Why does COVID-19 strike some and not others? Fauci sees answer in study
WASHINGTON
Dr. Anthony Fauci, the nation’s leading infectiousdisease expert, said a new study could explain the different outcomes that people experience with the SARSCoV-2 coronavirus. Some people have no symptoms or a mild case while others are hospitalizated or die.
The discovery, which found potential signs of immunity in people who had previously been exposed to other types of coronaviruses, could also expand the hunt for a long-lasting vaccine for SARS-CoV-2, which causes COVID-19.
Fauci and other scientists said the study published in Science this month held promising findings for understanding why some individuals exposed to COVID-19 for the first time have a modest reaction to the virus.
The study found that the immune systems of roughly half of its subjects appeared to remember past exposure to other, prevalent coronaviruses, including variants of the common cold, equipping them to respond more quickly to a COVID-19 infection.
The findings also offer new insights that could help in developing a vaccine by looking at T cells, which help fight the virus.
Currently, all major candidates for a coronavirus vaccine undergoing clinical trials focus on harnessing a single antibody protein that can neutralize the virus.
Since the coronavirus outbreak began, scientists have struggled with the question of why SARS-CoV-2 hits some people so hard and leaves others unscathed.
“One of the things that I don’t think has been emphasized very much at all during the attempt to address, scientifically, the COVID-19 outbreak, and vaccine development and testing, is that we’ve been focusing very exclusively on the antibody test,” Fauci told McClatchy in a recent interview. “There’s another equally important component of the immune system.”
The study — funded by the National Institute of Allergy and Infectious Diseases, which Fauci heads — is one of the first to identify T cell “cross reactivity” in individuals who have previously been exposed to one of the four endemic coronavirus strains, SARS or MERS.
T cells, which originate in the thymus, serve as a secondary line of defense in the immune system once antibodies have failed or faded away.
“If you look at it metaphorically as an army with different levels of defense, the antibodies prevent the virus from getting in. So that’s kind of like the first line of defense,” Fauci explained. “For those viruses that do escape and infect some cells, the T cells come in and kill the cells that are infected or block them.”
The T cells of individuals who took part in the study recognized SARS-CoV-2 when it was introduced to their immune systems for the first time.
Angela Rasmussen, a virologist at Columbia University, also explained the immune system in military terms, likening antibodies to infantry and T cells to cavalry.“None of our soldiers have been trained before this,” Rasmussen said. “But the T cell finding suggests that, maybe the cavalry actually is prepared for this virus. Maybe they already know a little bit about how to fight it. And maybe that’s helping the overall army stave off the invading virus.”
Rasmussen cautioned against overstating the findings of the study, noting that the level of protection among those with T cell memory from other coronaviruses remains unknown. But she celebrated the findings.
“It’s a piece of good news, scientifically, because otherwise we’re completely naive to this virus and it’s completely brand new,” Rasmussen said. “If there’s anything that can give us an edge in fighting it, even within our own bodies and immune systems, that to me is great news and is very promising.”
Fauci noted that, while T cells last much longer than antibodies, they do not last forever. The more recently an individual was infected with another type of coronavirus, the greater likelihood of some protection from COVID-19.
It may explain the vast differences within older age groups, where scientists have tracked both asymptomatic cases as well as deaths in large numbers.
While one elderly individual might have been exposed to a common coronavirus within the past few years, another might not have had that exposure for decades — and not have the T cell memory that might otherwise provide protection.