Viruses can take a toll on our health in the long-term, sometimes in ways which may not even become obvious until many years later, medical experts warn. Photo: 123rf.com / Composite Image - RNZ
Covid infections are putting people at higher risk of diabetes, strokes, heart disease and other long-term illnesses - but experts warn it may be decades before the full impact is known.
Meanwhile, could Covid-19 also be blamed for the increased frequency and severity of colds and flu? Has it damaged our ability to fight off infections?
Northland emergency doctor Gary Payinda said some viruses, which used to cause barely a sniffle in healthy adults, were now putting people in hospital.
"We're now seeing your typical regular healthy middle-aged person presenting to ED with bad cases of RSV. And that's pretty novel for us," Payinda said.
He suspected Covid may have damaged people's immunity in subtle ways that fell below the threshold to qualify as long Covid.
Several international studies - involving millions of people, mainly from before vaccines became widely available - found a Covid infection doubled the risk of developing heart disease and increased the chance of stroke 1.6 fold.
It was also associated with higher rates of both type 1 and type 2 diabetes.
"There are a lot of long-term sequelae to Covid that we don't really know yet and we may not know for years," Payinda said.
"Post polio syndromes were not identified for literally decades after polio infections. The same with the 1918 flu epidemic - people born during the 1918 Spanish flu epidemic had a two- to three-fold increased risk of later developing Parkinson's Disease."
The latest research showed vaccination halved the risk of cardiac problems post-infection, he said.
Auckland University immunologist Anna Brooks said our immune systems had been exposed to a novel virus, which caused inflammation of the blood vessels.
"And we still don't know the broad spectrum impacts of that ... including on healthy, recovered people.
"We don't say that to be alarmist, we say it from the point of view that we need to better understand the impacts. We may have different responses to viruses we've seen before, we may respond differently to vaccines."
A survey by Business New Zealand and Southern Cross Health Insurance found sick days hit a record high in 2022: people were sick an average of 5.5 days during the year, compared with a range of 4.2 and 4.7 days between 2012 and 2020.
That cost the economy $2.86 billion, compared to the $1.85b indicated by the survey in 2020.
Employers and Manufacturers Association head of advocacy Alan McDonald said it was difficult to tell whether people were getting sick more often, or if they were just staying home when sick.
"That's probably on the back of going to 10 days sick leave as well," McDonald said.
Minimum sick leave entitlements were increased by a law change from five to 10 days a year, in 2021.
"So [people are taking that] precautionary approach, so more and more people are aware that if you have a sniffle or a bit of a cough to just stay home - not just for your own good, but the good of those around you," McDonald said.
However, Payinda said employers - including schools and hospitals - should be doing more to ensure clean air by providing CO2 monitors and adequate ventilation.
"Employers are talking about the inordinate numbers of employees that they have out sick due to repeated respiratory infection. Yet they're doing almost nothing to protect their employees from repeated respiratory infection.
"I guess the message from people like me would be: it's not a good idea to subject yourself to unnecessary repeat infections from something that could do short and long-term damage to your body.
"So I think we need to be doing a much better job of ensuring we have clean air in workplaces, schools and hospitals as well."
Dr Brooks said re-infections could also trigger long Covid, as her colleagues overseas were reporting.
"People are turning up at long Covid clinics and saying: 'No one told me that my fourth or fifth infection could cause this'.
"Covid is not done with us. We might be done with it, and our pandemic emergency response may be over but the pandemic nature of this virus is certainly not over.
"And immunologically is where we are still sinking our teeth in and saying there's so much more we need to know."
Dr Brooks hoped people would adopt "a new normal" and continue to use masks in crowded situations and "avoid breathing in each other's viruses".
"Yes we're bored of Covid and everyone is over it, but it's still there," Dr Brooks said.
"It needs to be part of the norm, because ignoring it doesn't make it go away."