The Future of Flu Vaccines

One hundred years since the devastating Spanish flu pandemic that killed more than 50 million people, influenza viruses are still causing world-wide morbidity and mortality. According to the World Health Organization (WHO), seasonal flu causes 3 to 5 million cases of severe illness and 290,000 to 650,000 deaths per year worldwide. Vaccination is the first line of defence that slows the spread of seasonal influenza and prevents severe, life-threatening infections. The risk of fatal influenza infection is far higher in unvaccinated individuals, especially the elderly.

Flu vaccines deliver weakened or inactivated influenza virus into the body. Once immune cells detect and process virus parts they initiate the process of making antibodies. Antibodies neutralize invading viruses like influenza to prevent infection. When vaccinated people are re-exposed to influenza viruses, their bodies are prepared to produce large amounts of these antibodies and efficiently fight off infection.

Why do we need to get vaccinated against influenza viruses every year? Influenza viruses rapidly evolve in nature, especially on their surfaces. This means that the virus can disguise its identity to trick the immune system. Thus, we need to get new influenza vaccines each year to teach our immune systems to recognize the most recent viral ‘disguise’. 

In recent years, researchers have begun developing “universal influenza vaccines” designed to provide broader protection against many influenza virus strains with different surfaces. The main difficulty in developing a universal vaccine is an incomplete understanding of the human immune response to influenza infection. This summary describes two leading strategies for universal influenza vaccine development. The first strategy is to use a substance called an adjuvant in vaccine formulations to enhance immune protection. The word adjuvant is derived from the Latin and means “to help”. Besides boosting the immune response, adjuvants can also induce a long-lasting protection. The second strategy is to develop vaccines that stimulate antibody responses to a part of the virus that rarely changes over the years. The influenza virus is covered by proteins called ‘hemagglutinin’. Each hemagglutinin has a “head” and a “stalk” part (see image). The head part changes every year, while the stalk part remains the same. Recently, researchers proved that an influenza vaccine based on the stalk region of hemagglutinin could protect animals from infection. Moreover, vaccinated humans also produce antibodies against the conserved stalk region of hemagglutinin, which suggests that our own bodies are already equipped to process the stalk and use it to make antibodies. We just need to improve the efficiency of this natural process through vaccination.

We are still in the early stages of universal influenza vaccine discovery and development, but early findings are promising. After a century since the 1918 flu pandemic, we can finally see major progress towards the control of influenza worldwide.

Summary written by: Alyne Teixeira

To learn more about flu vaccine and associated research, please look at the following links:

Catharine Paules, and Anthony Fauci, “A Universal Flu Vaccine is Vital”

Florian Krammer, and Peter Palese, “Advances in the development of influenza virus vaccines”

Raffael Nachbagauer et al., “Induction of Broadly Reactive Anti-Hemagglutinin Stalk Antibodies by an H5N1 Vaccine in Humans”

Raffael Nachbagauer et al., “Hemagglutinin Stalk Immunity Reduces Influenza Virus Replication and Transmission in Ferrets”

Ashley P. Taylor, “First Universal Flu Vaccine to Enter Phase 3 Trial”