This week's roundup of some of the latest scientific studies on the coronavirus and efforts to find vaccines for COVID-19 reevaluates the benefits of convalescent plasma therapy as a method in treatment while uncovering unexpected damage to the brain in the elderly and the reproductive system of males.

Plasma showing no benefit in severe cases

Blood plasma from COVID-19 survivors was of little benefit to patients with severe COVID-19 pneumonia, researchers in Argentina reported in The New England Journal of Medicine.

So-called convalescent plasma, which delivers the antibodies of COVID-19 survivors to infected people, did not improve critically ill patients' health status or reduce their risk of dying from the disease any better than a placebo.

Researchers randomly assigned 333 hospitalized patients with severe COVID-19 pneumonia to receive convalescent plasma or a placebo. After 30 days, they saw no significant differences in patients' symptoms or health. Mortality rates were nearly the same: 11% in the convalescent plasma group and 11.4% in the placebo group, a difference not deemed statistically significant.

It is still possible that convalescent plasma might help less-sick patients who get the treatment earlier in their illness, said study leader Dr. Ventura Simonovich of the Hospital Italiano de Buenos Aires.

A separate randomized trial from Argentina, posted on medRxiv ahead of peer review, found that when elderly COVID-19 patients received convalescent plasma within 72 hours after their symptoms began instead of a placebo, they were significantly less likely to become severely ill.

COVID-19 may hurt male fertility

Evidence of testicular damage from COVID-19 has been accumulating in a series of small autopsy studies, suggesting that the new coronavirus could have an impact on male fertility.

Researchers from the University of Miami in Florida compared testis tissues from six men who died of COVID-19 and three who died of other causes. Three of the COVID-19 patients had testis damage that would impair their ability to produce sperm.

A Chinese research team made similar observations earlier this year and also found that some COVID-19 patients' immune systems "attacked" the testes, causing severe inflammation, or orchitis.

A separate Chinese team found "significant damage" to the basic cellular tissue of the testicles in 12 men who died of COVID-19.

"The possibility that COVID-19 damages the testes and impacts fertility ... warrants gonadal function evaluation in men infected with COVID-19, or who have recovered from COVID-19, and desire fertility," the Miami team concluded in a report published in the World Journal of Men's Health.

Mutations don't mean faster spread

The coronavirus is picking up genetic changes as it spreads around the world, but the mutations currently documented do not appear to help it spread faster, scientists said in the journal Nature Communications.

Using a global dataset of virus genomes from 46,723 people with COVID-19 from 99 countries, researchers identified more than 12,700 mutations in the genetic material of the virus. Of those, the scientists focused on 185 mutations that they found had occurred at least three times independently during the course of the pandemic.

"Fortunately, we found that none of these mutations are making COVID-19 spread more rapidly," said co-author Lucy van Dorp of University College London's Genetics Institute. Other experts, however, have suggested that one mutation, known as D614G, did increase the transmissibility of the virus.

Francois Balloux, a UCL professor who worked on the study, said that its findings, for now, posed no threat to COVID-19 vaccine efficacy.

"The virus may well acquire vaccine-escape mutations in the future, but we're confident we'll be able to flag them up promptly, which would allow updating the vaccines in time if required," he said.

Delirium may signal COVID-19 in elderly

Delirium is common among older patients with COVID-19 and may be their only symptom, U.S. researchers warned in JAMA Network Open.

Among more than 800 COVID-19 patients over age 65 who showed up at emergency departments around the country, nearly 30% had delirium, they found. Overall, delirium was the sixth most common of all the symptoms and signs in these older patients.

Those most at risk for delirium included elders with vision or hearing impairment, stroke, Parkinson's disease and residents of assisted living or skilled nursing facilities.

Delirium is not on any official list of COVID-19 signs and symptoms, but the U.S. Centers for Disease Control and Prevention (CDC) should add it, said co-author Dr. Maura Kennedy of Massachusetts General Hospital in Boston.

"Sometimes delirium is the chief complaint when these patients arrive at the emergency department," Kennedy said.

"But there can be a number of reasons they come, including falls that occurred because of the delirium. They may present without what we consider typical COVID-19 symptoms, such as fever, shortness of breath and cough," she said.