New Zealand hospitals are experiencing the payoff of “immunity debt” created by Covid-19 lockdowns, with wards flooded by babies with a potentially-deadly respiratory virus, doctors have warned.
Wellington has 46 children currently hospitalised for respiratory illnesses including respiratory syncytial virus, or RSV. A number are infants, and many are on oxygen. Other hospitals are also experiencing a rise in cases that are straining their resources – with some delaying surgeries or converting playrooms into clinical space.
RSV is a common respiratory illness. In adults, it generally only produces very mild symptoms – but it can make young children extremely ill, or even be fatal. The size and seriousness of New Zealand’s outbreak is likely being fed by what some paediatric doctors have called an “immunity debt” – where people don’t develop immunity to other viruses suppressed by Covid lockdowns, causing cases to explode down the line.
Epidemiologist and public health professor Michael Baker used the metaphor of forest brushfires: if a year or two have passed without fire, there is more fuel on the ground to feed the flames. When a fire finally comes, it burns much more fiercely. “What we’re seeing now is we’ve accumulated a whole lot of susceptible children that have missed out on exposure – so now they’re seeing it for the first time,” Baker said.
The “immunity debt” phenomenon occurs because measures like lockdowns, hand-washing, social distancing and masks are not only effective at controlling Covid-19. They also suppress the spread of other illnesses that transmit in a similar way, including the flu, common cold, and lesser-known respiratory illnesses like RSA. In New Zealand, lockdowns last winter led to a 99.9% reduction in flu cases and a 98% reduction in RSV – and near-eliminated the spike of excess deaths New Zealand usually experiences during winter.
“This positive collateral effect in the short term is welcome, as it prevents additional overload of the healthcare system,” a collective of French doctors wrote in a May 2021 study of immunity debt. But in the long term, it can create problems of its own: if bacterial and viral infections aren’t circulating among children, they don’t develop immunity, which leads to larger outbreaks down the line.
“The lack of immune stimulation… induced an “immunity debt” which could have negative consequences when the pandemic is under control and [public health intervientions] are lifted,” the doctors wrote. “The longer these periods of ‘viral or bacterial low-exposure’ are, the greater the likelihood of future epidemics.”
New Zealand has reported nearly 1,000 RSV cases in the past five weeks, according to the Institute of Environmental Science and Research. The usual average is 1,743 over the full 29-week winter season. Australia is also experiencing a surge, with overcrowded Victoria hospitals also hit by unusually high rates of RSV.
Peaks like the current outbreak don’t necessarily mean the country will have more RSV cases overall, Baker says – it may just be that all the cases are grouped together, instead of spread out over several years. But even that can cause major problems. “If you get a big peak it can overwhelm your health system, or put real pressure on it, which we’re seeing with RSV,” Baker said.
The current outbreak is already stretching New Zealand’s hospitals. At Middlemore hospital in Auckland, a playroom has been converted into a clinical space with 11 special care baby cots. Health boards in Auckland and Canterbury have postponed surgeries to divert resources into children’s wards. A number of hospitals have asked children under 12 not to visit, to try to avoid spreading the virus. John Tait, chief medical officer for the Wellington area’s district health boards said the region had 46 children hospitalised, including two in intensive care. Those numbers were “continually changing as patients are discharged and others admitted,” he said.
Usually, people experience near-universal exposure to RSV as children, Baker said, with most exposed in their first year of life.
“If you remove that exposure for a period then you will have a bigger cohort of unexposed children, and therefore – as you can see we have happening at the moment – it can sustain a much bigger outbreak when they are eventually exposed to the virus.”
While RSV is a common cause of winter hospitalisation of children, elderly people and people with suppressed immune systems are also vulnerable. New Zealand’s director-general of health, Dr Ashley Bloomfield, said he was “certainly concerned about the sharp surge in RSV cases”.
“We had very little RSV last year,” he said. “There’s some speculation that [the current outbreak] may be partly exacerbated by the fact we didn’t have any last year and so there is a bigger pool of children who are susceptible to it.”