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If the proteins change in a major way — what scientists call an ‘antigenic shift’ — it can cause a pandemic, which is what happened with swine flu in 2009 with the A (H1N1) strain. The situation in Australia is what’s described as an antigenic drift, rather than shift, which means the virus has mutated in a minor way; it’s still causing problems, because we have less immunity to it (immunity builds up from exposure to viruses from previous seasons), but nothing like the scale of a pandemic.The spike in Australian cases has been caused by influenza A (H3N2) subtype, a strain that’s been circulating in humans since 1968.The flu season extends over many months, from November to March, and peak vaccine immunity in the elderly is about five to six weeks after they have had their vaccine, he says.A booster dose would seem to make sense, says Professor Cheng: ‘We suggest waning immunity is taken into account when considering when people are vaccinated.’That is, whether they should get jabbed when the vaccine first becomes available, or whether they can wait for three or four months until June or July during the Australian winter, he says.He suddenly passed away two days later from flu complications.Ben was a tragic victim of one of the worst flu outbreaks on record in Australia, with the number of cases two-and-a-half times higher than last year.If 50 per cent effectiveness is regarded as good for the general population, for older people the figure is lower.In the UK last winter the vaccine did not work at all in those aged 65 and over, but the previous winter, effectiveness was 29 per cent.‘The effectiveness in older people could be down to 20 per cent because their immune system is not so strong and they do not respond so well to a vaccine,’ says Professor Booy.
The composition of this year’s vaccine, chosen by the World Health Organisation (WHO) in March, contains strains of A and B viruses, including H3N2.
It’s a virus to which the elderly are particularly susceptible (similar to one that circulated in the UK in the winter of 2014/15, causing a significant number of deaths).