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Scientists Are Developing mRNA Bird Flu Vaccine

An experimental bird flu vaccine was found to be highly effective in preventing severe illness and death in animals, raising hopes that it could help manage the outbreak circulating in birds and dairy cows in the United States.

The second U.S. human case of avian influenza virus H5N1, most likely contracted from dairy cows, prompted fears about a possible outbreak as the world is still grappling with the consequences of COVID-19.

Both patients had only mild disease with conjunctivitis and fatigue as symptoms, leading to experts' warnings that the mildness of the infection may allow it to go undetected and spread between people.

Epidemiologists agree that there is no need to panic about human infections at this time, and the United States is much better prepared for the spread of bird flu than it was for SARS-CoV-2 in 2020.

Meanwhile, scientists at the Perelman School of Medicine at the University of Pennsylvania are developing a vaccine against bird flu, which has shown high effectiveness in preclinical models.

The preclinical trial of an experimental mRNA vaccine was published in Nature Communications.

The experimental vaccine targets a specific subtype of the H5N1 virus that is circulating widely in birds and cattle. The vaccine elicited a strong antibody and T-cell response in mice and ferrets. The animals maintained high levels of antibodies even a year after receiving the vaccine.

When vaccinated animals were infected with H5N1, they cleared the virus more rapidly and displayed fewer symptoms than unvaccinated controls.

In the study, all vaccinated animals survived H5N1 infection, whereas all the unvaccinated died.

Compared to a traditional egg-based influenza vaccine, the experimental mRNA vaccine in mice was as effective. Both vaccines elicited strong antibody responses, regardless of prior seasonal flu exposures.

"The mRNA technology allows us to be much more agile in developing vaccines; we can start creating a mRNA vaccine within hours of sequencing a new viral strain with pandemic potential," said Scott Hensley, Ph.D., a professor of microbiology at the Perelman School of Medicine.

A new technology is needed

An egg-based influenza vaccine manufacturing process has been used for more than 70 years and involves growing candidate vaccine viruses (CVVs) in chicken eggs.

These CVVs are injected into fertilized chicken eggs and incubated to allow the viruses to replicate. The fluid containing the virus is then harvested from the eggs.

The study authors say it can take up to six months for these vaccines to be produced, while vaccines are needed most during the first few months of a pandemic.

Meanwhile, some experts worry that wild birds could carry the virus into the hen houses necessary for vaccine manufacturing, making the technology unreliable during the outbreak.

Over 92 million birds have been killed since the avian outbreak began in 2022, according to the U.S. Department of Agriculture.

Bird flu infections in humans remain rare. From January 2003 to February 2024, 887 cases were reported from 23 countries, with a mortality rate of 56%, according to the World Health Organization.

People usually get the virus after close or lengthy unprotected contact with infected birds or places sick birds' saliva, mucus, and feces have touched.

Drew Weissman, M.D., Ph.D., a co-author of the study, said in a statement, “COVID-19 showed us the power of mRNA-based vaccines as a tool to protect humans from emerging viruses quickly, and we are better prepared now to respond to a variety of viruses with pandemic potential, including influenza.”


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