People could be particularly vulnerable to the flu this winter, as several factors converge.
Official statistics show about 1000 lives have been saved in New Zealand during the last two winters when there has been very little influenza.
New Zealander Dr Richard Webby is a virologist at the St. Jude Children's Research Hospital in Memphis. Photo: Supplied
Listen
But Richard Webby from St Jude Children's Research Hospital in Tennessee expects people will be less resistant this time.
He said the US flu season coincided with the peak of Omicron, which dampened its spread, although it is possible to catch both the flu and Covid together, it is less likely.
"These are two viruses that target the same place in your body, so in the upper respiratory tract, in your nose and that environment - what tends to happen is that one wins out over the other."
Webby said when someone is infected by a virus there is a type of non-specific immunity they develop which makes them resistant to catching another virus that targets the same area.
"We do think that once you get one virus there is a period of time where you're less susceptible to other viruses that are trying to get into that same part of your body."
Webby said the timing of the Omicron peak with the flu season may less fortunate for New Zealand than it was in the United States.
The typical New Zealand flu season is around June to August and the Omicron peak could be around April, he said.
"So as you're coming into the New Zealand winter flu season there might be less Covid around and that really will open the door ... you know as travellers are coming back into the country they're going to bring flu with them and potentially seed it."
He said it is well documented that flu has not been circulating in New Zealand in recent times.
Webby said past studies have shown that 20 to 30 percent of New Zealanders get their immunity boosted by exposure to flu during a flu season.
"So now that you guys have been through two seasons without any of that boosting by natural infection, there is this concern that the overall immunity to flu is going to be lower."
Webby said that because there has not been much flu around, it is also trickier to formulate a flu vaccine.