US clinicians are concerned for their upcoming influenza season, following record outbreak numbers in Australia
Reports from Australia have caused “mounting concern” for health professionals in the US, who are looking to the Southern Hemisphere to predict what may be in store for them.
Australia’s 2017 influenza season saw record-high numbers of laboratory-confirmed flu notifications, and higher-than-average numbers of hospitalisations and deaths.
The number of notifications reached 215,280 by mid-October, which far exceeded the 59,022 cases reported during the 2009 H1N1 influenza pandemic.
While the implications of this for the Northern Hemisphere are not clear, infectious disease and public health experts note the vaccine for the US upcoming season has the same composition as that used in the Southern Hemisphere.
“We much consider whether our current vaccines can be improved and whether longer-term, transformative vaccine approaches are needed,” they write in the New England Journal of Medicine.
They say reasons that vaccine effectiveness may be suboptimal include:
- Vaccine mismatches
- Prior influenza exposure and vaccination history
- Age and coexisting conditions
- Production/manufacturing methods
In particular, as has been suggested before, egg-based production can lead to amino acid changes that modify proteins which mediate receptor binding.
Interim reports suggest that the lowered vaccine effectiveness during this year’s Australian influenza season was not attributable to antigenic mismatch.
Rather, evidence shows that egg-propagated vaccine viruses acquired changes that subsequently altered antigenicity against circulating strains.
The authors say that in years when flu vaccines are well matched there is an effectiveness range from 40-60%.
However in Australia this year, the flu vaccine’s effectiveness was much lower against influenza A (H3N2) viruses.
“This observation lends credibility to the hypothesis that egg-adapted changes contribute to poor influenza-vaccine effectiveness,” they say.
And given that most of the US influenza-vaccine supply is currently produced in eggs, they say it is possible the US will also experience low vaccine effectiveness against influenza A (H3N2) viruses and also have to endure a “relatively severe” season if these viruses predominate.
According to a study from scientists at The Scripps Research Institute (TSRI), published one month ago, the common practice of growing influenza vaccine components in chicken eggs indeed renders the flu vaccine less effective in humans.
“Now we can explain — at an atomic level—why egg-based vaccine production is causing problems,” said TSRI Research Associate Dr Nicholas Wu, first author of the study that was published in the journal PLOS Pathogens.
The study showed egg-based manufacturing of vaccines led to the mutation of a key protein, disrupting the region on the protein that is commonly recognised by our immune system.
This means a vaccine containing the mutated version of the protein will not be able to trigger an effective immune response, leaving the body without protection against circulating strains of H3N2.
Mr Wu’s analysis revealed the current strain of H3N2 used in vaccines already contains this specific mutation.
“Vaccine producers need to look at this mutation,” he cautioned.
The researchers say further studies are needed to investigate replacing the egg-based system.
“Other methods are now being used and explored for production of vaccines in mammalian cells using cell-based methods and recombinant HA protein vaccines,” explained study senior author Ian Wilson, Hansen Professor of Structural Biology at TSRI.