Question: I’ve read that COVID can disrupt the immune system and make people more susceptible to other infections. Is this the reason why hospitals have been swamped with so many cases of flu and RSV (respiratory syncytial virus), especially among children?
Answer: The theory that a COVID-19 infection might cause some type of immune dysfunction is being seriously considered by medical experts.
“This is a bit of an evolving story,” explained Fahad Razak, a professor in the Temerty Faculty of Medicine at the University of Toronto.
“There are a lot of things we are still learning about COVID and it will take time to fill in the details,” added Dr. Razak, who is also an internal medicine physician at St. Michael’s Hospital in Toronto. “So, it remains an open scientific question right now.”
One reason researchers think that COVID could alter immune responses is because it’s well known that this happens with some other common viruses.
For instance, influenza can compromise your ability to deal with bacteria and increases the risk of developing bacterial pneumonia, said Dawn Bowdish, a professor of medicine and a Canada Research Chair in aging and immunology at McMaster University in Hamilton. “In the 1918 to 1919 influenza pandemic, more people died of bacterial infections than from the actual flu virus.”
Measles can essentially wipe out immune memory. “It is almost like going back to being a baby again where all the immune experiences that you developed throughout your life disappear,” said Dr. Bowdish.
However, she is quick to emphasize that COVID is not like measles: “It doesn’t eliminate immune memory.”
Studies done on blood samples from infected adults show that COVID does produce measurable effects on the immune system. In some, a COVID infection is associated with either an increase or a decrease in certain types of immune cells, including neutrophils and naive T-cells, which play important roles in guarding against new infections.
Most studies find that these immune changes are temporary and last for less than a year, said Dr. Bowdish. In people with long COVID, they may last longer.
A recent study from Israel found that young people who’ve had COVID-19 are at elevated risk of getting strep throat (Streptococcal tonsillitis) and pink eye (conjunctivitis) for several months. “This is the first indicator that COVID-19 infections might also increase the risk of bacterial infections,” said Dr. Bowdish.
Epidemiological research, which looks at health trends in the population, has also produced some intriguing results. One study found that people are likely to have more doctor appointments, be prescribed more antibiotics and have more abnormal blood tests results in the year following a bout of COVID.
But it is still uncertain what these immune changes and epidemiological observations actually mean. “It is difficult to link these things to an increased risk of RSV or influenza,” said Dr. Bowdish.
In the absence of clear answers, doctors are concerned about misinformation and far-fetched theories circulating on social media where some claim that COVID causes permanent harm.
“The premise that COVID leads to widespread immunosuppression is simply not correct,” said Angela Rasmussen, a virologist and adjunct professor in the department of biochemistry, microbiology and immunology at the University of Saskatchewan. “The changes we see in some immune cells are transient and new ones are constantly being regenerated,” she added.
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With more research, we may find that COVID has no significant and durable impact for most individuals in their overall risk of catching other infections. And, if that is the case, various factors could account for the surge in hospital admissions in recent months.
Dr. Razak thinks there is a fairly simple explanation for the elevated levels of RSV infections. He noted that most children normally catch this illness early in life and develop some protection against subsequent infections.
During the initial years of the pandemic, however, many toddlers were shielded from RSV because of the introduction of public health safeguards, such as masking, social distancing and daycare closures.
Now that COVID-containment measures have been relaxed, these children, as well as those born after them, are being exposed to RSV. “It’s like a double cohort of children getting RSV at the same time,” said Dr. Razak. And that has meant a larger number of kids have needed medical care compared with a typical year before the pandemic.
To further complicate matters, flu vaccination rates are down for a variety of reasons, ranging from pandemic-related health care disruptions to vaccine hesitancy.
Dr. Bowdish noted that pregnant women are urged to get the annual influenza shot. The protection they gain from the inoculation is passed on to their infant. So, if moms-to-be skip the shot, their offspring could face an increased risk of flu complications.
For Dr. Rasmussen the recent surges in hospitalizations send home a clear message: “We need to increase vaccination rates.”
There isn’t a vaccine for RSV but this year’s flu shot is a good match for the influenza strains currently circulating. And the COVID bivalent boosters, designed to guard against the original version of the virus and the Omicron variant, provide enhanced protection against developing severe disease.
By keeping flu and COVID patients out of hospitals, it will free up resources for treating other urgent cases.
“If you are not up-to-date on either your COVID booster or your flu vaccine, go out and get it now,” said Dr. Rasmussen. “This is the single most important thing you can do to reduce your own risk – and the risk to others.”
Paul Taylor is a former Patient Navigation Adviser at Sunnybrook Health Sciences Centre and former health editor of The Globe and Mail.