Bird Flu Protection's New One-Two Punch: 'Priming' With One Vaccine, Then Boosting With Another

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A new study found that one bird flu vaccine can prepare people to better fight new strains, after receiving a second dose from a different vaccine. Photo courtesy of Shutterstock

Priming or preparing people with one vaccine, then boosting them with another, might be the best way to deliver protection against the avian flu, according to a new study.

Researchers have discovered that a vaccine protecting against an old avian flu strain can prepare the immune system to better respond when injected with another vaccine against a new avian flu strain. In addition, when the new vaccine was combined with an adjuvant — which stimulates the immune system to produce more antibodies — only a small dose of the new avian flu vaccine was required to have the same response.

“This is important because of the need to respond quickly to potential pandemics,” Dr. Robert Belshe, a professor of infectious diseases, allergy, and immunology at Saint Louis University who was lead author of the article, said in a press release. “We continue to see avian flu as the possible cause of a pandemic virus in the future. Planning for influenza pandemics is of vital importance, with vaccine being a cornerstone of control efforts.”

The study, published in JAMA, was led by researchers at Saint Louis University and analyzed two H5 influenza vaccines. It involved 637 healthy adults aged 18 to 49, many of whom had participated in a previous study and had received the Vietnam bird flu vaccine, which is one of the vaccines that the Centers for Disease Control and Prevention (CDC) has in stock in case of an outbreak. Those who received the first dose were considered “primed.” These participants then received a dose of the new vaccine known as the Anhui bird flu vaccine.

What the researchers found, interestingly, was that people who received this double punch of vaccination had developed an immune system memory of sorts that could better fight the new strain. “People who had been primed a year ago when they received the Vietnam bird flu vaccine had developed an immunologic memory,” Belshe said in the press release. “Our findings suggest if a threat of bird flu spreading from person to person was very real, it makes sense to prime with a bird flu vaccine that is related to but does not directly match the circulating strain.”

Avian influenza — named due to its origin and connection with birds — can be divided into several different types, subtypes, and strains, according to the CDC. The three types are A, B, and C; and only influenza type A is divided into subgroups — H5, H7, and H9. Type A can infect birds, people, pigs, horses, as well as other types of animals, though wild birds are natural hosts. Type B, meanwhile, typically only infects humans, but Type A is the worst and most fatal and can cause pandemics.

“Influenza viruses are dynamic and are continuously evolving,” the CDC writes. They can change in two ways: antigenic drift and antigenic shift. Antigenic drift involves small, gradual changings occurring through point mutations in the genes that produce the main surface proteins on the viruses — hemagglutinin and neuraminidase (which is where the H and N come from in H5N1, H7N7, and so forth). Antigenic drift creates new strains that cannot be battled by antibodies created from previous strains. “This is one of the main reasons why people can become infected with influenza viruses more than one time and why global surveillance is critical in order to monitor the evolution of human influenza virus stains for selection of which strains should be included in the annual production of influenza vaccine,” the CDC writes. Antigenic shift, meanwhile, refers to a major change that creates a new influenza A subtype that has not affected humans before.

The results of the study are promising, but there’s still work to be done to see just how effective the 1-2 vaccination punch is. “We do not know what amount of antibodies would be associated with protection from infection, disease, or death,” Belshe said in the press release. “Each of these end points might have different correlates of protection. The continued drift of H5 avian flu viruses that the strain of H5 used for the boosting vaccine will need to be updated to keep pace with newer H5 bird flu viruses that emerge. Furthermore, the emergence of H7 avian influenza viruses as human pathogens will require a different priming vaccine than the H5 Vietnam vaccine used in the present study.”

Regardless, people who are at a higher risk of contracting bird flu — like health care workers, laboratory scientists, or field epidemiologists — might want to go ahead and get primed, according to the research team. “Whether priming itself has value in protecting against death is not known, but it is possible that primed individuals would have better outcomes in the face of avian flu infections,” Belshe said in the press release.

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