Flu season is in full swing in Australia and 2017 has the potential to be the biggest on record, according to the Immunisation Coalition, with more than 70,000 cases of flu reported to mid-August.
‘This is not just the biggest on record but the largest flu outbreak we’ve seen for some time,’ comments Paul VanBuynder the Chairman of the Immunisation Coalition. The previous record was in 2015 when more than 100,000 people tested positive for the flu.
Flu reaches an epidemic peak during July and August in non-tropical countries. This year, the number of laboratory-confirmed flu virus infections began rising earlier than usual and hit historic highs in some Australian states.
Flu viruses are broadly grouped into Influenza-A and Influenza-B. Influenza-A viruses are usually H3N2 - the main player so far this season, explains Ian Mackay, a virologist at The University of Queensland. Influenza-A viruses are more variable; multiple flu viruses circulate each year.
While the reasons for the record-breaking transmission flu rates this season remains unclear, another factor could be due to low flu vaccination rates. Each season new flu vaccines are designed based on detailed characterisation of the flu viruses circulating the previous season. But the viruses that end up dominating the next season may change in the meantime.
‘As far as we know the vaccine is well matched,’ says Mackay, ‘but we won’t know for certain until more flu strains have been characterised. H3N2 viruses can change even within a season and this may be one reason for such a big season.’
What does this mean for the northern hemisphere’s winter? ‘The northern hemisphere vaccine is well matched for what is expected to predominate,’ Mackay says. ‘In fact, it is recommended to contain the same viruses as the southern hemisphere’s vaccine has. If the virus has changed during our season, though, then with winter in the north may come a larger than usual flu epidemic.’