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At a World Health Organization meeting on Wednesday, scientists offered some encouraging findings about immunity against the fast-spreading Omicron variant of the coronavirus. Several laboratory studies suggest that so-called T cells in vaccinated people can put up a strong defense against the variant, which could help prevent severe disease, hospitalization and death. The findings are a welcome departure from a torrent of worrying new data about Omicron. The variant’s mutations enable it to evade many of the antibodies produced either by vaccination or infection with previous variants. But antibodies are not the only important player in a person’s immune response to the virus. “The good news is that T cell responses are largely maintained to Omicron,” said Wendy Burgers of the University of Cape Town during a presentation of new research she and her colleagues have carried out in recent days. Over the past week, it has become increasingly clear that Omicron can deftly evade antibodies, part of the body’s first line of defense, which likely explains why infections with the variant have exploded in many countries. Infections are happening more frequently in two groups of people who carry antibodies: those who have received shots, as well as those who aren’t vaccinated but had recovered from an earlier infection with the coronavirus. At Wednesday’s meeting, one scientist after another presented laboratory findings showing that antibodies are performing more poorly against Omicron than against other variants. But the researchers also presented data showing that boosters of mRNA vaccines — Pfizer-BioNTech and Moderna — can restore antibodies to levels believed high enough to provide strong protection against Omicron infection. Epidemiological findings from Britain and South Africa also suggest that boosters reduce the risk. Speaking at the White House on Wednesday, Dr. Anthony S. Fauci, the administration’s lead adviser on the pandemic, echoed those findings. “Our booster vaccine regimens work against Omicron,” he said. Many countries are rushing boosters to their populations, but Omicron is spreading so fast it may well outstrip even the best efforts. “The projected transmission rates, if borne out, do not give us much time for interventions,” Phil Krause, a former vaccine regulator at the Food and Drug Administration, said at the W.H.O. meeting. That prospect has led many scientists to hope that T cells will serve as an effective backup when antibodies fail. If these immune cells can fight Omicron, they may prevent many infections from turning into severe disease. After a cell is infected with the coronavirus, T cells can learn to recognize fragments of viral proteins that end up on the cell’s outer surface. The T cells then kill the infected cell, or alert the immune system to launch a stronger attack against the virus. Alessandro Sette, an immunologist at the La Jolla Institute for Immunology, and Andrew Redd of the National Institutes of Health reported that despite Omicron’s many mutations, most of the protein fragments recognized by T cells are identical to those of other variants. Those findings suggest that T cells trained by vaccines or previous infections will respond aggressively to Omicron, rather than standing by. “It appears the T cell response is largely preserved,” Dr. Sette said. Dr. Burgers and her colleagues tested that possibility by collecting T cells from 16 people vaccinated with two doses of the Pfizer-BioNTech vaccine and exposing those T cells to protein fragments from the Omicron variant. The scientists found that the response of the T cells to the variant was about 70 percent as powerful as their attack on the original form of the virus. Some scientists cautioned that these data come from studying cells in a laboratory, known as in vitro experiments. It will take a few more weeks of examining real infections in people before anyone knows for sure how well T cells prevent severe disease. “We don’t know yet what these in vitro findings actually mean for disease severity,” said Nora Gerhards, a virologist at Wageningen University in the Netherlands. “And that’s what it’s all about. Because in the end we want to prevent a collapse of the health care systems in our countries.”