In a new study from La Jolla Institute for Immunology, researchers found that four COVID-19 vaccines (Pfizer-BioNTech, Moderna, J&J/Janssen, and Novavax) prompt the body to make effective, long-lasting T cells against SARS-CoV-2.
These T cells can recognize SARS-CoV-2 Variants of Concern, including Delta and Omicron.
These data come from adults who were fully vaccinated, but not yet boosted.
The researchers are now testing T cell responses in boosted individuals and people who have experienced “breakthrough” COVID-19 cases.
The study also shows that fully vaccinated people have fewer memory B cells and neutralizing antibodies against the Omicron variant.
This finding is in line with initial reports of waning immunity from laboratories around the world.
Without enough neutralizing antibodies, Omicron is more likely to cause a breakthrough infection.
Fewer memory B cells means the body will then be slower to churn out additional neutralizing antibodies to fight the virus.
The good news is that neutralizing antibodies and memory B cells are just two arms of the body’s adaptive immune response.
In a person exposed to SARS-CoV-2, T cells do not prevent infection. Instead, T cells patrol the body and destroy cells that are already infected, which prevents a virus from multiplying and causing severe disease.
The team believes the “second line of defense” from T cells helps explain why Omicron infections are less likely to lead to severe disease in fully vaccinated people.
The current COVID-19 vaccines were designed to teach the immune system to recognize specific epitopes on the initial “Alpha” variant of SARS-CoV-2.
As the virus has mutated, its architecture has changed, and the concern is that immune cells will no longer recognize their targets.
The new study shows that while the architecture of Omicron is different enough to evade some neutralizing antibodies and memory B cells, memory T cells still do a good job of recognizing their targets, even on the highly mutated Omicron variant.
Overall, at least 83% of the CD4+ (helper) T cell responses and 85% of the CD8+ T cell responses stayed the same, no matter the vaccine or the variant.
Vaccinated people have memory CD4+ T cells, CD8+ T cells, and memory B cells to help fight the infection if the virus gets past the initial antibodies, and having multiple lines of defense is likely an important strength.
The researchers emphasize that no one should count on T cell protection alone.
The study sheds light on immunity at the population level, but individual immune responses vary, and relying on one’s untested immune system to fight COVID is a roll of the dice.
The team urges people to still be cautious and keep wearing masks. They also emphasize the importance of getting a booster.
If you care about Omicron, please read studies about do at-home COVID-19 tests detect omicron, and what you need to know Omicron and COVID boosters.
For more information about health, please see recent studies about people infected with Omicron less likely to get Delta infection, and results showing that Omicron may be less likely to cause severe disease.
The study is published in Cell. One author of the study is Alessandro Sette.
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