How have COVID-19 pandemic lockdowns affected our immune systems?

It’s been over a year since the COVID-19 pandemic, so many people have been living with lockdown restrictions, quarantine periods, and physical distancing for an extended period of time. Hand sanitizer and masks have become a necessity, and the common cold has not felt so common. But what will these lifestyle changes do to our health?

We will look at what effect living physically distanced from other people might have on the immune systems of adults, children, and infants born during the pandemic. Some people have voiced concerns over whether their immune systems are being challenged, given that the general public is no longer physically mixing. Might our immune systems consequently “forget” how to fight off disease-causing agents?

According to MIT Medical, by the time a person reaches adulthood, their immune system has already had exposure to plenty of bacteria and viruses and is able to mount an attack against these invaders. Because of this, the immune system has already learned how to destroy these microbes and will not forget, even in the wake of long-term lockdowns. But what about younger children, whose immune systems are still in the learning phase?

Children and the ‘hygiene hypothesis’

Many parents and caregivers will be familiar with the so-called hygiene hypothesis even if they do not know it by name. It is essentially the idea that there is a link between the rise in allergic conditions and reduced exposure to microbes during childhood resulting from hygiene measures, such as frequent hand washing, introduced to protect children from infection.

Prof. Jonathan Hourihane, from the RCSI University of Medicine and Health Sciences in Dublin, Ireland, adds that the increases in eczema, asthma, hay fever, and food allergies over the past 30 years have likely resulted from decreased exposure to infections.

“We want to see children playing on the floor, getting dirty, and being exposed to lots of people in lots of environments,” he says. “The outcome of this is usually a strong immune system, linked to a healthy population of gut bacteria, called the microbiome.”

With this in mind, should parents of infants or young children be concerned about the effects of physical distancing and lockdowns on their immune systems?

Yes and no.

Some microbes are friends, others are not

Prof. Bloomfield and colleagues write that while “evidence supports the concept of immune regulation driven by microbe-host interactions, the term ‘hygiene hypothesis’ is a misleading misnomer. There is no good evidence that hygiene, as the public understands, is responsible for the clinically relevant changes to microbial exposures.”

Writing in 2016, Prof. Bloomfield and team prophetically note that this is also “happening at a time when infectious disease issues mean that hygiene is becoming more, rather than less, important.”

The authors point to the post-hygiene hypothesis theory known as the old friends (OF) mechanismTrusted Source.

Respiratory viruses such as SARS-CoV-2, which causes COVID-19. Viruses are not treatable with antibiotics, preventing them with hygiene practices such as washing the hands and cleaning surfaces is paramount.

The important exposures to microbes in early life are not actually colds, measles, or other childhood ailments, but rather those microbes that were already around during the hunter-gatherer period, when the immune system was evolving.

These microbes include species that live in both indoor and outdoor environments, and they come from the skin, gut, and respiratory tracts of other people.

“OF exposures are vital,” say the researchers, “because they interact with the regulatory systems that keep the immune system in balance and prevent overreaction, which is an underlying cause of allergies. Diversity of microbial exposure is key.”

The most important times in life for OF exposure are during pregnancy, delivery, and the first months of infancy. Also, continuing exposure from the mother and siblings is vital.

Likewise, having pets increases the overall diversity of microbes in the home.

Hand sanitizer: friend or foe?

What about all the hand washing and sanitizing?

“The idea that we could create ‘sterile’ homes through excessive cleanliness is implausible; as fast as microbes are removed, they are replaced, via dust and air from the outdoor environment, […] commensal microbes shed from the human body and our pets, and contaminated foods brought into the homes.”

Changes in lifestyle and environment, including dietary changes and increased antibiotic use, as well as accelerated urbanization have all led to changes in our microbe exposure. This has likely contributed to the increase in allergic conditions such as eczema, hay fever, and food allergies.

Lockdown walks that have become so popular for families stuck at home are beneficial for introducing infants to those crucial microbes.

If a person is able to breastfeed their child or get access to donated breast milk to feed them, this would also be beneficial — particularly in the absence of usual contact with more people and, therefore, more diverse microbes.

