100 million vaccine doses could be shipped in a few months

“These (vaccine candidate viruses) are like seeds that are kept in reserve in case there is an outbreak of that particular strain,” said David Diemert, MD, professor of medicine at the School of Medicine and Health Sciences. George Washington University. and director of the GW Vaccine Research Unit.

If bird flu began to spread easily among people, “(the vaccine candidate virus) could be sent to manufacturers to produce millions of doses of vaccine,” he said, “using the existing chicken egg technology we normally use.” for the regular seasonal vaccine. “

TO vaccine candidate virus It is an attenuated or weakened version of the virus. As a result, it is unlikely to cause active infections in people who receive the vaccine.

This type of weakened virus can grow well in chicken eggs, which is what most manufacturers use to produce the seasonal flu vaccine.

The vaccine candidate would also have the surface proteins, known as hemagglutinin, of the virus circulating in the community. This allows a vaccine to generate a protective immune response.

The US National Prepandemic Influenza Vaccine Stockpile (NPIVS) has four types of virus candidates for the H5N1 vaccine, STAT News reported. The bird flu that affects dairy cows is a strain of H5N1.

Only two of these vaccine candidate viruses are compatible with the strain of bird flu currently circulating.

Studies suggest that vaccines based on these two candidate viruses “will offer good cross-protection against outbreak viruses in livestock,” Demetre Daskalakis, director of the National Center for Immunization and Respiratory Diseases, said in a May 1 phone call. .

However, Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security at the Bloomberg School of Public Health, cautioned that the vaccine candidate viruses are not a “perfect match” for the H5N1 strain that currently circulating. This means they may not produce very effective vaccines at preventing disease.

Additionally, research conducted in the mid-2000s found that H5N1 vaccines do not trigger a strong immune response in people unless they are given in a large enough dose; or if it is administered with a compound known as an adjuvant, which stimulates the immune response.

Adalja noted that the H5N1 vaccines we have in stock really aren’t that good at provoking an immune response.

“Even for the viruses they target,” says Adalja. “In clinical trials, the levels of protective antibodies that people had were modest.”

One of these existing H5N1 vaccines in the NPIVS is manufactured by CSL Seqirus, which supplies flu vaccine to the US market.

Still, Diemert believes that a bird flu vaccine based on the two candidate vaccine viruses in the NPIVS would be effective and potentially more effective than seasonal flu vaccines.

This is because a bird flu vaccine would probably only need to target a single strain of virus.

In contrast, during the seasonal flu season, multiple strains of flu may spread. Seasonal flu vaccines are developed to target certain strains of flu each year. Vaccines are developed in the summer and early fall by analyzing strains common in the southern hemisphere. But during flu season, the strains that become more common in North America may not be the strains the vaccine was intended for.

As a result, seasonal flu vaccines may end up targeting strains of the flu virus that are not those in circulation that year.

“That’s one of the reasons why (seasonal flu vaccines) are not 100% effective because they are not a perfect match,” Diemert said.

Before bird flu vaccines can be rolled out, they would have to be approved by the Food and Drug Administration (FDA), but the agency has a process for approving seasonal flu vaccines updated each year.

Therefore, this should go smoothly, Diemert said, “especially since the (bird flu) vaccines would be made using the same manufacturing process they use every year (for seasonal flu vaccines).”

Additionally, “I’m sure that if there was a massive outbreak of this particular strain, then the FDA would expedite things,” he said. “So I don’t see regulatory approval being a rate-limiting step.”

In terms of getting the vaccine to the people who need it most, “all the elements are in place to be able to roll out a vaccine relatively quickly,” Diemert said.

However, “when (the vaccine candidate virus) is sent to the manufacturer, it still takes weeks or months to produce all the doses that are needed,” he said.

This is especially difficult in a “rapidly changing situation” like a pandemic, said Peter Chin-Hong, MD, an infectious diseases physician at UCSF Health.

