In the lab, immune cells put up a strong fight against Omicron, suggesting that vaccines will be able to prevent the worst outcomes of the virus variant.A flurry of new laboratory studies indicate that vaccines, and especially booster shots, may offer protection against the worst outcomes from the fast-spreading Omicron coronavirus variant. The highly mutated virus, however, will still cause many breakthrough infections in vaccinated people and in those who have been infected with older versions of the virus, according to the research.At a World Health Organization meeting on Wednesday, scientists reported on several studies suggesting that T cells in vaccinated people can put up a strong defense against the variant, which could help prevent severe disease, hospitalization and death.Also on Wednesday, Dr. Anthony S. Fauci, President Biden’s top medical adviser for the coronavirus response, shared preliminary data from his institute’s analysis of the Moderna vaccine. While two shots produced a negligible antibody response against Omicron in the laboratory, the protection shot up after a third dose, he said.Other researchers at the W.H.O. meeting presented similar results, showing that booster shots of either Moderna or Pfizer-BioNTech mRNA vaccines lifted antibodies back to levels believed high enough to offer strong protection against infection.Though the research is based on preliminary observations of cells in the laboratory, it is nevertheless a welcome departure from a torrent of worrying new data about Omicron. 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 probably explains why infections with the variant have exploded in many countries. But antibodies are not the only important players in a person’s immune response to the virus. T cells have their own role.“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.Dr. Anthony Fauci spoke at the White House this month about the new variant. “Our booster vaccine regimens work against Omicron,” he said on Wednesday.Doug Mills/The New York TimesOmicron 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 have recovered from an earlier infection with the coronavirus.This week, scientists in South Africa reported that two doses of the Pfizer vaccine were 33 percent effective against an Omicron infection, down from about 80 percent during what Dr. Fauci called “the pre-Omicron era.” The study found that two doses of the Pfizer vaccine offered 70 percent protection against severe hospitalization and death, down from about 95 percent before Omicron was detected.At Wednesday’s W.H.O. meeting, one scientist after another presented similar laboratory findings showing that vaccine-induced antibodies performed much worse against Omicron than against other variants.But boosters seem to provide enough extra antibodies to lessen these infections. Dr. Fauci described experiments at the National Institutes of Health, in which scientists took blood serum from people who had two doses of the Moderna vaccine as well as from others who had a third dose. The researchers then mixed the serum with viruses engineered to carry Omicron’s surface proteins.These “pseudoviruses” evaded many antibodies from people who had received two doses of Moderna, but the boosters produced such high levels of antibodies that the viruses were blocked from invading cells.“So the message remains clear: If you are unvaccinated get vaccinated, and particularly in the arena of Omicron, if you are fully vaccinated, get your booster shot,” Dr. Fauci said.Dr. Fauci’s admonition comes as Biden administration officials are bracing for a potential wave of Omicron infections that could overwhelm the health care system. The Centers for Disease Control and Protection warned recently that the percentage of coronavirus cases in the United States caused by the Omicron variant had increased sharply and might portend a significant surge in infections as soon as next month. The Delta variant remains by far the dominant version across the United States.In anticipation of that wave, the administration is trying to encourage all Americans who are eligible — those 16 and older who received their second vaccine dose at least six months ago — to get their booster shots. About 27 percent of fully vaccinated Americans have also had booster shots, according to the C.D.C.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.A line for Covid boosters at St. Thomas’ Hospital in London. Many countries are rushing booster shots to their populations, but Omicron may be spreading too quickly for them to keep up.Dan Kitwood/Getty ImagesThat 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.The Coronavirus Pandemic: Key Things to KnowCard 1 of 4U.S. surpasses 800,000 deaths.

In the lab, immune cells put up a strong fight against Omicron, suggesting that vaccines will be able to prevent the worst outcomes of the virus variant.A flurry of new laboratory studies indicate that vaccines, and especially booster shots, may offer protection against the worst outcomes from the fast-spreading Omicron coronavirus variant. The highly mutated virus, however, will still cause many breakthrough infections in vaccinated people and in those who have been infected with older versions of the virus, according to the research.At a World Health Organization meeting on Wednesday, scientists reported on several studies suggesting that T cells in vaccinated people can put up a strong defense against the variant, which could help prevent severe disease, hospitalization and death.Also on Wednesday, Dr. Anthony S. Fauci, President Biden’s top medical adviser for the coronavirus response, shared preliminary data from his institute’s analysis of the Moderna vaccine. While two shots produced a negligible antibody response against Omicron in the laboratory, the protection shot up after a third dose, he said.Other researchers at the W.H.O. meeting presented similar results, showing that booster shots of either Moderna or Pfizer-BioNTech mRNA vaccines lifted antibodies back to levels believed high enough to offer strong protection against infection.Though the research is based on preliminary observations of cells in the laboratory, it is nevertheless a welcome departure from a torrent of worrying new data about Omicron. 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 probably explains why infections with the variant have exploded in many countries. But antibodies are not the only important players in a person’s immune response to the virus. T cells have their own role.“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.Dr. Anthony Fauci spoke at the White House this month about the new variant. “Our booster vaccine regimens work against Omicron,” he said on Wednesday.Doug Mills/The New York TimesOmicron 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 have recovered from an earlier infection with the coronavirus.This week, scientists in South Africa reported that two doses of the Pfizer vaccine were 33 percent effective against an Omicron infection, down from about 80 percent during what Dr. Fauci called “the pre-Omicron era.” The study found that two doses of the Pfizer vaccine offered 70 percent protection against severe hospitalization and death, down from about 95 percent before Omicron was detected.At Wednesday’s W.H.O. meeting, one scientist after another presented similar laboratory findings showing that vaccine-induced antibodies performed much worse against Omicron than against other variants.But boosters seem to provide enough extra antibodies to lessen these infections. Dr. Fauci described experiments at the National Institutes of Health, in which scientists took blood serum from people who had two doses of the Moderna vaccine as well as from others who had a third dose. The researchers then mixed the serum with viruses engineered to carry Omicron’s surface proteins.These “pseudoviruses” evaded many antibodies from people who had received two doses of Moderna, but the boosters produced such high levels of antibodies that the viruses were blocked from invading cells.“So the message remains clear: If you are unvaccinated get vaccinated, and particularly in the arena of Omicron, if you are fully vaccinated, get your booster shot,” Dr. Fauci said.Dr. Fauci’s admonition comes as Biden administration officials are bracing for a potential wave of Omicron infections that could overwhelm the health care system. The Centers for Disease Control and Protection warned recently that the percentage of coronavirus cases in the United States caused by the Omicron variant had increased sharply and might portend a significant surge in infections as soon as next month. The Delta variant remains by far the dominant version across the United States.In anticipation of that wave, the administration is trying to encourage all Americans who may be eligible — those 16 and older who received their second vaccine dose at least six months ago — to get their booster shots. About 27 percent of fully vaccinated Americans have also had booster shots, according to the C.D.C.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.A line for Covid boosters at St. Thomas’ Hospital in London. Many countries are rushing booster shots to their populations, but Omicron may be spreading too quickly for them to keep up.Dan Kitwood/Getty ImagesThat 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.The Coronavirus Pandemic: Key Things to KnowCard 1 of 4U.S. surpasses 800,000 deaths.