Medical workers move a patient at the intensive care unit (ICU) of the Sotiria hospital, amid the coronavirus disease (COVID-19) pandemic, in Athens, Greece, March 1, 2021.Giorgos Moutafis | ReutersWorld Health Organization officials said Wednesday that scientists are trying to understand why Covid-19 cases are suddenly ticking up across much of the world after weeks of falling numbers.There were 2.6 million new cases reported across the world last week, up 7% from the prior week, WHO said in its weekly epidemiological update that reflects data received as of Sunday morning. That follows six consecutive weeks of declining new cases all over the world.The reversal could be caused by the the emergence of several new, more contagious variants of the coronavirus, relaxing public measures and so-called pandemic fatigue, in which people become tired of following precautions, the WHO said in its weekly report. Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, said during a Q&A event at WHO’s headquarters in Geneva on Wednesday that the global health agency is trying to better understand what’s causing the reversal in trends in each region and country.”I can tell you what we’re worried about is with the introduction of vaccines and vaccination in a number of countries, we still need people to carry out their individual-level measures,” she said, urging people to practice physical distancing and continue to wear mask when around others.”By seeing this one week of increase in trends, it’s a pretty stern warning to all of us that we need to stay the course,” Van Kerkhove added. “We need to keep adhering to these measures at hand.”Dr. Mike Ryan, executive director of WHO’s health emergencies program, suggested that the uptick could be because “we may be relaxing a little before we’ve got the full impact of vaccination.” He added that he understands the temptation to socialize more and to revert to more normal behavior, but “the problem is every time we’ve done that before the virus has exploited that.”He reiterated that the cause of the uptick in cases remains unclear, but added that the tried-and-true public health measures that have been emphasized throughout the pandemic are still effective.”When cases are decreasing it’s never everything we do and when they’re increasing it’s never all out fault,” Ryan added.Ryan noted that deaths have not yet risen with cases, but that could change in the coming weeks. Hopefully, he said, a rise in deaths can be avoided due to the vaccination of those most vulnerable to the disease.While the rollout of vaccines is cause for optimism in some countries, Ryan noted that many countries across the world have not yet received doses. He added that 80% of doses have been administered in just 10 countries.The WHO remarks echo those made recently by federal officials in the United States. Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, has been warning for days the decline in daily new cases in the U.S. has stalled out and ticked upward.Over the past seven days, the U.S. reported an average of more than 65,400 daily new cases, according to data compiled by Johns Hopkins University. That’s far below the peak of about 250,000 new cases every day that the country was reporting in early January, but it’s still well above the rate of infection the U.S. saw over the summer when the virus swept across the Sun Belt.”At this level of cases, with variants spreading, we stand to completely lose the hard-earned ground we have gained,” Walensky said Monday. “With these statistics, I am really worried about more states rolling back the exact public health measures we have recommended to protect people from Covid-19.””Please hear me clearly: At this level of cases with variants spreading, we stand to completely lose the hard-earned ground we have gained,” she said.