15 June 2017
A paper published today in PLOS Pathogens reports on a new study that has identified several genetic mutations in the avian influenza strain H7N9 that, should they arise, could potentially allow this type of flu virus to spread between humans. In response to this study, the BSI has issued the following statement:
Dr Fiona Culley, Spokesperson for the British Society for Immunology, & Senior Lecturer in Respiratory Immunology, Imperial College London, said:
“This is a good, thorough study which specifically aimed to identify which changes in bird flu would allow the virus to attach to human cells. One reason that bird flu is generally poor at infecting people is that it cannot attach to cells in human lungs. Rarely, strains of flu which are adapted to infect animals undergo changes or mutations that allow them to jump to infecting humans. This study aimed to understand what changes a bird flu virus would need to undergo to allow it to infect and transmit between people.
“Scientists have previously studied the differences in flu viruses before and after they made the jump from infecting animals to humans. This study attempted to generate mutations in the laboratory to predict which changes might allow a flu virus to jump species. The authors found that certain combinations of three mutations were needed for the bird flu to be able to attach to human lung cells. Some of the individual mutations have been seen naturally, but these combinations of mutations have not. They could potentially happen, but there is currently no evidence that they have ever occurred and the chances of all three occurring together is relatively low.
“One thing to note is that the authors only tested whether mutations in part of the outside of the flu virus altered the ability of that part of the virus to attach to human cells. One limitation of this study is that an ability to attach to human cells does not necessarily mean that a mutated bird flu virus will be able to infect and transmit between humans. They did not incorporate these changes into a whole virus and so were not able to directly test the ability of a virus with these mutations to infect and transmit.
“Changes which allow a virus to attach to human cells on their own might not be sufficient to allow the virus to replicate and transmit in humans. Other additional changes to the virus would probably be needed to allow it to be fully compatible with the machinery of human cells. The virus must also be stable enough to survive in the environment to be transmitted between people. In fact this study suggests that acquisition of the mutations that allow the virus to attach to human cells may come at the price of reduced stability.
“Scientists want to find ways of identifying which strains of bird flu have the potential to become adapted to surviving and transmitting in the human population, so that we can better monitor and prevent infections spreading.
“Flu viruses are known to be able to mutate their outer surface fairly readily. This is a strategy used by circulating viruses which already infect humans to slowly change their appearance to avoid existing immunity within a population (in a process known as genetic drift). This continuous slow change in circulating flu viruses is why we have to produce a new flu vaccine each year to match the modified flu viruses that arise each year. Combinations of mutations that would allow a flu virus to jump from infecting one species to another are very rare.
“There is no threat posed to the UK identified in this study. These combinations of mutations have not been found naturally. The authors did not incorporate any of the mutations into whole virus particles so there is no risk of having made a new potentially dangerous virus in the lab.
“This study will help us to monitor the risk posed by bird flu in a more informed way and increasing our knowledge of which changes in bird flu viruses could be potentially dangerous will be very useful in surveillance. Scientists are continuously on the lookout for new strains of flu which pose a danger to human health. If a new flu virus jumps from animals to humans, this is a major concern. These new viruses could spread quickly in the human population as there would be very little pre-existing immunity. Furthermore we would not be ready with a vaccine for this new flu strain and it could take a long time to manufacture sufficient quantities of vaccine. In the long term, scientists would like to develop a universal flu vaccine that would protect against all strains of flu, even when new strains make the jump from birds to humans.”
The full study that this comment is in response to can be found at: de Vries et al. 2017 PLOS Pathogens doi:10.1371/journal.ppat.1006390