Jan. 8 (UPI) -- Researchers believe they are one step closer to a "universal" flu vaccine, even as concerns over the seasonal virus move to the back burner during the COVID-19 pandemic.
T cells found in the lungs may hold the key to long-lasting immunity against influenza A, the more common and often more severe form of the virus, according to the researchers behind a study published Friday by Science Immunology.
These cells, which the researchers call resident helper T cells, help the body initiate antiviral responses against new influenza strains even after experience with only one type of the virus, the researchers said.
This type of "generalized" immune response, against all virus strains, is not possible with the currently available yearly vaccine formulations, they said.
The findings come at a time when the winter flu season has been much quieter than normal across the United States.
Only six states -- Arizona, Georgia, Mississippi, Nevada, Oklahoma and South Carolina -- are reporting "low" flu activity, according to data released Friday by the U.S. Centers for Disease Control and Prevention.
The rest of country is reporting "minimal" flu-related activity at this time, as 0.1% of all throat and nasal samples tested come back positive for the seasonal virus, the agency said.
However, the World Health Organization has asked countries to remain on alert for outbreaks of the so-called "bird flu," which usually involves a strain of influenza A, particularly in light of ongoing outbreaks in India.
"T helper cells could be an interesting starting point for longer-lasting flu vaccinations," David Schreiner, co-author of the Science Immunology study, said in a statement.
It might be possible to supplement annual flu vaccines with drugs that promote the formation of these T helper cells, said Schreiner, a professor of biomedicine at the University of Basel in Switzerland.
Using mice infected with influenza A, he and his colleagues found that resident helper T cells remain in the lungs for a long time after a bout of the flu.
One type of these cells releases substances to equip other immune cells with deadlier "weapons" in the fight against the virus if it returns, the researchers said.
Another type assists in the production of antibodies, or cells created by the immune system to fight off viruses, in the lungs, they said.
Vaccines designed to stimulate the production of these cells in the lungs could be effective against multiple strains of the flu, according to the researchers.
"It makes sense that the body keeps a reservoir of these cells in the tissues affected by the infection, where the same or similar pathogens could invade again," study co-author Nivedya Swarnalekha, a doctoral student at the University of Basel, said in a statement.
Since the end of September, clinical and public health laboratories across the country have tested more than 500,000 throat and nasal samples for seasonal influenza, the CDC reported Friday.
Just over 1,000 of them have tested positive for the virus, with about 40% of them involving strains of influenza A, the agency said.
Less than 2% of all doctor and hospital visits across the country through Jan. 2 were related to the flu, the CDC estimates.