By Meghna Badami
The world witnessed a global influenza pandemic a decade ago in 2009. More recently, the United States witnessed a massive outbreak of H5N2 in 2015. Each year, a novel strain of virus is transmitted through animals that can potentially cause an outbreak. The fast rate of mutation means that we have to fight a different strain, with a different vaccine each flu season! Hence, a Universal vaccine is every Public Health worker’s greatest dream.
Influenza viruses are of four types; A, B, C and D. Out of the four, A and B are known to cause flu outbreaks each winter. These viruses belong to the family of RNA Viruses- Orthomyxoviridae. Viruses belonging to the Influenza A genera are most virulent in humans and cause the most severe disease.
Breaking down the structure of the virus: Each Influenza virus has a protein coat which bears proteins that are present across every strain; Within the protein coat lies the genetic material which varies with each strain.
The Influenza A virus consists of two major proteins Hemagglutinin (H) and Neuraminidase (N). There exist 18 different types of Hemagglutinin and 11 different Neuraminidase protein, and the type of H and N protein present determines the subtype of Influenza A virus. For example, the strain H1N1 has type 1 Hemagglutinin and type 1 Neuraminidase proteins. The Hemagglutinin protein consists of a head and a stalk.
Traditional Influenza vaccines are created for a flu season after calculated predictions about which strain will affect populations that particular year. Annual flu shots protect 60% of the population. These vaccines target the genetic material which is specific to each strain. It protects against a few strains of A and B, but doesn’t protect against C strains and other mutated versions. This means that even after getting a flu shot each year, you aren’t guaranteed of immunity! Furthermore, the process of predicting strains and synthesizing new vaccines proves to be too cumbersome. With over a hundred centres in various countries conducting a year round surveillance and a Biannual seasonal viral strain selection process, it takes 6 months to produce a vaccine. Therefore, a Universal vaccine - one shot that provides immunity to all strains of influenza in one go - is not only advantageous, but necessary!
As mentioned earlier, the H and N protein subtypes are present across all strains and hence targeting them would immunize people against a majority of strains. The Hemagglutinin stalk domain is, in fact, so similar between strains that epitopes on this molecule are now being targeted.
Another advancement in the field is University of California, Los Angeles's "Goldilocks" vaccine that manages to trigger a strong immune response without affecting the health of the affected animal. Furthermore, newer viral vaccines use live viruses as opposed to the older ones which used killed viruses that didn't cause a significant T cell reaction.
A team from NIAID painstakingly engineered the stalk of Hemagglutinin and proved that nanoparticles of H1 could provide immunity against strains with H5. This design is undergoing clinical trials at the moment.
There are several avenues being explored and some yet to be explored with the flu vaccine and a universal vaccine doesn't look too distant a dream anymore!
A huge thank you to Dr Shashank Tripathi and the entire team at ST labs, Centre for Infectious Disease Research, Indian Institute of Science for their guidance and inputs on this article.