Federal health officials estimate more than 100 million doses could be shipped within three to four months. However, they expect people to need two doses, so this would only cover 50 million people.

Vaccine production could also be affected by the same virus that the vaccine would protect against.

Manufacturers typically use chicken eggs to produce flu vaccines, but chickens are also susceptible to the bird flu virus that affects livestock.

So, “if there is a global (influenza) pandemic and birds also die, that can limit supplies like chicken eggs,” Adalja said.

As of May 6, more than 5 million chickens and other commercial or backyard poultry in the United States have been affected by highly pathogenic avian influenza (HPAI). which includes H5N1, reports the US Department of Agriculture.

The big question is whether enough vaccine doses could be distributed in time to make a difference.

“With the 2009 H1N1 pandemic, when the vaccine came out, the pandemic had already dissipated,” Chin-Hong said.

During that outbreak, tens of millions of Americans were vaccinated, but by the time vaccine doses became available, the fall wave had subsided.

However, “it’s 2024 and things have changed,” Chin-Hong said, referring to the rapid development and distribution of COVID-19 vaccines. “When people put their mind to it, it can be done quickly… But the devil is in the details.”

Overall, “it will take some time to prepare to be able to vaccinate everyone who is at risk of getting the flu,” Adalja said. “And as I said, the vaccine candidate virus that is in storage is not a perfect match. And even if it were a perfect match, (the H5N1 vaccine) is not a great vaccine to begin with.”

Federal health officials said the government is also pursuing an mRNA vaccine against bird flu, based on the same technology as Pfizer and Moderna’s COVID-19 vaccines.

Chin-Hong said this type of vaccine could be updated more quickly to match the strains of the virus currently circulating. But these vaccines have their own challenges, she said, such as the need to store them at extremely cold temperatures.

Additionally, since these vaccines would be a new use of mRNA vaccine technology, the FDA may require clinical trials that could delay their rollout to the general population.

There are other options for dealing with an outbreak of bird flu in people, including antivirals such as Tamiflu, which would be given to people who are already infected.

“Different interventions target different people,” Chin-Hong said. “In general, Americans prefer to treat something rather than prevent it, which can be a challenge.”

As seen during the COVID-19 pandemic, what matters is not just how many vaccine doses can be shipped, but also how many people receive the vaccines.

“The problem we may have is that there is more vaccine hesitancy now, so people may not be as willing to get vaccinated,” Diemert said. “I don’t know if that will be different because (chicken egg) flu vaccine technology has been around for decades and there is a lot of evidence of its safety.”

Chin-Hong pointed to current low COVID-19 vaccination rates among American adults as a sign of vaccine fatigue.

About 22% of all American adults have received the updated COVID-19 vaccine, with a slightly better rate (38%) among older adults. According to the Centers for Disease Control and Prevention. Both rates are much lower than health officials would like to see.

“It shows how fatigued people are (with vaccination campaigns),” Chin-Hong said. “This (hesitation) should be addressed at the same time as having a well-oiled plan (to roll out vaccines).”

Adalja is concerned not only about vaccine hesitancy, but also about growing public opposition to vaccines in general.

“In 2009, with the H1N1 flu, vaccination uptake was poor because the concerns raised by the anti-vaccine community (which were unjustified concerns) deterred people from getting vaccinated,” he said.

But “after COVID-19, the anti-vaccine movement is more powerful than it has been in decades,” he added. “That’s why I think mounting a vaccination campaign in a (future) emergency is going to be very difficult in the current political environment.”

There are no signs that the H5N1 bird flu circulating in dairy cow herds is developing the ability to spread easily to people. But federal health officials are planning to roll out a bird flu vaccine as a precaution.

The federal government has two candidate vaccine viruses in stock. These are weakened, so they can’t infect people or cause illness, but they grow well in chicken eggs, which is how the flu vaccine is most often made.

The vaccine candidate viruses are not a “perfect match” for the bird flu virus currently circulating, but they should offer good protection, health officials say. However, experts worry that vaccine fatigue will deter acceptance.