This week's roundup of the latest scientific research on the novel coronavirus and efforts to find treatments and vaccines for COVID-19 suggest that long COVID-19 can develop after "breakthrough" infections in vaccinated people and that obesity is a known risk factor for more severe COVID-19.

Breakthrough infections can lead to long COVID-19

The persistent syndrome of COVID-19 after-effects known as long COVID-19 can develop after "breakthrough" infections in vaccinated people, a new study shows. Researchers at Oxford University in the U.K. reviewed data on nearly 20,000 U.S. COVID-19 patients, half of whom had been vaccinated. Compared to unvaccinated patients, people who were fully vaccinated – and in particular those under age 60 – did have lower risks for death and serious complications such as lung failure, need for mechanical ventilation, ICU admission, life-threatening blood clots, seizures and psychosis. "On the other hand," the research team reported on medRxiv on Tuesday ahead of peer review, "previous vaccination does not appear to protect against several previously documented outcomes of COVID-19 such as long COVID features, arrhythmia, joint pain, Type 2 diabetes, liver disease, sleep disorders, and mood and anxiety disorders." The absence of protection from long COVID-19 "is concerning given the high incidence and burden" of these lasting problems, they added.

Genes may explain critical COVID-19 in young, healthy adults

A gene that helps the coronavirus reproduce itself might contribute to life-threatening COVID-19 in young, otherwise healthy people, new findings suggest. French researchers studied 72 hospitalized COVID-19 patients under age 50, including 47 who were critically ill and 25 with non-critical illness, plus 22 healthy volunteers. None of the patients had any of the chronic conditions known to increase the risk for poor outcomes, such as heart disease or diabetes. Genetic analysis identified five genes that were significantly "upregulated," or more active, in the patients with critical illness, of which the most frequent was a gene called ADAM9. As reported on Tuesday in Science Translational Medicine, the researchers saw the same genetic pattern in a separate group of 154 COVID-19 patients, including 81 who were critically ill. Later, in lab experiments using human lung cells infected with the coronavirus, they found that blocking the activity of the ADAM9 gene made it harder for the virus to make copies of itself. More research is needed, they say, to confirm their findings and to determine whether it would be worthwhile to develop treatments to block ADAM9.

Pregnant women get sub-par benefit from first vaccine dose

Women who get the first dose of a messenger RNA (mRNA) COVID-19 vaccine while pregnant or breastfeeding need the second dose to bring their protective benefit up to normal, according to a new study. Researchers compared immune responses to the mRNA vaccines from Moderna Inc. or Pfizer Inc. and partner BioNTech SE in 84 pregnant women, 31 breastfeeding women and 16 similarly-aged nonpregnant, non-lactating women. After the first shot, everyone developed antibodies against the coronavirus. But antibody levels were lower in women who were pregnant or breastfeeding. Other features of the immune response also lagged in the pregnant and lactating women after the first dose but "caught up" to normal after the second shot. In a report published last week in Science Translational Medicine, the researchers explained that in order for a mother's body to nurture the fetus, "substantial immunological changes occur throughout pregnancy." The new findings suggest that pregnancy alters the immune system's response to the vaccine. Given that pregnant women are highly vulnerable to complications from COVID-19, "there is a critical need" for them to get the second dose on schedule, the researchers said.

Coronavirus found to infect fat cells

Obesity is a known risk factor for more severe COVID-19. One likely reason may be that the virus can infect fat cells, researchers have discovered. In lab experiments and in autopsies of patients who died of COVID-19, they found the virus infects two types of cells found in fat tissue: mature fat cells, called adipocytes, and immune cells called macrophages. "Infection of fat cells led to a marked inflammatory response, consistent with the type of immune response that is seen in severe cases of COVID-19," said Dr. Catherine Blish of Stanford University School of Medicine, whose team reported the findings on bioRxiv on Monday ahead of peer review. "These data suggest that infection of fat tissue and its associated inflammatory response may be one of the reasons why obese individuals do so poorly when infected with SARS-CoV-2," she said.

Flu-vaccinated COVID-19 patients have easier surgeries

COVID-19 patients who require surgery appear to face fewer complications if they have previously been vaccinated against the flu, new data suggest. In a preliminary study that has not yet undergone peer review, researchers analyzed outcomes after various types of surgery on nearly 44,000 COVID-19 patients worldwide, half of whom had received a flu vaccine in the previous six months. In a presentation on Saturday at the annual meeting of the American College of Surgeons, they reported that flu-vaccinated patients had significantly fewer serious blood infections, fewer potentially life-threatening blood clots in their veins, fewer serious wound-healing problems, and fewer heart attacks. The flu vaccine was also linked with lower rates of stroke, pneumonia and death. The study cannot prove that flu vaccines were protective, and "the flu shot is by no means a substitute for COVID-19 vaccination," said study leader Susan Taghioff of the University of Miami Miller School of Medicine in Florida. "We strongly recommend that everyone get both their flu and COVID-19 vaccines this year in accordance with current guidelines."

COVID-19 virus spread largely undetected in early 2020

The virus that causes COVID-19 was circulating undetected in the United States and Europe as early as January 2020 and was becoming widespread well before broad testing was implemented, a new computer model suggests. By March 2020, for every SARS-CoV-2 infection diagnosed in the United States, another 97 to 99 infections went undetected, according to a report published in Nature on Monday. "Transmission is likely to have begun by late January in California and early February in New York state, but possibly up to two weeks earlier in Italy," said coauthor Alessandro Vespignani of Northeastern University in Boston. A shortage of tests, plus narrow criteria for testing, helped the virus to spread undetected, he said. "If testing had been more widespread and not restricted to having a travel history from China, there would have been opportunity for earlier detection and intervention," Vespignani said.