Why diseases are behaving in ‘peculiar’ ways after Covid-19

Experts have revealed the reason that a spate of diseases we haven’t seen since 2020 are now behaving in “new and peculiar” ways.

After two long years, the Covid-19 pandemic has eased in much of the world, alongside the many social restrictions implemented to slow its spread, as people return to a pre-lockdown way of life.

But experts in the US and UK have warned that in its place, a series of viruses, from the “super flu” to tuberculosis and monkeypox, have emerged that are behaving “in new and peculiar ways” – and the pandemic could be to blame.

Take monkeypox – a rare, viral infection typically found in Central and West Africa that has baffled health experts in recent weeks as it’s emerged in 29 non-endemic countries, including Australia.

“Patients are presenting differently than we were previously taught,” associate medical director for infection prevention at Yale New Haven Hospital, Dr Scott Roberts, told CNBC this week.

“There’s a lot of unknowns that do make me uneasy. We are seeing very atypical behaviours in a number of ways for a number of viruses.”

Or the flu – where in the US, but also in Australia, cases have climbed as Covid restrictions were stripped back after two of the mildest flu seasons on record.

“We’ve never seen a flu season in the US extend into June,” Dr Roberts said.

“Covid has clearly had a very big impact on that. Now that people have unmasked, places are opening up, we’re seeing viruses behave in very odd ways that they weren’t before.”

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‘Now that people have unmasked, places are opening up, we’re seeing viruses behave in very odd ways.’ Picture: NCA NewsWire/David Geraghty

Reported cases of the flu increased in Australia a month before the seasonal reporting period even began. Picture: NCA NewsWire/David Geraghty

Here, the illness increased a month before the seasonal reporting period even began, with the Australian Influenza Surveillance Report revealing that for the past two months, the number of confirmed flu cases per week has exceeded the five-year average.

“Over the past two years influenza cases were very low in Australia because of limitations on international travel and a range of other measures such as social distancing and mask wearing, but with restrictions now eased, influenza cases are rising,” acting chief medical officer Dr Sonya Bennett told reporters earlier this week.

Speaking to news.com.au, Deakin University chair in epidemiology Catherine Bennett said that “it’s less about Covid-19 itself, and more about how our public health responses to Covid-19 have also impacted our exposure to other infectious diseases, and our immunity”.

“We have enjoyed two years with lower infection rates than usual which has been good while it lasted, but with that we have lost some of our natural immunity as we haven’t been exposed to these viruses,” Professor Bennett said.

“And [we] may have also dropped our flu vaccination uptake – so not had the booster dose in the last couple of years – [which] will also mean we are that bit more vulnerable, and flu infections might lead to more severe symptoms than before.”

Since 2020, restrictions put in place to limit the spread of Covid had the same effect on other illnesses.

“All restrictions and precautions put in place to reduce our contact with others outside our own household have helped reduce our exposure to other respiratory infections in particular, and therefore also reduced the boosting to our immune systems that comes with that,” Prof Bennett said.

“If you are constantly exposed to colds and flus, you will boost your immunity each time you successfully fight off an infection or recover from one.

Covid restrictions also helped reduce the spread of other illnesses. But now they are back. Picture: iStock

“Any short-term impacts [on our] immune systems – such as less physical activity or lower vitamin D with the extra time spent indoors in the pandemic, especially in Melbourne where there were longer restrictions in place – will probably have reduced over the summer, so the concern regarding infections this winter is likely to be largely driven by the low infection rates in 2020 and 2021.”

As the weather turns colder, Prof Bennett said: “We should be aware that we are more at risk of both a wider range of infections, and that we might feel more unwell with them than in previous years, especially young children who have not experienced a ‘normal’ winter from an infectious disease point of view.

“There has also been some concern that high rates of Covid and the flu together might mean more people are seen with both at the same time, and this might lead to a more marked illness,” she said.

Australians have been urged to book in their flu vaccines as temperatures plummet. Picture: NCA NewsWire/David Crosling

But, at least where diseases like monkeypox are concerned, infectious disease specialist at Sheba Medical Centre, Eyal Lesham, told CNBC it’s important to note that greater surveillance and awareness of public health issues in the wake of the pandemic could make outbreaks seem more prevalent than they actually are.

“The general population and the media have become much more interested in zoonotic outbreaks and infectious diseases,” Professor Lesham said.

“It’s not that the disease is more prevalent, but that it gets more attention.”

Now that these diseases are circulating, though, Prof Bennett said that “it does still pay to try to avoid infection” by taking care of your overall health and still enacting preventive measures (like handwashing and mask wearing) in certain situations.

“If you end up being exposed, by wearing a mask you have reduced the number of virus particles that get into your system, [and] then you have a better chance of beating off the infection without becoming unwell, and boosting your immunity at the same time,” she said.

“We are unlikely to have the same combination of international border closures and strict internal controls in place again, and so we must now recognise these old infection risks are back.

“But hopefully one legacy of Covid will be that we realise the value of masks, and that it isn’t necessary to suffer a cold or two every winter.”

Originally published as Why diseases are behaving in ‘peculiar’ ways after Covid-19