Dec 16 (Reuters) - Americans face an uncertain and anxiety-filled holiday season for the second consecutive year, as the highly contagious Omicron variant threatens to intensify an already alarming surge of COVID-19 cases. Public health officials have voiced deepening concerns about the rising number of infections, warning that hospitals - still fighting the effects of the Delta variant - could find themselves stretched beyond their limits if the two variants combine to create a fresh wave. While states have not sought to impose broad shutdowns, the disease"s advances have prompted a new round of restrictions, as offices have postponed return-to-office dates, universities have moved exams online and some states and cities have reimposed mask mandates. In New York City, several Broadway shows, including "Hamilton," "Tina" and "Mrs. Doubtfire: The Musical" canceled performances, citing breakthrough COVID infections among their cast or crew. In Puerto Rico, the finale of the Miss World beauty pageant was called off on Thursday after several contestants tested positive. Dr. Anthony Fauci, the top U.S. infectious disease expert, said on Thursday that the Omicron variant would soon dominate infections. "We"ve seen that in South Africa, we"re seeing it in the UK, and I"m absolutely certain that"s what we"re going to be seeing here relatively soon," said Fauci, who met with President Joe Biden on Thursday afternoon to discuss the government"s response. In South Africa, the United Kingdom and Denmark, the number of new Omicron infections has been doubling every two days. Preliminary data suggests Omicron may be more contagious than Delta but less likely to cause severe illness, though much remains unknown. Research also indicates that the two-dose vaccine regimens have vastly reduced protection against Omicron but that a third booster dose restores much of the vaccine"s efficacy. Experts have warned that Omicron could still have deadly consequences due to its transmissibility. "When you have a disease that is highly infectious – even if it causes milder disease – you can still have many, many deaths, Dr. Celine Gounder, an infectious disease expert, said during a panel discussion at New York University on Thursday. Maine set a record for the number of hospitalized COVID patients on Wednesday, a day after Michigan hit a new high. New Jersey recorded its highest number of cases on Thursday since mid-January, at the peak of last winter"s surge. Over the past month, new cases have risen nearly 40% to a seven-day average of 121,000 new infections per day, according to a Reuters tally. Deaths have risen 18% since mid-November to an average of 1,300 lives lost a day. COVID hospitalizations have risen about 45% over the last month. In New York City, the percentage of people testing positive for COVID-19 doubled in three days, according to Dr. Jay Varma, a senior public health adviser to Mayor Bill de Blasio. "We"ve never seen this before in #NYC," he wrote on Twitter, adding that the only explanation is Omicron"s ability to evade both natural and vaccine-induced immunity. De Blasio announced the city would ramp up capacity at testing sites, which have seen long lines in recent days, and distribute 500,000 rapid at-home test kits through community organizations. "This variant moves fast," he said. "We need to move faster." New York Governor Kathy Hochul said the state would allow residents to request test kits be mailed to their homes, joining several other U.S. states. U.S. President Joe Biden said on Thursday it is past time for people to get booster shots and urged them to do so as quickly as possible. “We are looking at a winter of severe illness and death” for the unvaccinated, Biden said. HOLIDAY TRAVEL CONCERNS The surge has prompted worried Americans to reconsider holiday travel plans. Experts have said vaccinated individuals can travel safely as long as they wear masks and avoid unnecessary risks such as large crowds and indoor gatherings. After months of planning a trip to Florida to see his parents for Christmas and his mother"s birthday, Kalaya"an Mendoza of Queens, New York, told Reuters he was forced to cancel when he learned that several people at an event he attended on Monday had tested positive. "I"m a little bit wrecked," Mendoza, 43, said on Thursday. "It feels like 2020 all over again. I had to weigh my very intense Filipino need to be with family with their care and safety." Mendoza, who has not seen his parents since December 2019, said he was angry at how little progress the U.S. government had made on fighting the pandemic while spending billions of dollars this year on other items, such as the military. "I remember watching my neighbors get carted away in body bags at the start of this pandemic, and two years in, we shouldn"t be here," he said.