The following is a brief roundup of some of the latest scientific studies on the novel coronavirus and efforts to find treatments and vaccines for Covid-19, the illness caused by the virus.

Symptoms can linger for weeks after mild coronavirus infection

Covid-19 patients not sick enough to be hospitalised are advised to isolate themselves for 14 days, but their symptoms often last much longer, doctors in Atlanta have found. They kept track of 272 non-hospitalised coronavirus patients with follow-up phone calls every 12 to 48 hours for up to 50 days.

Three weeks after initial symptoms emerged, 41 per cent of patients still had cough, 24 per cent had shortness of breath on exertion, 23 per cent still had loss of smell or taste, 23 per cent had sinus congestion, and 20 per cent reported headache.

Diarrhea was less common, but still affected some patients beyond three weeks. In a report posted on Sunday on the preprint server medRxiv, without peer review, the researchers note they lacked such details as whether symptoms waxed and waned, and they depended on patient self reporting, which may be less accurate.

"Patients and healthcare providers should be aware that symptom resolution may be gradual," they said, and frequently last longer than the minimum recommended duration of isolation.

They did not address how contagious patients might be as symptoms linger beyond 14 days.

Lockdowns may have averted millions of deaths

Wide-scale lockdowns, including business and school closures, to reduce Covid-19 transmission in Europe may have averted more than three million deaths on that continent, researchers said on Monday in the journal Nature.

Using computer models to estimate the lockdown impact in 11 nations, British scientists said the draconian steps, introduced mostly in March, had "a substantial effect."

A separate study by US scientists, published alongside the European one, estimated that lockdowns in China, South Korea, Italy, Iran, France and the United States prevented or delayed around 530 million Covid-19 cases.

The authors of the second paper say that while lockdowns "impose large and visible costs on society," the data show "consistent evidence that the policy packages now deployed are achieving large, beneficial, and measurable health outcomes."

Negative coronavirus PCR tests rarely wrong

The most reliable method of diagnosing infections with the new coronavirus is the so-called RT-PCR test of samples obtained by nasopharyngeal swab.

To get a sense of how often the RT-PCR test may be wrong, researchers at two large health systems analysed data from nearly 21,000 people who had tested negative for the coronavirus.

Fewer than 5 per cent came back for a repeat test within a week because symptoms that led to them getting tested had persisted or worsened.

Of this group, just 22 people, or 3.5 per cent, were positive for the coronavirus on the second test.

"These observations suggest that false-negative nasopharyngeal SARS-CoV-2 RT-PCR results do occur, but potentially at a lower frequency than is currently believed," the research team concluded in a paper published on Sunday in Clinical Infectious Diseases.

The researchers point out, however, that without retesting the thousands of people who did not come back a second time, they cannot precisely calculate the test's accuracy.

Inflammatory bowel disease does not increase coronavirus infection risk

People with well-controlled Crohn's disease or ulcerative colitis are no more likely to develop severe Covid-19 than those without these autoimmune disorders, according to a nationwide US study.

The conditions, known collectively as inflammatory bowel disease (IBD), affect more than 3 million people in the United States alone. IBD is often controlled with strong immunosuppressive drugs that could theoretically put patients at higher risk from the new coronavirus.

Small studies have suggested that IBD patients whose disease is under control with these medications do not face higher risks from Covid-19.

The new US study of nearly 200,000 people with IBD appears to confirm that. People with IBD and no evidence of a recent flare-up were not at higher-than-average risk for severe Covid-19, according to a report published on Saturday in the medical journal Gastroenterology.

Further, how well they did if hospitalised, and their risk of coronavirus-related death, was similar to Covid-19 patients without IBD.

The authors of the paper conclude that IBD patients in remission should stay on their immunosuppressive medications and should exercise social distancing principles like the general population.

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