A new weekly flu report released yesterday shows the trend of reported influenza strains is continuing to rise steeply.
Data obtained by the Herald from the latest Environmental Science and Research influenza report, dated July 6-12, shows there have been 247 reports of both A and B strains of the virus - 55 more than the week before.
Of these reported cases, there were 162 reports of the A strain in the North Island, compared with seven in the South Island.
However, the South Island - which has a smaller population - has had 52 reports of the B strain, compared with just 26 in the North Island.
Dr Lance Jennings, Canterbury District Health Board virologist and spokesman for the National Influenza Specialist Group, said this week's report shows the curve was steeply rising, tracking very similar to the 2011 curve.
"Influenza activity is increasing at the present time, it's what we characteristically see - these steep rises as the virus spreads throughout New Zealand and causes these explosive outbreaks of infection.
"And we've seen that with Bay of Plenty being affected, and then Hawkes Bay, and now Wellington region being affected."
He said this causes considerable burden on the health systems of those regions for a short period.
Dr Jennings said they did not know whether the levels were going to reach the 2010 or 2012 peaks, or whether it was going to follow what they have seen in recent years.
"I anticipate that [with] the school children going back to school next week we're going to see this curve go up for one or two weeks and then taper off."
Health Minister Jonathan Coleman announced on Wednesday that the influenza immunisation programme would be extended until the end of next month.
The extension followed reports of the unusual pattern of sickness developing in the North and South Islands, with health professionals recording peaks of different influenza strains - something not seen in more than 30 years.
"The A-H3N2 strain, which is covered by the vaccine, appears to be the predominant type - this strain affects the elderly and very young more severely than other strains," Dr Coleman said.
Dr Jennings said last night that New Zealand was about 10,000 flu vaccines short of last year's record of 1.20 million doses distributed.