MEXICO CITY, Jan 6 (Reuters) - Mexico is likely to surpass 300,000 deaths from COVID-19 this week - the fifth highest death toll worldwide - as infections rise after the holiday season, fueled by the Omicron coronavirus variant and largely unrestricted tourism. Infections have more than doubled to 20,000 during the last week when many tourists visited Mexico from the United States and Canada. Eleven of Mexico"s 32 states decided not to resume in-person school classes this week with cases climbing fast. The arrival of the highly contagious Omicron variant reversed a downturn in infections during the autumn, when the widespread application of vaccines provided relief. Some Mexicans said people had dropped their guard as the holidays came. "Since December, a lot of people started to go out and there are many who no longer wear face masks," said Isauro Perez, a 53-year-old taxi driver in Mexico City. "If we don"t take care of ourselves, the government won"t take care of us." As of Wednesday, Mexico had registered 299,805 confirmed deaths from COVID-19, a figure that is likely significantly below the real toll, officials say. Separate government data showed there had been nearly 452,000 deaths "linked to" COVID-19 by mid-December, and lower testing has likely helped to understate the reach of the virus. Mexico has the highest fatality rate - deaths per confirmed cases - among the 20 nations most affected by COVID-19 worldwide, according to an analysis by Johns Hopkins University. Laurie Ximenez-Fyvie, an expert on molecular genetics at the National Autonomous University of Mexico (UNAM), said in the end, Mexico"s death toll would be the ultimate yardstick of how the government had performed in the pandemic. So far, she argued, it risked suffering "absolute failure." According to figures from Our World in Data, a research group at Oxford University, in the week ending Jan. 1, Mexico was conducting just 0.12 coronavirus daily tests for every 1,000 inhabitants - down from a peak of 0.38 per day in mid-August. Britain, by contrast, was doing 20.6 tests a day per 1,000 inhabitants as 2021 ended. While parts of Europe and the United States have imposed added restrictions with the spread of Omicron, Mexico has so far resisted and tourists do not require negative tests to enter the country. Videos of maskless travelers drinking alcohol and gathering close together while taking a charter flight to the Mexican beach destination of Cancun from Montreal in late December went viral, prompting Canadian Prime Minister Justin Trudeau to call for an investigation. "It"s a slap in the face," he said. The surge of new cases could hit Mexico harder than some countries since it has a lower vaccination rate than the United States and much of Europe, health experts said. Nationwide, only 56% of the population is fully vaccinated, in comparison to 62% in the United States and 81% in Spain. But Mexicans have readily taken up vaccines, and 95% of adult residents of Mexico City are fully vaccinated. However, the government has not rolled out its vaccination program to people below the age of 15, despite more children being hospitalized. More than one in four of Mexico"s population are aged 14 or below, World Bank data show.