2 5 , ▁ 2 0 0 9 , ▁ 4 2 ▁schools ▁were ▁closed ▁in ▁eight ▁states ▁as ▁the ▁second ▁wave ▁of ▁the ▁pan demic ▁began . ▁ ▁On ▁May ▁ 5 , ▁Kath le en ▁Seb el ius ▁stated ▁in ▁a ▁CD C ▁news ▁conference ▁that ▁school ▁clos ures ▁for ▁single ▁confirmed ▁cases ▁of ▁H 1 N 1 ▁influen za ▁were ▁unnecessary , ▁but ▁that ▁parents ▁keep ▁their ▁child ▁home ▁if ▁he ▁or ▁she ▁displays ▁an ▁influen za - like ▁ill ness . ▁ ▁Tra vel ▁industry ▁Several ▁US ▁air lines ▁wa ived ▁fe es ▁for ▁can cell ations ▁and ▁flight ▁changes . ▁At ▁least ▁one ▁cru ise ▁line ▁changed ▁it iner ary ▁to ▁avoid ▁Mexican ▁ports ▁of ▁call . ▁ ▁Sum mary ▁ ▁See ▁also ▁▁▁ 2 0 2 0 ▁coron av irus ▁pan demic ▁in ▁the ▁United ▁States ▁ ▁Spanish ▁flu ▁ ▁References ▁ ▁External ▁links ▁ ▁U . S . ▁federal ▁government ▁Pan demic F lu . gov ▁– ▁Access ▁to ▁U . S . ▁Government ▁sw ine , ▁av ian ▁and ▁pan demic ▁flu ▁information . ▁U . S . ▁Cent ers ▁For ▁D ise ase ▁Control ▁( CD C ) ▁H 1 N 1 ▁Fl u ▁– ▁Up dates ▁period ically ▁as ▁the ▁CD C ▁releases ▁new ▁information ▁Medical ▁Encyclopedia ▁Med line ▁Plus : ▁Sw ine ▁Fl u ▁Encyclop ic ▁Information ▁from ▁the ▁National ▁Instit utes ▁of ▁Health ▁ ▁International ▁organizations ▁ ▁World ▁Health ▁Organ ization ▁( W HO ) ▁In fl uen za ▁A (