( CNN ) -- The Centers for Disease Control and Prevention received a candidate vaccine virus for swine flu from one institution Friday , spokesman Thomas Skinner said in an e-mail . The CDC estimates more than 100,000 people have had swine flu in the United States . The CDC and the U.S. Food and Drug Administration have also created a candidate vaccine virus for swine flu , also known as 2009 H1N1 , using reverse genetics , he said . `` Suitable viruses will hopefully be sent to manufacturers by end of next week , '' Skinner wrote . Once that happens , vaccine makers will tweak the virus and have `` pilot lots '' of vaccine ready to be tested by mid- to late June . Several thousand cases have been reported nationally , but the CDC estimates more than 100,000 people have had swine flu in the United States , said Dr. Anne Schuchat , interim deputy director for science and public health program at the CDC , in a news conference Friday . Most of these people probably have not been officially tested . The first sample virus came from a lab run by virologist Doris Bucher at New York Medical College , in Valhalla , New York . Bucher told CNN Thursday that she had just packaged four viruses that she considers vaccine candidates and sent the samples to the CDC 's headquarters in Atlanta , Georgia , via courier . Earlier this week , a Korean scientist , Dr. Seo Sang-heui , also claimed to have produced a virus that might be used in a swine flu vaccine . But Skinner said the methods Sang-heui used were not suitable and that his virus was not considered a viable candidate . Bucher 's samples will likely get more attention . For the past five years her lab in Valhalla has produced elements of the seasonal vaccine that 's given to tens of millions of Americans each year . She says the process she 's using with the H1N1 virus is virtually identical to the process her lab uses when working on that seasonal vaccine . The virus used in vaccines is not the actual virus that infects people , but rather a hybrid that 's been genetically modified to make it safer , and to give it the ability to multiply more quickly -- a crucial factor when it comes to manufacturing large quantities . Bucher 's method of achieving this has a decidedly old-fashioned feel . She first injects a sample of `` wild virus '' -- in this case , H1N1 virus she got from the CDC , originally culled from a child who was infected in California this spring -- and then injects a sample of another flu strain that 's known for its ability to rapidly multiply in eggs . For that , Bucher is using a strain with the exotic sounding name of NYMC X-157 . ( That 's NYMC as in `` New York Medical Center ; '' it 's a hybrid of an H3N2 seasonal virus and the so-called `` Puerto Rico strain , '' A/PR/8/34 , that 's used to speed the growth of seasonal flu vaccine ) . Together in the egg , the viruses swap genes . In a laborious series of steps , Bucher 's team guides the changes by adding antibodies that eliminate the surface proteins of the H3N2 virus . The end result is a virus with the exterior proteins of the H1N1 swine flu -- so the immune system recognizes it -- but with the inner mechanics -- the fast-growth ability -- of X-157 . Another method of creating a candidate virus also mixes wild virus with a second , fast-growing strain , but instead of growing them in eggs , lets the viruses mingle in a special solution while scientists manipulate them through a complex technique called reverse genetics . In 2005 , Dr. Richard Webby and Dr. Robert Webster at St. Jude Hospital in Memphis , Tennessee , used reverse genetics to produce a vaccine against the H5N1 avian flu virus . Webby has been working to produce a candidate virus against H1N1 as well , but told CNN the virus is growing slower than expected , and that it would likely be a few weeks before a suitable strain is ready to be sent to the CDC . With any candidate strain , CDC virologists will perform tests to see if the new virus can induce an immune response against the wild H1N1 strain . That 's done by using a solution derived from the blood of ferrets , whose susceptibility to flu is similar to that of humans , and also by deliberately trying to infect live ferrets . If test results are acceptable , the CDC will forward samples of the virus to various manufacturers . Those companies will fine-tune the virus for their own production methods , and produce small `` pilot lots '' of vaccine that can be tested in animals , and possibly people , for effectiveness and safety . Only after those tests are complete would the CDC , World Health Organization and other government health authorities decide whether to recommend mass production . Even in the fastest-moving scenarios , that step is n't likely to occur before late June or even July . CNN 's Elizabeth Landau contributed to this report .
The CDC received a candidate vaccine virus for testing on Friday . CDC : Suitable vaccine will hopefully be sent to manufacturers by end of next week . In one vaccine method , viruses swap genes in egg . Another method uses reverse genetics instead of growing viruses in egg .