This week's roundup of some of the latest scientific studies on the novel coronavirus and efforts to find treatments and vaccines for COVID-19 reveals new damage caused by the coronavirus, put to rest conspiracy theories about mosquitoes and axes hope for a treatment touted revolutionary in the early days of the pandemic.
Damage to immune cells in bone marrow detected
Even bone marrow may not be a safe harbor from the ravages of COVID-19, according to a study that found previously unrecognized changes in newly produced immune cells, called monocytes, released into the blood from bone marrow.
To learn more about how the body responds to COVID-19, researchers obtained serial "snapshots" of patients' immune health by analyzing their immune cells at multiple points during their hospital stays. In COVID-19 patients with more severe disease, the monocytes do not function properly, researchers reported last week in Science Immunology.
It was not yet clear whether the monocytes are being released from the bone marrow in an altered state or whether the alterations happen after monocytes enter the blood, co-author Tracy Hussell of the University of Manchester in the U.K. told Reuters. Either way, she said, treatments that prevent their release from the bone marrow may help reduce the exaggerated immune response that contributes to poor outcomes in patients with severe COVID-19.
Mosquitoes cannot transmit COVID-19
A mosquito that bites a person with COVID-19 cannot pass the coronavirus infection to its next victim, according to a study by researchers from the U.S. Department of Agriculture and Kansas State University.
Mosquitoes are notorious disease carriers, transmitting West Nile virus, Zika and many other viruses from person to person and among animals. In laboratory experiments, researchers allowed several species of disease-carrying mosquitoes, plus some other biting insects, to feed on blood spiked with the coronavirus, SARS-CoV-2.
The virus was unable to survive and replicate itself in any of the insects, they reported in a paper posted on bioRxiv ahead of peer review.
"Biting insects do not pose a risk for transmission of SARS-CoV-2 to humans or animals," the researchers said. Previous research has found the same result.
Reinfections occur but remain rare
Another case of reinfection after recovery from COVID-19 has been reported, this time in a healthy young military health care provider at a U.S. Department of Defense hospital in Virginia. He was first infected by a patient in March. He recovered within 10 days and "returned ... to excellent health," his doctors reported in Clinical Infectious Diseases.
Fifty-one days later, he was reinfected by a household member. Genetic studies showed the first and second infections to be from slightly different strains of the virus. The reinfection made him sicker, perhaps because the second strain was more potent, or the household contact infected him with a higher load of virus, doctors said.
It was also possible antibodies from the first infection may have triggered his immune system to respond more strongly to the virus the second time his body encountered it. COVID-19 reinfections are still rare, they said.
Kristian Anderson, professor of immunology and microbiology at Scripps Research in La Jolla, California, said virus reinfections are always possible.
"We don't know at what frequency reinfections (with the coronavirus) occur and how that might change over time," Anderson said. Without further studies, "we can't conclude what a single case of reinfection means for longevity and robustness of COVID-19 immunity and relevance for a future vaccine," she added.
Hydroxychloroquine fails to prevent COVID-19
A malaria drug taken by U.S. President Donald Trump to prevent COVID-19 did not help prevent coronavirus infections in health care workers in a gold-standard randomized controlled trial conducted at the University of Pennsylvania.
The new research, published in JAMA Internal Medicine, shows that routine use of the drug, hydroxychloroquine, cannot be recommended to health care workers for prevention of COVID-19, researchers said.
The study largely confirms results from a similar trial conducted at the University of Minnesota in which hydroxychloroquine failed to prevent infection among people exposed to the new coronavirus.
Trump's positive COVID-19 results from Oct. 2 also serves as confirmation that the drug does not provide effective protection against the coronavirus. The White House had confirmed in May that the U.S. president was taking the drug as a precaution despite warnings of side effects by federal regulators.