June 23 (Reuters) - The following is a 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. Prostate cancer drug improves COVID-19 survival in trial An experimental prostate cancer drug improved the survival of hospitalized COVID-19 patients in Brazil in a clinical trial, researchers reported on Tuesday on medRxiv ahead of peer review. The drug, proxalutamide being developed by Kintor Pharmaceuticals (9939.HK), blocks the effects of androgen hormones by inactivating their "receptors" on cell surfaces. Before the spikes on the surface of the coronavirus can break into cells and infect them, they must be "primed" by a protein called TMPRSS2, which is regulated by androgen receptors, explained study co-author John McCoy of Applied Biology Inc. In the Brazil trial, 645 hospitalized COVID-19 patients who were breathing on their own received either proxalutamide for 14 days or a placebo, plus standard care. After two weeks, recovery rates were 81.4% for the proxalutamide group versus 35.7% for those who got a placebo. After four weeks, 49.4% in the placebo group had died, versus 11% with proxalutamide. Benefits were similar across genders, even though women might not be expected to respond to drugs that block male hormones, McCoy said. The study was done during a COVID-19 surge in a Brazilian state where the Gamma variant, formerly known as P1 and first discovered in Brazil, was dominant. The mortality reduction could be even higher in other settings where infection rates are lower and that variant is not predominant, said coauthor Dr. Carlos Gustavo Wambier of the Alpert Medical School of Brown University. "We still don"t know," he said. "Someone has to initiate an investigation there." (https://bit.ly/3j6WGmX) Mildly ill young COVID-19 patients report lasting symptoms More than half of young adults with mild COVID-19 who self-isolated at home were still reporting troublesome after-effects six months later, a study from Norway published on Wednesday in Nature Medicine found. The study included 312 COVID-19 survivors over age 16, with illnesses of varying severity. Overall, at six months, 189 patients, or 61%, reported persistent symptoms. Of the 61 patients between the ages of 16 and 30 who had only been mildly ill, 32 (52%) continued to have symptoms at six months, including loss of taste and smell (28%), fatigue (21%), trouble breathing (13%), impaired cognition (13%) and memory problems (11%). The researchers said their patients" high rate of persistent fatigue "is striking" and appears higher than what is usually seen after other common viral infections, such as influenza, mononucleosis and dengue. "Considering the millions of young people infected during the ongoing pandemic," they conclude, the findings should prompt "population-wide mass vaccination" and other infection control measures. (https://go.nature.com/3xL7VFF) Worrisome Delta variant becoming dominant in U.S. The highly transmissible coronavirus variants first identified in India and Brazil, now known as Delta and Gamma, respectively, are quickly displacing the Alpha (UK) variant as the most common in the United States, according to a large new study of positive COVID-19 tests from across the country. The percentage of COVID-19 cases due to Alpha dropped from 70% in mid-April 2021 to 42% just 6 weeks later, researchers from Helix, a California-based genomics company, reported in a paper posted on Monday on medRxiv ahead of peer review. The Gamma and Delta variants were "the primary drivers for this displacement," the researchers said. The growth rate of Delta is higher than that of Gamma and is particularly high in counties with vaccination rates below 28.5%, they found. Delta has been widely reported to be even more transmissible than Alpha and to cause more severe disease and hospitalizations. "The expectation is that (Delta) will soon be the dominant variant in the United States," the authors said. (https://bit.ly/3x45vBW) Open https://tmsnrt.rs/3c7R3Bl in an external browser for a Reuters graphic on vaccines in development.