This week's roundup of some of the latest scientific studies on the coronavirus and efforts to find treatments and vaccines for COVID-19 reveals a possible way the virus may have traveled further distances and one daily practice that may help curb the virus load in the infected.

Wildfire smoke likely helped to spread COVID-19

Large wildfires may be linked to increases in COVID-19 cases and deaths in the San Francisco area, according to a paper in the European Review for Medical and Pharmacological Sciences.

Researchers found that between March and September, increases in smoke particles, other wildfire pollutants and carbon monoxide levels corresponded to increases in daily COVID-19 diagnoses and total COVID-19 deaths. While correlation does not necessarily mean causality, coauthor Sultan Ayoub Meo of King Saud University in Saudi Arabia said air pollution provides a means for viruses to move around the environment.

These tiny pollution particles, along with the microorganisms they carry, "can easily be inhaled deep into the lungs and cause infections," Meo said.

"Carbon monoxide is a highly toxic gas which can damage our lungs, resulting as a triggering factor for an increase in COVID-19 cases and deaths in the wildfire region," he told Reuters.

Antiviral mouthwash could help curb coronavirus transmission

Mouthwashes with antiviral ingredients could help decrease COVID-19 transmission by reducing viral loads in the mouths of infected patients when they cough, sneeze or speak, according to a paper in the Journal of Dental Research published on Thursday.

Studies have found that rinses containing cetylpyridinium chloride or povidone-iodine can reduce the oral coronavirus load; other promising compounds include hydrogen peroxide, chlorhexidine, cyclodextrin, Citrox, and certain essential oils.

Coauthor Dr. Florence Carrouel of University Claude Bernard Lyon in France told Reuters everyone should be using these mouthwashes because people can be infected and not realize it.

While more studies are needed to determine appropriate regimens, she suggests using three doses of antiviral mouthwash the day before a meeting and one dose the morning of the event. COVID-19 patients should be using mouthwash regularly for seven to 10 days.

Common-cold antibodies may hijack body's COVID-19 response

A phenomenon called "antigenic sin" may explain why some COVID-19 patients become critically ill, researchers say. Because the new virus shares some features with coronaviruses that cause common colds, the body's immune response can include antibodies that previously learned to recognize and attack those older viruses. This can in turn detract from the body's ability to fight COVID-19 because the common cold antibodies do not reliably attack the new virus.

In severely ill COVID-19 patients, the immune response directed at other coronaviruses is higher than in mildly ill patients, researchers reported on medRxiv ahead of peer review. This situation – when the body reacts to a new invader based on its "memory" of previous invaders – has been seen before and is called "original antigenic sin."

New vaccines must be able to prompt an immune response against this new virus, not merely boost immune responses toward common cold viruses, said coauthor Gijsbert van Nierop of Erasmus Medical Center in the Netherlands told Reuters.

Powerful bowel-disease drugs appear safe during pandemic

People with inflammatory bowel disease (IBD) do not increase their risk for COVID-19 by taking immunosuppressive drugs to control their symptoms, according to a study of more than 5,300 patients with Crohn's disease or ulcerative colitis published on Thursday in the medical journal Inflammatory Bowel Diseases.

"After weighing other known risk factors for COVID-19, including age, race, and other medical issues, we found that immunosuppressive therapy was not associated with an increased risk of COVID-19," coauthor Dr. Kristin Burke of Massachusetts General Hospital and Harvard Medical School told Reuters.

"Amongst the people with IBD that got COVID-19, we also found that use of immunosuppressive medications did not increase the risk of getting severe disease, which we defined as a disease requiring hospitalization, intensive care unit stay, or death."

As other studies have shown, however, older age and obesity were risk factors for severe COVID-19 in these patients, too.