Seasonal viruses which we see year after year were once pandemic strains, but humans have now been exposed to these viruses and have some background immunity to them. We have found that the last decade has seen an acceleration in the number of flu strains infecting humans. Around years ago the world experienced the Spanish flu pandemic, and it took another 39 years for a novel influenza virus to emerge. It took a decade after that for the next one.
Since , however, we have seen seven novel and variant strains emerge. This is a very large increase compared to the past.
The reasons for this increase are unknown, but there could be many. One reason could be better diagnostics and testing; another could be changes in poultry farming and animal management practices, since influenza is a virus that affects humans, birds and many animal species; as well as changes in climate, urbanisation and other ecological influences. But none of these factors have changed at the same rate as the emergence of new viruses has escalated. This warrants new research to unpack the relative contributions of all the different possible factors.
Another change is advances in genetic engineering tools, which make it possible to edit the genome of any living organism, including viruses. The possibility of a lab accident or deliberate release of engineered flu viruses is real. Experiments to engineer influenza viruses have been published since , and remain controversial for the possible risk, compared to the relative possible benefit.
With so many more novel influenza viruses emerging and circulating, the probability of genetic mutation and emergence of a new pandemic strain is higher today than any time in the past. This is both in terms of pharmaceutical drugs and vaccines, and non-pharmaceutical interventions like personal protective equipment, quarantine, border control and banning of mass gatherings in the event of an outbreak.
National pandemic plans outline interventions and the best sequence of different interventions, as well as prioritisation of these interventions. Unfortunately, manufacturers are not able to reissue flu vaccines when this happens because of the way flu vaccines are created and produced for human use.
Lee says. Thus far, the vaccine has been most effective in protecting against the influenza A H1N1 and influenza B viruses, so there is still room for improvement in preventing influenza A H3N2 viruses.
The effectiveness of the flu vaccine varies from year to year and also may depend upon the age and health of the person receiving the vaccine. Does the flu shot for one strain help minimize the effects from a flu infection caused by another strain? Regardless of which flu strains cause an epidemic, there are undeniable benefits to receiving the flu vaccine, especially for those with chronic illness, pregnant women, infants, and the elderly.
J Virol. Adaptation of avian influenza virus to a swine host. Virus Evol. Origin of the pandemic H1N1 influenza A virus as studied by codon usage patterns and phylogenetic analysis. World Health Organization. Updated April Global epidemiology of avian influenza A H5N1 virus infection in humans, a systematic review of individual case data.
Lancet Infect Dis. Centers for Disease Control and Preventions. Influenza flu : Key facts about flu vaccines. Updated April 28, Updated October 11, Asha K, Kumar B. Emerging influenza D virus threat: What we know so far!
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