T cells ‘remember’ past viral infections
As Dr. tenOever and Dr. Sanjana suggest, another intriguing line of research has found that prior viral infections may prime the body’s immune system to fight COVID-19.
Four other common coronaviruses – aside from SARS-CoV-2 – infect people worldwide, typically causing mild to moderate upper respiratory illnesses like the common cold, says Alessandro Sette, PhD, an infectious disease expert and vaccine researcher with the La Jolla (Calif.) Institute for Immunology.
In a recent study published in Science, he and his team found past infection with these other coronaviruses may give some protection against SARS-CoV-2.
T cells – white blood cells that act like immunological ninjas to ferret out and fight infections – appear to maintain a kind of “biological memory” of coronaviruses they have seen before and can mount an attack on similar pathogens, such SARS-CoV-2, Dr. Sette says.
The new work builds on a prior research he helped lead that found 40%-60% of people never exposed to SARS-CoV-2 had T cells that reacted to the virus – with their immune systems recognizing fragments of a virus they had never seen before.
Dr. Sette says his research shows that people whose T cells have this “preexisting memory” of past coronavirus exposures also tend to respond better to vaccination for reasons not yet well understood.
“The question is, at which point will there be enough immunity from vaccination, repeated infections from other coronaviruses, but also some of the variants of the SARS-CoV-2 … where infections become less frequent? We’re not there yet,” he says.
In addition to these exciting genetic and T-cell findings, other research has suggested low-grade inflammation from allergies – a key part of the body’s immune response to foreign substances – may also give some people an extra leg up, in terms of avoiding COVID infection.
Last May, a study of 1,400 households published in The Journal of Allergy and Clinical Immunology found that having a food allergy cut the risk of COVID-19 infection in half.
The researchers said it’s unclear why allergies may reduce the risk of infection, but they noted that people with food allergies express fewer ACE2 receptors on the surface of their airway cells, making it harder for the virus to enter cells.
The big picture: Prevention still your best bet
So, what’s the takeaway from all of this emerging research?
New York University’s Dr. tenOever says that while genes, T cells and allergies may offer some protection against COVID, tried-and-true precautions – vaccination, wearing masks, avoiding crowded indoor spaces, and social distancing – are likely to provide a greater defense.
He believes these precautions are likely why he and his family have never contracted COVID-19.
“I was tested weekly, as were my kids at school,” he says. “We definitely never got COVID, despite the fact that we live in New York City and I worked in a hospital every single day of the pandemic.”
Ziyad Al-Aly, MD, an infectious disease specialist and director of clinical epidemiology at Washington University in St. Louis, agrees that the new research on COVID-19 is intriguing but won’t likely result in practical changes in the approach to fighting the virus in the near term.
“Getting a deeper understanding of potential genetic factors or other characteristics – that could really help us understand why the virus just comes and goes without any ill effects in some people, and in other people it produces really serious disease,” he says. “That will really help us eventually to design better vaccines to prevent it or reduce severity or even [treat] people who get severe disease.”
In the meantime, Dr. Al-Aly says, “it’s still best to do everything you can to avoid infection in the first place – even if you’re vaccinated or previously infected, you should really try to avoid reinfection.”
That means sit outside if you can when visiting a restaurant. Wear a mask on a plane, even though it’s not required. And get vaccinated and boosted.
“In the future, there may be more tools to address this pandemic, but that’s really the best advice for now,” Dr. Al-Aly says.
A version of this article first appeared on WebMD.com.