An unsung arm of the immune system appears to protect against severe disease with the omicron variant even when antibodies wane, helping to explain why a record wave of infections hasn’t engulfed hospitals so far.

T cells, the body’s weapon against virus-infected cells, were primed enough by vaccination that they defended against omicron in separate studies from Erasmus University in the Netherlands and the University of Cape Town in South Africa.

The findings could help explain why the wave of omicron cases hasn’t so far caused a surge in mortality from South Africa to the U.S. and the U.K. Unlike antibodies, T cells can target the whole of the virus’s spike protein, which remains largely similar even in the highly mutated omicron.

The Dutch researchers looked at 60 vaccinated health-care workers and found that while their antibody responses to omicron were lower or nonexistent compared with the beta and delta variants, T cell responses were largely unaltered, “potentially balancing the lack of neutralizing antibodies in preventing or limiting severe Covid-19.”