WASHINGTON (REUTERS) - The following is a summary of some recent studies on Covid-19. They include research that warrants further study to corroborate the findings and that has yet to be certified by peer review.

Omicron infections contagious for at least 6 days

Patients infected with the Omicron variant of Sars-CoV-2 remain contagious for just as long as patients infected with earlier variants, according to a small study.

Researchers took blood samples from 56 newly diagnosed patients, including 37 with Delta variant infections and 19 with Omicron infections. All were mildly ill, such as with flu-like symptoms, but none were hospitalised.

Regardless of which variant or whether or not they had been vaccinated or boosted, study participants "shed live virus for, on average, about six days after symptoms (began), and... about one in four people shed live virus for over eight days", said Dr Amy Barczak of the Massachusetts General Hospital in Boston, who co-authored a report posted on medRxiv ahead of peer review.

Although it is unknown exactly what is the virus load needed to spread the disease to others, the data suggests that "people with mild Covid-19 infection may be contagious on average for six days, and sometimes longer", Dr Barczak said.

"Decisions about isolation and masking should take such information into account, regardless of variant or prior vaccination status," she added.

Takeda angioedema drug shows promise

A drug used to treat a blood vessel condition called angioedema has shown promise as a treatment for Covid-19 in laboratory experiments, researchers said.

Icatibant, sold as Firazyr by Japan's Takeda Pharmaceutical, blocks a protein called bradykinin receptor b2 in the so-called kinin system. The protein is regulated by the ACE2 protein on cell surfaces, which the coronavirus uses as a gateway for infection. When the researchers analysed nasal cells obtained from newly diagnosed Covid-19 patients, they found elevated levels of bradykinin receptor b2, which led them to wonder whether blocking that protein with icatibant could protect the airway-lining cells against the coronavirus.

"To our surprise, icatibant effectively reduced viral load by more than 90 per cent and protected cultured human airway cells from cell death upon Sars-CoV-2-infection," said Dr Adam Chaker of Technical University of Munich, whose team members reported their findings on Saturday (March 5) in the Journal Of Molecular Medicine.

Icatibant uses different biochemical pathways to protect the airways than steroids, the researchers found.

In their test tube experiments, repeated dosing of icatibant did not stop coronavirus infection completely, but reduced the severity of infection, they reported. Previous small observational studies have suggested that icatibant might provide some benefit to Covid-19 patients. Now, Dr Chaker said, it is time for "double-blind, placebo-controlled clinical trials... conducted in high-risk patients and see potential to use icatibant as add-on treatment at early stages of infection".

Heart defects boost risks for hospitalised patients

People born with heart defects who become sick enough from Covid-19 to be hospitalised are at higher risk of becoming critically ill or dying, researchers said.

The findings were drawn from a study that compared 421 patients with a heart defect who were hospitalised for Covid-19 with 235,638 similar hospitalised Covid-19 patients born with normal hearts.

After researchers accounted for patients' other risk factors, those with congenital heart defects were 40 per cent more likely to be admitted to an intensive care unit, 80 per cent more likely to need mechanical ventilation, and two times more to die while hospitalised, compared with patients in the control group, according to the report published on Monday in the journal Circulation.

Hospitalised patients with a congenital heart defect and another health condition faced even higher risks for poor outcomes, the researchers found.

"People with heart defects should be encouraged to receive the Covid-19 vaccines and boosters and to continue to practice additional preventive measures for Covid-19, such as mask wearing and physical distancing," study leader Karrie Downing of the United States' Centres for Disease Control and Prevention said in a statement.