The Science Behind Vaccines

Why is the influenza virus moving from birds to pigs, cows and sometimes humans?

In the spring of 2024, reports about increased cases of a particular variety of avian influenza (aka ‘bird flu’) called H5N1 has been in the news and has caused public concern. H5N1 is a type of bird flu that has been shown to spread from birds to mammals and occasionally infect humans who come into close contact with infected birds and their droppings. What has made this more concerning in 2024 is that H5N1 was found in cows and infected a few humans who had close contact with the infected cows. This strain of the flu virus is concerning as it can cause severe illness in both birds and humans.

Vaccines can be used not only to protect humans, but also to protect livestock such as chickens, pigs and cows to limit a virus’s ability to jump between species and therefore limit how far it can spread.

Your immune system is incredible at remembering the shapes, sizes and styles of different viral or bacterial invaders and training cells to find and kill those pathogens, especially if they invade your body a second time. This is why we create vaccines – we use our knowledge of the ability of the immune system to train and remember pathogens to protect our communities and strengthen public health.

How do flu vaccines work?

Influenza vaccines contain dead viruses that are used to train your immune cells to remember the pathogen. Think of your immune cells as martial artists who train by fighting with a weakened version of the enemy to learn how to successfully defeat the enemy when they are in a real battle. This training gives your immune cells clues about what to look out for and how to fight to win the battle, or in this case, infection with the influenza virus.

A specific type of immune cell, called the B cell, will use its training to create memory cells as well as to produce specialized proteins called antibodies. The memory B cells will recognize the virus when it enters again in the future and immediately take action to defend the body while the antibodies will surround the enemy and tag it for destruction by other immune cells.

How is your team working to design the best vaccines to protect us from influenza?

The research team is looking at how to design vaccines that encourage antibodies to recognize the most common elements of the flu virus. This is because every year the virus changes small things about its appearance (e.g. changing your hair color, getting a new haircut or wearing different styles of clothes) to try and slip past the immune system, making it tricky to find again.

If instead of focusing on the superficial outer appearance of the virus, we could generate antibodies that were trained to recognize things that are more difficult to change or hide (e.g. your height, face shape or foot size), those antibodies could be successful in helping your immune system defend the body from year-to-year even as the virus makes small changes to its outer appearance.

Antibodies that would be successful in this way are called broadly neutralizing antibodies. In the best-case scenario, these broadly neutralizing antibodies could provide universal protection against many or all types of influenza virus infection.

Guest contributor: Jenna Guthmiller, PhD, is an assistant professor in the Department of Immunology and Microbiology at the University of Colorado School of Medicine.