The first ever avian influenza vaccine recently started trials in the UK. This marks a milestone in the prevention of bird flu infections in humans.
The vaccine targets the H5N1 flu strain, which causes severe infections in bird populations worldwide. However, this strain of bird flu virus is also able to spread to humans in rare cases through direct contact with infected birds or poultry products.
This latest trial hopes to test the vaccine in people who are most at risk of acquiring bird flu. This includes people who work in poultry industry and people who are above 65 years of age.
Bird flu vaccine
This new bird flu vaccine is an mRNA-based vaccine. This is the same technology that was used in some COVID vaccines.
Messenger ribonucleic acid (mRNA) acts as a messenger between the genes and the microscopic factories inside human cells that produce proteins. It carries a message from the genes to these cellular factories to produce proteins with specific structures.
For instance, mRNA plays a role in producing the enzymes that regulate our metabolism, the haemoglobin that carries oxygen to our tissues and the antibodies that protect us against infections.
Vaccines that use mRNA technology deliver instructions to cellular protein production factories, telling them to produce certain proteins that are normally present on the surface of a specific virus.
By doing so, these vaccines generate a fake disease which is less severe than the actual disease caused by the virus. The immune system sees the viruses or any parts of them (such as proteins) as intruders and tries to destroy them.
Once the fake disease has been suppressed, the immune system will hold a memory of this particular virus. That way, if a person contracts the virus in the future, the immune system will respond very quickly and very strongly to destroy the viruses and stop the spread of the disease.
But in order for an mRNA vaccine to be effective, it needs to be efficiently transported from the site of administration to the blood and immune cells. Like a letter that needs an envelope to be delivered from sender to recipient, the mRNA also needs the right carrier so it can be delivered to the immune cells.
Similar to the COVID vaccines, this new bird flu vaccine uses microscopic fatty spheres called lipid nanoparticles to carry the mRNA. These microscopic envelopes are around 100-200 manometers in size (that’s almost 100,000 times smaller than a penny).
They’re made of a combination of different fats (lipids) that form a microscopic sphere inside which the mRNA is enveloped. Different combinations of fats are used to customise the lipid nanoparticles to the cargo they carry. This maximises the mRNA load they can carry and ensures they don’t fall apart before delivering their cargo.
Before the introduction of mRNA-based vaccines and lipid nanoparticle technology, most influenza vaccines were developed by genetically modifying or chemically inactivating the viruses. While these live attenuated or inactivated viruses couldn’t induce a full scale infection, they still triggered an immune response.
But this process was very costly, time consuming and had varied success. So it was only reserved for the viruses that were on the World Health Organization’s priority list. As bird flu has historically posed a low infection risk to humans, there hasn’t been an incentive to develop a vaccine for it.
nobeastsofierce/ Shutterstock
But advances in mRNA technology and lipid nanoparticles have now provided us with the tools for developing effective vaccines against a greater number of viral infections in a fast and cost-effective manner – including lower priority diseases, such as bird flu.
Preventing the next pandemic
Although bird flu currently poses a very low threat to humans, it does have the potential to cause a pandemic if its spread is not controlled.
There are some key reasons for this. In birds, H5N1 is highly virulent and new strains evolve rapidly. It also has the potential to crossover into a variety of mammalian species – including humans.
Infection with bird flu can cause severe illness that is hard to treat in vulnerable people. This includes those over the age of 65 and people with a compromised immunity (such as cancer patients and people who have received organ transplants). Therefore, it could have serious repercussions if the virus was able to spread more readily between birds and humans.
The vaccine trial is a proactive attempt to protect people against the possibility of a future pandemic and to protect those who are more vulnerable to severe bird flu infections.
The lipid nanoparticle technology the bird flu vaccine uses also has broader health applications beyond infectious diseases. One application is in developing cancer vaccines, where they will be used for treating an existing cancer in patients.
I lead a research group at the University of Portsmouth that works on developing new mRNA-based vaccines against different types of cancer including breast, cervical and colorectal cancers using lipid nanoparticles. The same technology is used in Moderna’s mRNA vaccine against melanoma that is currently in trial in the UK.
The mRNA that is used in cancer vaccines instructs a type of immune cell called dendritic cells to produce the same proteins that are expressed on tumour cells. The lipid nanoparticles act as envelopes to carry this mRNA to these cells.
These cells produce and present the cancer proteins to the other members of immune system, including T cells. As a result, the body will see the tumour cells as an intruder and will try to destroy them just as it does with the viruses.
Advances in mRNA synthesis and lipid nanoparticle technology mark a new era in vaccination. These new technologies enable us to produce new vaccines more quickly and to customise them to achieve higher effectiveness. This is of paramount importance for preventing pandemics in the future.
