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

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

Written by Marie Ellis on May 2, 2021 — Fact checked by Alexandra Sanfins, Ph.D.

The world is more than a year into 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 are rife, and the common cold has not felt so common. But what will these lifestyle changes do to our health?

Share on PinterestHow have lockdowns affected the immune systems of adults, children, and infants? Maskot/Getty Images

In this article, we 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? For adults and older children, there is some good news: This is not how immunity works.

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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.

Dr. David Strachan first proposed this link in an article that appeared in the BMJ in 1989.

In a paper that appeared in the journal Perspectives in Public Health in 2016, Prof. Sally F. Bloomfield and colleagues examine Dr. Strachan’s original paper.

They write: “The immune system is a learning device, and at birth it resembles a computer with hardware and software but few data. Additional data must be supplied during the first year of life, through contact with microorganisms from other humans and the natural environment.”

They continue:

“If these inputs are inadequate or inappropriate, the regulatory mechanisms of the immune system can fail. As a result, the system attacks not only harmful organisms [that] cause infections but also innocuous targets such as pollen, house dust, and food allergens resulting in allergic diseases.”

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.”

Their paper lays out how the idea that we have become “too clean” has remained in the public mind. 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.”

This is particularly relevant for respiratory viruses such as SARS-CoV-2, which causes COVID-19. Because viruses are not treatable with antibiotics, preventing them with hygiene practices such as washing the hands and cleaning surfaces is paramount.

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

Introduced in 2003, it suggests that 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.”

They note that the most important times in life for OF exposure are during pregnancy, delivery, and the first months of infancy. They also add that 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? Will these behaviors affect the immune responses of young people?

Prof. Bloomfield and colleagues suggest that they will not.

“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.”

They note that 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.

However, the authors also note that “the public idea that obsessive hygiene and cleanliness is the root cause of the rise in allergies is no longer supported.”

Prof. Bloomfield and colleagues conclude their study by noting — and this is the positive news for parents of young children in the times of COVID-19 — “data are now strong enough to encourage […] natural childbirth, physical interaction between siblings and non-siblings, more sport, and other outdoor activities (including babies in prams).”

The takeaway here is that the lockdown walks that have become so popular for families stuck at home are beneficial for introducing infants to those crucial microbes.

Boosting immunity for babies using breast milk

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.

Researchers who published a study in the journal Clinical Immunology in August 2020 note the importance of breast milk for infants born during the pandemic.

This is because it “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.

However, Unicef UK cautions that breastfeeding rates could drop considerably during the pandemic due to a lack of support.

It says: “Many new mothers rely on friends and family to provide support and advice, and professional or voluntary sector services will also be unavailable during this time. As a result, rates of breastfeeding may drop substantially, leading to potential health issues for baby and mom.”

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 Research, 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.

The authors add:

“As the period of time in lockdown and social distancing increases, distress and loneliness will increase; thus, it is likely that the aforementioned changes in the immune system would become more pronounced over time.”

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.


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