Every year, the flu kills thousands of people and sickens millions more who didn't get a flu shot or in whom it didn't work well. In 1918, the worldwide death toll from flu topped 50 million, and researchers have been worried about a repeat ever since.
Now, a team of current and former government scientists has developed a vaccine that seems – at least in monkeys – to protect against the strains most likely to cause a global pandemic.
The group, which published their monkey results in a study last week, has begun a small trial to test the vaccine in healthy adults.
More than four years ago, the group decided to explore a different way of making a universal flu vaccine, which has been a goal for a generation.
"Maybe we couldn't develop a vaccine that would protect against any flu ever, but could we protect against any flu that has caused a pandemic in people?" asked Dr. Gary Nabel, who has helped lead the work at Sanofi, where he was chief scientific officer.
Influenza viruses mutate much faster than the coronavirus responsible for the COVID-19 pandemic, creating multiple new strains every year. (With the SARS-CoV-2 virus, scientists have been calling them variants, rather than strains, because they're not as different from the original.)
A vaccine designed to combat the flu strains circulating in the Southern Hemisphere's winter might be ineffective by the time the Northern Hemisphere reaches that season, because the circulating strain changes so fast.
But there are parts of the virus that are essential and so remain the same even as it mutates.
Flu viruses, unlike coronaviruses, have a head and a stem. The new vaccine targets where its stem attaches.
In the past, people developing universal flu vaccines started by trying to inactivate the whole live virus, said Nabel, an immunologist and virologist who headed the Vaccine Research Center at the National Institute of Allergy and Infectious Diseases, and is now co-founder, president and CEO of a startup called ModeX Therapeutics.
But he and his colleagues thought they might be more successful by focusing on this key spot. They added a so-called adjuvant to boost the immune system's response to the vaccine.
Their vaccine didn't work very well in mice or ferrets, which are the usual test animals for flu vaccines, but it was quite effective in monkeys, whose immune systems are much more similar to humans'. The monkeys made lots of neutralizing antibodies to a number of dangerous flu strains, the new study showed.
Any vaccine that performs well in monkeys is likely to do well in humans, too, particularly among young children, said Drew Weissman, a professor at the Perelman School of Medicine at the University of Pennsylvania, who is developing a different flu vaccine with the same aim of cross-strain protection.
The challenge, Weissman said, will be to make a vaccine that works well in someone over 60, who has been exposed to the flu and flu vaccines for decades.
"Maybe it's a vaccine we start giving our kids so we prevent influenza in the future," he said. "In the meantime, we'll test it in adults and see if adults who have seen influenza many times make a protective immune response."
It's also unclear how long a broadly acting flu vaccine could be effective. Now, flu vaccines are given annually because strains change so much. But a vaccine aimed at a part of the virus that doesn't change could theoretically provide longer-lived protection, said Weissman, who conducted fundamental research leading to the COVID-19 vaccines from Pfizer-BioNTech and Moderna.
On average, 50,000 Americans die every year of the flu. "It's not a mild disease," Weissman said, so any vaccine that provided broad protection could be useful.
Flu vaccines, though not all that effective at the moment, save lives, Nabel said.
"If it weren't for our current flu vaccines, the flu would probably be as deadly as COVID," Nabel said. "Look at 1918. That's what it told you. But like with COVID, we can do better."
Contact Karen Weintraub at email@example.com.
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This article originally appeared on USA TODAY: Universal flu vaccine: Study suggests protection may be possible