something Chinese officials have vociferously denied.

Coronavirus is generally diagnosed based on a combination of clinical symptoms and lab tests, depending on the conditions, testing availability and the prevalence of the disease in the environment. In mid-February, facing a backlog of cases and long wait times for tests in Hubei, authorities changed the diagnostic criteria for Covid-19 in that province to allow confirmation via chest CT scans without lab tests. The province logged 14,000 new cases overnight under the new criteria, making global headlines. The move appears to have been an attempt to prioritise treatment over diagnosis while hospitals were overrun by Covid-19 cases, and it was reversed in the next round of guidelines.

Countries that have tested aggressively have generally achieved good outcomes. South Korea, for example, has drawn plaudits for its policy of aggressively testing all suspected Covid-19 cases and quarantining people known to have contracted the virus.

But in many other countries, the process has been more chaotic. At the start of the epidemic, hospitals in the disease-stricken Chinese city of Wuhan suffered severe shortages of diagnostic tools, medical staff, and laboratory capacity. As the outbreak spread, health officials in charge of drawing up diagnostic criteria focused narrowly on patients’ contact with the South China Seafood Market at the center of the outbreak, until the number of sickened people with no connection to the market became too big to ignore.

Concerns have also persisted over recovered patients who test positive again. Most experts say it’s highly unlikely people can contract the disease twice in such a short time, and that the phenomenon probably reflects lax hospital discharge criteria or testing failures. But it’s not impossible.

Australian scientists have produced a detailed map of a patient’s immune response to Covid-19, and there is no evidence that being sick with the disease once does not confer immunity to it.

In addition to NATs, doctors in China have been confirming some Covid-19 cases via genetic sequencing, but the technique is costly and not all hospitals have the facilities to conduct it.

Doctors are now also using special tests to find antibodies — substances the body produces to fight an infection which stay in the blood for some time after the patient has recovered. Their presence can tell doctors if someone had the disease, even after they recover. Different antibodies can be detected at different stages of the disease to back up NAT test results.

What are the best quarantine practices?

After squandering opportunities to control the virus in the initial stages of the outbreak, amid unanswered questions about who knew what and when, Chinese authorities moved aggressively to control the spread of the disease by locking down cities, shutting down swathes of the economy, and enforcing mandatory quarantines and travel restrictions nationwide.

Now, as the country tentatively emerges from the worst of its Covid-19 epidemic, some are taking stock of the lessons learned. In an opinion piece for Caixin, editor-in-chief Wang Shuo wrote that while positive nucleic acid tests should be the “gold standard” diagnostic tool for Covid-19, it is also essential to quarantine exposed people whose tests came back negative, as the less-than-total reliability of the testing process means they should still be treated as suspected cases.

The Chinese experience has also shown low-tech “shelter hospitals” of the type deployed in Wuhan allow patients with mild symptoms to receive less intensive forms of care while remaining isolated from other people, thereby reducing hospital infections and concentrating medical resources where they are most needed. Suspected cases should also be kept apart from each other to avoid cross-contamination.

Think we should add something to this story? Contact reporter Flynn Murphy (

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