▁from ▁currently ▁circul ating ▁human ▁influen za ▁H 1 ▁and ▁H 3 ▁vir uses . ▁These ▁vir uses ▁include ▁those ▁that ▁are ▁sub ty ped ▁as ▁non human ▁in ▁origin ▁and ▁those ▁that ▁are ▁un sub typ able ▁with ▁standard ▁methods ▁and ▁re ag ents . ▁The ▁new ▁stra in ▁responsible ▁for ▁this ▁out break ▁was ▁one ▁such ▁virus . ▁ ▁Re comm end ations ▁for ▁schools ▁Initial ly ▁the ▁CD C ▁had ▁issued ▁a ▁recommendation ▁that ▁schools ▁close ▁for ▁as ▁long ▁as ▁two ▁weeks ▁if ▁a ▁student ▁catch es ▁sw ine ▁flu . ▁Some ▁school ▁districts ▁closed ▁all ▁schools ▁if ▁a ▁single ▁child ▁was ▁class ified ▁as ▁probable . ▁On ▁May ▁ 5 ▁the ▁CD C ▁ret ract ed ▁its ▁advice ▁stating ▁that ▁schools ▁that ▁were ▁closed ▁based ▁on ▁previous ▁CD C ▁guidance ▁related ▁to ▁this ▁out break ▁may ▁re open . ▁By ▁that ▁time ▁at ▁least ▁ 7 2 6 ▁schools ▁nation wide ▁serving ▁more ▁than ▁ 4 8 0 , 0 0 0 ▁students ▁had ▁closed ▁for ▁at ▁least ▁some ▁period ▁of ▁time . ▁The ▁CD C ▁am ended ▁its ▁advice , ▁cit ing ▁new ▁information ▁on ▁disease ▁sever ity ▁and ▁the ▁limit ing ▁effect iveness ▁of ▁school ▁closure ▁as ▁a ▁control ▁measure . ▁The ▁new ▁advice ▁given ▁stated , ▁" Dec isions ▁about ▁school ▁closure ▁should ▁be ▁at ▁the ▁dis cret ion ▁of ▁local ▁authorities ▁based ▁on ▁local ▁consider ations , ▁including ▁public ▁concern ▁and ▁the ▁impact ▁of ▁school ▁abs ente e ism ▁and ▁staff ing ▁short ages ."