Breast milk “contains not only the basic nutrients (proteins, carbohydrates, and fats) but also a multitude of factors that drive development and maturation of the immune system and protect newborns from the environmental pathogens.”

They add that breast milk also contains immune cells such as lymphocytes, neutrophils, and macrophages, further boosting immunity.

The psychological effects of isolation on immunity

Having explored the physical aspects of immunity, we now turn our focus to the psychological effects. 

Although adults and older children can breathe a sigh of relief knowing that their immune systems will remember how to fight off microbes, there is another piece of this puzzle to consider: stress.

Researchers Fulvio D’Acquisto and Alice Hamilton, who published a review in the journal Cardiovascular ResearchTrusted Source, note that while physical distancing “minimizes the spread of COVID-19, such social isolation has the potential to affect the cardiovascular and immune systems.”

They point to previous animal studies that researchers conducted in socially isolated mice, primates, and other species.

They write: “Of note, high levels of inflammation are a driver for [cardiovascular disease]. Social isolation was linked to downregulation of type I and II interferons and an impaired response to infection by simian immunodeficiency virus.”

They note that in the wake of social isolation, it is the emotional rather than the physical separation that is the triggering factor in the body’s reduced ability to respond to adversity. 

Researchers have also observed such effects in humans. 

According to a paper by Stanford researcher Firdaus S. Dhabhar, Ph.D., in the journal Immunologic Research, “chronic stress can suppress protective immune responses and/or exacerbate pathological immune responses.”

For adults, it is the stress of isolation and the pandemic, rather than the lack of interaction with microbes, that is a concern for the immune system.

Older children and immunity

Older children have faced unique challenges since March 2020, and several research teams are focusing on how these challenges may affect immunity for this age group.

A survey that researchers conducted in Canada and published in the International Journal of Behavioral Nutrition and Physical Activity analyzed the changes in movement and play behaviors in children immediately following the COVID-19 outbreak.

The results showed that only 4.8% of children and 0.6% of youths were meeting the combined movement behavior guidelines during this time. 

Both children and youths had lower physical activity levels, spent less outside time, had higher leisure screen time, and got more sleep overall during the survey period.

The researchers note that healthy movement behaviors positively contribute to both the physical and mental health of young people, including the development of stronger immune systems. Therefore, these initial findings present some cause for concern.

The authors do note that family dog ownership and parental encouragement and support were positively linked to healthy movement behaviors.

Meanwhile, another survey — this time by the Children’s Commissioner’s Office in the United Kingdom — set out to understand how school-age children were experiencing stress during the initial lockdown period.

Researchers conducted surveys of around 2,000 school children aged 8–17 years in England in March and June 2020 to gauge the causes and frequency of their stress during lockdown.

Interestingly, they found that as lockdown progressed, many children felt stressed less often. Specifically, between March and June 2020, the percentage of children who felt stressed some of the time decreased from 47% to 34%, and the percentage of children who felt “rarely or never stressed” increased from 23% to 42%.

Based on survey response answers, the researchers speculate that the reason for the children’s stress levels decreasing during this period is that little, everyday worries went away during lockdown. Answers to the question, “What makes you feel stressed?” changed from the first survey to the second.

In the first survey, answers typically involved school, crowds, worries about their appearance, bullying, and allergies. In the second survey, such worries were absent, and their answers primarily focused on COVID-19.

It is not all good news on the stress front, however, as the survey also revealed that the greatest reported increase in stress during the lockdown period came from worries about school. 

Just over 40% of children said that they felt more stressed about their schoolwork and exams while schools were closed.


For adults, children, and infants alike, getting outside and taking walks or engaging in other types of physical activity is beneficial for the immune system. For adults and older children, getting fresh air and physical activity will likely help mitigate the effects of stress on immunity. For infants, having exposure to OF microbes outside will help contribute to the development of a robust immune system.

There are studies currently underway that are looking at what effect the pandemic is having on infants born during this period. The researchers will look at whether the decreased viral infection rate and improved air quality that resulted from the lockdown will make allergic conditions more or less common among infants whose families have experienced isolation and physical distancing.

As with many aspects of this pandemic, however, any definitive conclusions on this front are still to come. In the meantime, it is probably best to keep that hand sanitizer within arm’s reach.

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