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Cardiologist Professor Harvey White fears New Zealanders are too blasé about the risk of Omicron infection, which has been painted as mild for most people.
In a letter to the editor in today's Herald, White - who is director of cardiovascular research at Auckland DHB - says even "mild" initial infections can lead to serious long Covid symptoms, including higher risk of heart attack and stroke.
He fears the long-term complications of Covid will put major stress on our health system, and is urging people to get boosted and try to avoid catching the virus.
Long Covid covers a range of symptoms, from brain fog and impaired thinking to memory loss, anxiety and fatigue, heart disease and stroke.
"Between 10 to 30 per cent of people infected with Covid-19 may develop long Covid," White writes, adding that a tidal wave of heart disease is also on its way.
"Omicron can acutely attack the heart but long-term after recovery, blood pressure may go up, heart rhythms may become abnormal, and decreased pumping function of the heart with heart failure and shortness of breath may occur."
White hasn't yet seen a surge in Covid-related heart disease at work, but he expects it's imminent. A recent study in the US of 153,000 veterans found heart disease risk increased substantially in the year following an infection, even in mild cases.
That could be due to secondary reasons like stress and people putting off medical care, but could also be directly due to Covid, White said. Those who had had Covid had a 63 per cent increased risk of heart attacks and 52 per cent increased stroke risk.
World Health Organisation Covid expert Dr Maria Van Kerkhove said earlier this month she had seen no evidence that Omicron caused less long Covid than previous variants.
Long Covid is defined as symptoms arising three months after the initial infection, White told the Herald.
"Omicron was only discovered in November so we've barely had three months to collect data - but everything suggests it's likely to be the same [as previous variants]."
There were 14,940 cases of Covid confirmed on Sunday alone, bringing New Zealand's total to 85,667 since the pandemic began, according to the Ministry of Health.
Extrapolating from the veteran study, White said if one million New Zealanders caught Omicron, he would expect 300-900 additional heart attacks and 400-1200 extra strokes in the year after they were infected.
That was based on the estimates of 10-30 per cent of Covid cases developing long Covid. And some of those heart attacks and strokes would happen in people whose infection was "mild", meaning they did not go to hospital for their initial infection.
Covid could cause organ damage throughout the body, including to the heart and blood vessels. It could also make the immune system go haywire and attack itself, creating "autoantibodies", and could reactivate underlying viral illnesses that were caught earlier in life, White said.
Even the fact that there were now more than 300 people in hospital with Omicron showed catching the virus was "not trivial".
People could help decrease the tidal wave by trying to avoid infection and getting vaccinated and boosted, which provided good protection against long Covid.
But White was concerned about a large group of eligible people who had not taken up the booster vaccinations, as well as those who remained unjabbed.
"People aren't getting revaccinated, boosted to the highest rate. They're not taking care, in my view, with mass gatherings and wearing masks and so forth.
"To see this explosion of Covid cases and to keep telling people that it's mild, I think that's wrong. Individually, we have to really avoid it."
He also said anyone who developed heart symptoms after catching Omicron should see their GP immediately.
In a statement, a Ministry of Health spokeswoman said the long-term physiological and psychological effects of Covid-19 were not yet known.
"However, new evidence around long Covid-19 continues to evolve around the globe and the ministry is continuing to watch developments very closely. Part of that evidence includes the long-term health impacts of long Covid-19."
The ministry had published guidelines around the rehabilitation for people after an acute Covid infection which would be updated to include long Covid.
It had also completed a comprehensive literature review and planned to establish an expert advisory group to advise on what long Covid meant for New Zealand.
And the ministry had funded an Impacts of Covid-19 in Aotearoa study at Victoria University of Wellington to understand the "lived experiences" of people impacted by Covid-19, including long Covid.
"The outcomes of the study will be used to advise health officials."
Meanwhile, Dr David Welch from the Centre of Computational Evolution said the idea that Omicron infection was inevitable "so we should just get on with it" was incorrect and could be dangerous for the healthcare system and the economy.
"The majority can avoid being infected during this Omicron wave and we should all do as much as we reasonably can to avoid infection.
"Actions we take do help us to stop getting sick and protect our health system and economy."
Welch said in hard-hit places, around 50 per cent of people avoided infection and 80 per cent in places where the virus was controlled better.
"The actions we take over the next three to five weeks will determine whether the outbreak is manageable or not."