The unexpected resurgence of a strain of influenza no longer included in the subsidised vaccine is partly to blame for Queensland's horror season.
Queensland's horror flu season should pass soon despite a strain that was previously vaccinated against making an unexpected comeback, health authorities say.
More than 18,000 cases of influenza have been reported in the state so far this year, with roughly 3000 reported last week alone.
This is partly due to the resurgence of the so-called B Brisbane flu, which wasn't included in this year's three-strain subsidised vaccine.
Instead, the government-funded dose provided protection against Influenza A California, Influenza A Switzerland and Influenza B Phuket.
While the nominated strains are set in February in anticipation of each year's flu season, people can pay more for a four-strain vaccine for extra protection.
Executive Director of Queensland Health's Communicable Diseases Unit Dr Sonya Bennett said the surprising prevalence of the Brisbane strain was partly to blame for this year's spike in overall cases.
"The proportion of B Brisbane does seem to be rising," she said on Tuesday.
She said the secondary B strain typically only accounted for about five per cent of cases and was less severe than an A-strain virus.
The Brisbane strain had been in the subsidised vaccine mix between 2010 and 2012.
Despite its shock revival, Dr Bennett said the department expected the worst to be over soon.
"It is difficult to predict when the flu season will be over but figures suggest we are nearing or have reached the peak," she said.
But some experts are calling for the federal government to consider coughing up for a four-strain flu vaccine to ensure future flu seasons aren't so severe.
Influenza Specialist Group chairman Dr Alan Hampson anticipated this could happen in coming years after the government begins a new tender process with manufacturers.
He conceded it was rare for B-strain infections to outweigh their A-strain counterparts, but said this year's experience just reinforced the need for a four-strain vaccine.
"Influenza is really unpredictable," Dr Hampson said.
"You just don't know until the last moment, until the virus is out there and circulating."