IT IS a question high in the minds of many parents and carers of infants born during the first years of the covid-19 pandemic: have lockdowns and social distancing had a long-term effect on babies' health? The good news is that these concerns are largely underpinned by misunderstandings over how the immune system is shaped during our first years of life.
It is clear that pandemic public health measures have had an impact on children's exposure to bacteria and viruses that cause illness. When strict social distancing rules were in place, the capacity for infections to spread was dramatically reduced.
An analysis of data from across England found that the number of children below the age of 15 admitted to hospital with influenza between March 2020 and June 2021 dropped by 94 per cent. It wasn't just flu that was affected: the analysis found reductions in child hospitalisations in 18 of the 19 infections they looked at, including mumps, measles, croup, tonsillitis and bronchiolitis.
Fewer infections
This leaves lockdown babies in a different position to the average infant. Typically, around 90 per cent of UK children have had an infection by the age of 1, for instance, but an analysis of babies born during Ireland's first lockdown found that less than half of 12-month-olds experienced any infections during their first year.
Fortunately, we don't actually need to get sick when we are very young. Infections like flu are more likely to lead to serious complications, such as pneumonia, in young children, especially those under the age of 2. “If you can avoid disease, it's better if you avoid it,” says Nikolaos Papadopoulos at the University of Manchester, UK.
In recent months, the northern hemisphere has had a difficult winter in terms of seasonal infections, including among children. Lower population immunity is partly to blame for surging levels of illness caused by pathogens like the flu virus and RSV: because there were fewer cases of these illnesses during strict covid-19 measures, numbers are catching up now. This isn't a sign that children's immune systems have been weakened by lockdowns.
The idea that it is important to get infections during infancy comes from the hygiene hypothesis, first proposed by epidemiologist David Strachan in 1989. The thinking was that life had become more hygienic, leading children to catch fewer infections, and that this predisposed them to develop allergies. But while the idea that young immune systems need to be “trained” on pathogens has taken hold in the public consciousness, the hygiene hypothesis isn't our best way of understanding immune systems in the modern age. What we really need in early life is to encounter a wide diversity of microbes – and not just the ones that are bad for you.
The ideal scenario, says Papadopoulos, is to be exposed “in very small quantities to many different types of microbes, viruses and bacteria, below the threshold for disease”. So, rather than being a good thing in itself, getting ill is more of a marker that your child is encountering a range of microbes, good and bad. If you don't encounter many pathogens in your first years, that doesn't mean you will be less good at fighting them off later on, because your immune system continues to learn about diseases throughout life.
However, our early years do seem to be important for shaping our response to allergens, and a lack of exposure to diverse microbes during this time may make children more susceptible to allergies, asthma and some types of eczema. The Irish study found that lockdown babies were more likely to have atopic eczema and show signs of sensitisation to egg – the first step towards an allergy – although there was no increase in the proportion of children who actually had an egg allergy by the age of 1.
However, there are other ways we receive early microbial exposure than just socialising. Some, such as being born vaginally rather than by C-section, may not have been affected by the pandemic. Others, such as breastfeeding, spending time outside, antibiotic use and even living with a pet dog, may have been influenced by the way our lives changed in 2020 and 2021 –positively for some, negatively for others.
At the same time, while we know that all these factors seem to be linked to immune functioning, none of them has a strong enough effect to fully determine your immune future. It will be shaped by a complex interplay of personal circumstances, including genetics and many small and unique differences in the microbial environments in which we grow up. Which, thankfully, means there is no “right” way to train a young immune system.
The average person should expect one or two mild illnesses a year