If bird flu spreads to people, existing vaccines may be inadequate
Both wild birds and flocks of poultry continue to die from the highly pathogenic avian influenza, which began spreading globally in 2020. Nearly 59 million farmed birds have been killed in the United States.
It is that The largest outbreak of this type of bird flu, known as H5N1since it was first identified in China in 1996.
The spread of the virus and the high mortality rate have raised questions about two types of possible vaccines: those for birds and those for humans. H5N1 kills nearly all birds it infects; Cases in humans reported since 2003 include the The mortality rate was 56%..
The US Department of Agriculture announced In April, the company announced that it had begun testing several vaccine candidates for poultry.
Human vaccines, on the other hand, would only be considered if the virus eventually undergoes a complicated series of mutations that allow it to spread from person to person. There is no evidence of this yet. The US recorded it human case only of H5N1 last April – the person involved in the killing of poultry with suspected infections in Colorado. The UK reported Two cases on Tuesday, both poultry workers with asymptomatic infections identified by routine testing. Chile reported one infection in March and Ecuador one case in January.
However, scientists have long believed that H5N1 has pandemic potential. In the event of such a crisis, the US has a stockpile of H5N1 flu shots. However, three experts said these would likely prove insufficient if this particular strain of bird flu started to infect humans. The vaccines were only given in trials and were from strains circulating in 2004 and 2005.
“One would expect that these vaccines, based on these older strains, would probably offer little protection against what’s in circulation today,” said Scott Hensley, a professor of microbiology at the University of Pennsylvania.
However, developing new, more tailored vaccines for the current strain would be complicated because most influenza vaccines are cultured in chicken eggs — “a slow process fraught with production problems,” according to Dr. Gregory Poland, founder and director of the clinic’s Mayo vaccine research group. The process requires the individual inoculation of each egg with a modified virus and is of course dependent on a sufficient supply of healthy chickens.
“In a true pandemic situation, the poultry are at risk and then the supply of eggs is severely impacted,” said Dr. Suresh Mittal, virology professor at Purdue University. However, the US does have a supply of chickens to ensure that influenza vaccines can continue to be manufactured.
Better options may emerge. Vaccine researchers are developing vaccines that could be updated to combat any mutant H5N1 strain that might one day take hold in humans. However, no human trials are underway.
“What we need is a library of ready-to-go H5N1 vaccine candidates,” Poland said, adding, “We are putting people and the economy at catastrophic risk if we are not prepared.”
Preparing to spread to humans
In general, scientists are concerned that avian flu could spread to humans through mammalian-to-mammalian transmission, Hensley said. Scientists saw evidence of this during one October outbreak in mink in Spain.
“We fear that such events will result in a mutant form of this virus that could be transmitted among humans,” Hensley said.
Since arriving in the United States last January, avian influenza has spread from birds to others several other mammals: Mountain lions, bobcats, bears, seals, red foxes, coyotes, raccoons, skunks and possums as well as an otter and a bottlenose dolphin.
Poland likened these infections to “the rumble before an earthquake”.
He suspected that an avian flu pandemic would most likely start as a small outbreak among poultry or pig workers, since pigs can transmit the virus from birds to humans. Such an outbreak may or may not be contained immediately, he said.
So the vaccine researchers are preparing. Moderna said it expects to begin clinical testing of an mRNA vaccine called 2.3.4.4b, specific to the strain currently circulating in birds, later this year. mRNA technology offers an advantage because it enables rapid production and updating of vaccines. As experts believe that a future avian flu pandemic will be caused by an H5N1 strain that has not yet evolved, the ideal vaccines could easily be modified to target this virus.
Hensley is leading a research team testing another mRNA vaccine against 2.3.4.4b. Data published in Aprilwhich has not been peer-reviewed, showed that it elicited an immune response in mice and ferrets.
“If we make a vaccine that’s similar to what’s circulating right now, it increases the likelihood that we’ll have cross-protection against something that’s slightly different but very related,” Polen said.
Meanwhile, two other pharmaceutical companies, CSL Seqirus and GSK, have entered into a partnership with the US government Production of experimental vaccine doses which also correspond more to the current variety. GSK’s trial is set to begin later this year, but the company didn’t specify the type of technology it would use. CSL Seqirus said a phase 2 trial evaluating the safety and immune response of an inactivated viral vaccine is scheduled to begin in June.
Mittal said a universal flu vaccine that targets a variety of flu strains could also provide cross-protection against any version of avian flu that one day makes its way to humans. Several such vaccines are currently being developed, but none are at an advanced stage of testing. The National Institutes of Health announced this month that it has started testing a universal mRNA flu vaccine on 50 volunteers.
Could the older vaccines be updated?
The Department of Health and Human Services declined to disclose the quantity or manufacturer of the bird flu vaccine products in the national stockpile. However, NBC News confirmed that three approved H5N1 vaccines were in stock, two of which were made from eggs.
One of these syringes from the pharmaceutical company Sanofi was approved for use in adults in 2007. In a test with around 100 people, two cans released a… protective immune response according to the Food and Drug Administration in 45% of recipients. Since 2007 the US had this stockpiled enough of this vaccine for 6 million people.
When tested against strains circulating in 2016 and 2017, the vaccine elicited a moderate antibody response, according to a Study 2019.
However, the dose is 90 micrograms – much more than the seasonal flu vaccine. In a pandemic situation, that could make it difficult to quickly produce vaccines for everyone who needs them, Poland said.
“For one dose of this H5N1 vaccine, you have to make the equivalent of six normal doses,” he said. “These become real numbers when you’re talking about tens or hundreds of millions of people.”
The FDA approved a second adult vaccine in 2013, manufactured by a GSK subsidiary, to increase supplies. The company called In 2006, two doses elicited a strong immune response in 80% of recipients.
A GSK spokesman said the company won deals last year with the US, Canada, the European Union and the World Health Organization to supply its vaccine in the event of a flu pandemic. Under those agreements, the spokesman said, the company could make at least 200 million doses available to governments around the world.
CSL Seqirus’ third in-stock vaccine was approved in 2020 for recipients 6 months and older. It is grown in cultured cells instead of eggs.
The company said the US has stockpiled millions of doses of antigen – the ingredient in the vaccine that stimulates an immune response – that targets a wide range of strains. In the event of an avian flu pandemic, any antigens found to be cross-reactive with circulating strains could be canned, it said.
The company added that it could produce 150 million doses in six months.
But Poland said even those pledges from manufacturers would still fall short of those made by the Biden administration National Biodefense StrategyThe goal is to produce enough vaccine for the entire United States within about four months of the outbreak of a future pandemic.
