The U.S. has two vaccines ready should the strain of bird flu circulating in dairy cows begin spreading easily to people, federal health officials said Wednesday. They could begin shipping doses widely within weeks, if needed.
So far, there’s no evidence that H5N1 is spreading person-to-person, although one dairy worker in Texas who worked closely with infected cattle had a mild infection and developed conjunctivitis, or pinkeye, in April.
At a briefing Wednesday, government health officials said they are preparing for a potential scenario of H5N1 jumping from animal to person — or person to person. The virus has taken off in dairy cows, infecting at least 36 herds across nine states, raising concerns that it could acquire mutations that would make it easier to spill over into humans.
Studies “suggest that the vaccines will offer good cross-protection against cattle outbreak viruses,” Demetre Daskalakis, director of the National Center for Immunization and Respiratory Diseases, said on the call Wednesday.
Both of the vaccine candidates are already in the nation’s stockpile in limited quantities, officials said in a previous interview.
The Centers for Disease Control and Prevention also said Wednesday that it is testing blood samples from people previously vaccinated with an influenza vaccine to see if it generates an immune response, although it didn’t say which vaccine.
Dawn O’Connell, assistant secretary for preparedness and response at the Department of Health and Human Services, told NBC News earlier there are hundreds of thousands of prefilled syringes and vials ready to ship, if needed.
“We’ve been investing in a library of antigens to move out as quickly as possible should we begin to see a highly transmissible flu strain circulate,” O’Connell said.
H5N1 doesn’t transmit easily between people, although global health officials remain concerned due to its high mortality rate, which hovers around 50%, according to the World Health Organization.
There are no signs the virus is mutating to be more transmissible between people, officials said Wednesday.
Vivien Dugan, who heads the CDC's influenza division, said that the government would begin looking at vaccination if there were alterations in the virus’s genetic code that would affect its existing countermeasures. It currently has a number of antiviral medications in supply that target influenza viruses, including Tamiflu.
The people needing vaccination — and the number of doses that the U.S. would require — would hinge on how the virus changes and how widespread the outbreak becomes, experts say.
Right now, there are over 100 people, most of whom work with farm animals, being monitored for signs of infection, officials said.
Preparation underway
Should the U.S. need the vaccines, the federal government could ship out “hundreds of thousands of doses” within a few weeks, O’Connell said.
It could have over 100 million doses shipped within three to four months.
Health officials expect that people will need two doses of that vaccine, O’Connell added, meaning 100 million doses is only enough for 50 million people.
Again, given this is a hypothetical, it’s possible the U.S. may not need that many vaccines. But it could also produce more, if needed, O’Connell said.
They are produced using traditional vaccine technology that has been the standard approach to vaccines for decades. However, the process can take months.
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O’Connell said the U.S. is also pursuing a third vaccine based on the same mRNA-technology used in Pfizer’s and Moderna’s Covid vaccines. She added that an mRNA vaccine could be quicker to manufacture because “you can switch in and switch out the genetic sequencing very easily.”
All three vaccines would also need approval from the Food and Drug Administration before they can be distributed across the U.S.
In a statement, the FDA said it is “actively engaged” with other federal health agencies in assessing pandemic influenza vaccine candidates should the need for a vaccine arise.
A number of unknowns
Dr. William Schaffner, an infectious disease expert at the Vanderbilt University Medical Center, said having vaccine candidates on hand is important because it reduces the time needed to get the shots in people’s arms.
During the 2009 H1N1 swine flu pandemic, researchers eventually developed a vaccine to prevent the spread of the virus, but by the time the shots were manufactured and ready to be distributed, the outbreak had already petered out, he said.
“It’s very good that we have reduced the time necessary to create a vaccine by having candidates already available, should they be needed,” he said.
Despite the government having two vaccine candidates, there are still a number of questions, including how much protection the shots would provide against infection and severe illness, said Dr. Judith O’Donnell, director of infection prevention and control at Penn Presbyterian Medical Center in Philadelphia.
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“There’s a lot we don’t know about these candidate vaccines and how they’ll work,” she said.
The U.S. has contracts with three manufacturers for pandemic influenza vaccines: GlaxoSmithKline, CSL Seqirus and Sanofi. One of the vaccine candidates is from CSL Sequirus.
A spokesperson for CSL Seqirus said the company has no data available on vaccine effectiveness because the number of human cases of H5N1 is too low for studies.
However, a phase 2 study testing a vaccine that targets a virus closely related to H5N1 shows that it generates a promising immune response and should “cross-react with the H5N1 viruses currently circulating in cattle in the U.S,” the spokesperson said.
O’Connell said the government has a number of potential adjuvants, substances added to vaccines to boost the immune response, that could be used if needed.
During the pandemic, the virus was typically severe in older adults and people with underlying health conditions. However, the 2009 H1N1 swine flu virus disproportionately affected young people. It’s unclear how this strain of H5N1 would affect people because human infections are rare.
O’Donnell said that given the amount of vaccine skepticism, as well as vaccine fatigue from the pandemic, the government would also likely need to begin a vaccine campaign to persuade people to get vaccinated.
“It’s very disheartening to see so much vaccine skepticism and vaccine fatigue,” she said.
