This can impact on people's jobs, their ability to work at all, and enjoyment of life. Fatigue is far more crushing than occasional tiredness. Loss of taste and smell takes the pleasure out of dining or walking in the park.
University of Otago molecular biologist Emeritus Professor Warren Tate has said that many of those with "long Covid" have similar symptoms to chronic fatigue syndrome.
Closing the borders early on in the pandemic reduced the number of deaths and infections from Covid in New Zealand.
But the constant stream of New Zealanders returning home over the past year has included some who have found the effects of the virus hard to throw off. Returnees may also have had a much harder experience of Covid generally than people living through it here.
The Ministry of Health is seeking proposals for research into the impacts of the condition. Several New Zealand researchers are studying it.
Work will be needed to estimate the likely extent of the problem and the impact on health services. Patients are likely to need specialist assessments and rehabilitation services.
Toronto physiotherapist Adam Brown told the Globe and Mail: "One of the things that just isn't being talked about ... is the ongoing crush of disability that's going to be coming, around people who just can't work and can't do things that they typically could have pre-Covid".
The United States National Institutes of Health estimates between 10 and 30 per cent of those infected with Covid-19 have ongoing symptoms.
Britain's Office of National Statistics has said about one in five people with Covid still have symptoms more than five weeks after their diagnosis. One in 10 still have symptoms at the three-month stage.
CNN analyst Dr Peter Hotez of Texas Children's Hospital believes there will be a major impact on the US economy and its health system. He said people can suffer "post-traumatic stress" from events such as the loss of a family member and pandemic anxieties.
There is good news. Some people in countries with advanced vaccine programmes report symptoms vanishing after being vaccinated.
The Washington Post spoke to a New York therapist Arianna Eisenberg, 34, who suffered from long Covid for eight months. Thirty-six hours after her second vaccine dose, her symptoms were gone.
Survivor Corps, an online organisation of people with ongoing symptoms, also found 171 members said their conditions improved after vaccination.
Akiko Iwasaki, an immunologist at Yale University, said immunisation was likely to help because the vaccines reduce infection.
As more Kiwis return, there will be more people here with damaging experiences of family loss, overwhelmed hospitals, months-long lockdowns, joblessness, and living with daily fears of infection. A New Zealand Covid Long-Haulers Facebook group already has more than 150 members.
Here, the threat has been episodic. There has been far less disruption to our hospital system and the treatments of non-Covid patients than has been the case overseas.
In other countries there have been concerns about cancers going undetected or patients' treatments being delayed.
Some Kiwis have picked up long Covid from infections here, others overseas. We are duty bound to treat them all. And that situation could continue for years.
We may have avoided the worst of its initial impact but will long feel its presence.
