MEXICO CITY , Mexico -LRB- CNN -RRB- -- Officials in Mexico 's Chiapas state postponed classes Friday for more than 1 million students in an effort to avoid a resurgence of H1N1 flu , which has sickened thousands throughout Mexico this year . After the first confirmed swine flu reports in April , Mexico shut down all of its schools and many public venues . Chiapas Education Secretary Javier Alvarez Ramos and state Health Secretary James Gomez Montes said classes will start August 31 for middle and high school students and September 7 for elementary pupils , the state-run Notimex news agency said . About 1.55 million students will be affected , 850,000 of them in elementary school , Notimex said . This is not the first instance of officials in Mexico altering schedules to combat the disease . The first cases of H1N1 , also called swine flu , were confirmed in Mexico in April . Within days , the government closed all schools and most public venues . In Mexico City , officials shut down all bars , theaters and public gathering places and limited restaurants to take-out orders . About 35,000 businesses were affected . All non-essential federal government offices also were closed nationwide for several days . The World Health Organization declared a global pandemic in early June . As of August 6 , the WHO reported more than 177,450 confirmed cases in 170 nations . The Western Hemisphere has the most cases , with nearly 103,000 confirmed instances of the disease and almost 1,300 deaths . The WHO is no longer providing a country-by-country breakdown , but the United States , Argentina and Mexico have had the most cases and fatalities . In the United States , federal officials released new guidelines this month for containing the spread of the virus across the nation 's school system . Government officials have warned of a possible resurgence in the H1N1 virus this fall . Among other things , health officials urged local administrators to exercise caution and restraint when deciding whether to close a school in response to an outbreak , noting that the costs of shutting down institutions often outweigh the benefits . Officials also confirmed that a new vaccine to combat the virus is likely to be ready by October . The revised federal guidelines advise parents to keep children infected with the H1N1 virus out of school for 24 hours after the fever has gone away . Parents were previously advised to keep their children out of school for seven days after the end of a fever caused by H1N1 . The virus has spread around the world with unprecedented speed , according to the WHO . Past influenza viruses have needed more than six months to spread as widely as the current H1N1 virus spread in less than six weeks , the WHO said .