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There have been just three laboratory confirmed flu cases this year in New Zealand, and all have been in MIQ. The lack of cases is part of a global trend, which is puzzling scientists.
University of Otago, Christchurch campus, virologist Dr Lance Jennings said the trend was unexpected, even in the face of international border closures due to Covid-19.
It was a mystery, as scientists did not fully understand why it was happening.
"We might have expected it if we had an influenza A pandemic, because we have seen it before, but with this virus (Covid-19) spreading globally, it’s unexpected,” Jennings said.
In the 2009 H1N1 flu pandemic, some other flu strains had disappeared.
While reduced air travel and border management controls were considered by many to be a cause, Jennings personally thought it was due to the phenomenon of a dominant virus, in this case Covid-19, filling an ecological niche and not leaving any room for flu viruses.
But Jennings did not rule out a late flu surge this winter.
There were four strains of influenza circulating globally, albeit at a low level.
These were two A subtypes and two B lineages, which were covered by this season’s flu vaccine.
“As we know with influenza, we always expect the unexpected," he said.
While New Zealand is considered most at risk of flu entering through the travel bubble with Australia, the Sydney Morning Herald recently reported there has been only 71 confirmed cases across the Tasman, compared to more than 30,000 in May in 2019.
Director at the World Health Organisation, National Influenza Centre, at Environmental Science and Research in Wellington, Dr Sue Huang, said the low number of cases this year, and at the end of last year, is “quite extraordinary.”
"I’ve never imagined that we would experience this kind of situation," Huang said.
She has worked in flu surveillance for about 20 years.
The median number of laboratory confirmed cases during flu season from April to September from 2015 to 2019 is about 5000. Last year there were 502 cases, with only two of these occurring from October to December.
Huang said it was still important to be vaccinated to protect vulnerable people.
She believed the drop in cases had been assisted by border closures and is “powerful” testimony to the value of public health measures, such as social distancing and hand washing.