Moderna, Pfizer COVID Vaccines Activate Key Immune System Players, Despite Variants

TUESDAY, July 6, 2021 (HealthDay News) -- Key immune system cells in folks who've had COVID-19 or the Moderna and Pfizer vaccines are able to recognize and mount a defense against highly contagious coronavirus variants, new research shows.

In both groups, CD4+ "helper" T-cells and CD8+ "killer" T-cells can recognize the Delta mutation and three other widespread variants of concern.

That's key to the immune system's ability to kill infected cells and stop severe infections, researchers from the La Jolla (Calif.) Institute of Immunology explained.

The Moderna and Pfizer COVID vaccines are two of three approved for use in the United States. The third — the Johnson & Johnson vaccine — wasn't included because it wasn't available when the study began. But the company announced Thursday that preliminary research shows the vaccine is effective against the Delta variant.

The Pfizer/Moderna findings were published July 1 in the journal Cell Reports Medicine.

"This study suggests that the impact of mutations found in the variants of concern is limited," said senior author Alessandro Sette, of the institute's Center for Infectious Disease and Vaccine Research. "We can presume that T-cells would still be available as a line of defense against viral infection."

Researchers noted that their study only examined how T-cells respond to variants of concern, and that several are associated with lower levels of virus-fighting antibodies.

"These variants are still a concern, but our study shows that even if there is a decrease in antibodies, as other studies have shown, the T-cells remain largely unaffected," said study co-author Alba Grifoni, an instructor at the institute. "The vaccines still work."

Co-author Shane Crotty said the findings highlight the importance of enlisting T-cells to fight the new coronavirus.

"COVID vaccines do a fantastic job of making antibodies that stop SARS-CoV-2 infections, but some of the vaccines do less well at stopping infections from variants," he said in an institute news release.

"You can think of T-cells as a backup system: If the virus gets past the antibodies -- if you have vaccine T-cells -- the T cells can probably still stop the variant coronavirus infection before you get pneumonia," said Crotty, a professor at the institute.

Research is underway to take advantage of the apparent flexibility in T-cell response.

For example, Grifoni said, it may be possible to develop booster shots that could increase immunity by prompting the body to produce more antibodies against coronavirus variants and/or by adding additional parts of the virus recognized by T-cells.

More information

The U.S. Centers for Disease Control and Prevention has more on coronavirus variants.

SOURCE: La Jolla Institute for Immunology, news release, July 1, 2021