(Adds comments from CDC, paragraphs 5-6) By Julie Steenhuysen CHICAGO, April 13 (Reuters) - A U.S. toddler who nearly died from a rare skin reaction to his father's smallpox shot is out of intensive care and on the mend, thanks to a novel combination of drugs that had never been tried in children. "He's making what we hope is a complete recovery," said Dr. John Marcinak, the University of Chicago pediatric infectious disease specialist who has helped treat the child since early March. The 2-year-old Indiana boy, who has been upgraded to fair condition at the University of Chicago's Comer Children's Hospital, developed the rare rash known as eczema vaccinatum after being with his father, a soldier vaccinated for deployment in Iraq. His case has given new insight on the usefulness of drugs to treat smallpox and vaccine-related infections, knowledge that may be of use in the event of a smallpox or other biological attack. "It's very useful information," said Dr. Inger Damon, a pox virus expert at the Atlanta-based U.S. Centers for Disease Control and Prevention. She said the CDC will scrutinize lab tests and other materials gathered throughout the child's treatment to gain a better understanding of what works in such cases. Smallpox was eradicated in 1979 but experts fear some groups might have samples to use as a bioweapon. Smallpox vaccines do not use the smallpox virus, but a closely related and weaker virus called vaccinia. Those who have eczema, like the toddler, are at particular risk for an eczema vaccinatum reaction. The child's case is the first to be reported since smallpox vaccinations resumed in the United States in 2002. For Dennis Hruby, a leading pox virus specialist, the child's recovery is especially gratifying. Hruby, now chief scientific officer of Siga Technologies Inc. <SIGA.O>, did some of the basic research at Oregon State University decades ago that laid the groundwork for Siga's experimental smallpox drug SIGA-246. The drug, which has been proven to work in primates infected with smallpox and monkeypox, was one of several treatments used on the child. Other therapies included an intravenous form of vaccinia immune globulin -- developed in the 1960s to treat complications of smallpox vaccinations. He also received the antiviral drug cidofovir, made by Gilead Sciences Inc. <GILD.O> VERY SICK CHILD "This was a very sick little boy. He was on multiple drug modalities but he was not doing well," Hruby said in a telephone interview. At one point the rash consumed 80 percent of the child's body and he needed skin grafts to protect against infection. Now, Marcinak said, the scabs are nearly all gone. Marcinak and colleagues were having daily calls with a host of health officials, and in one, Dr. Damon suggested the experimental Siga drug. The U.S. Food and Drug Administration granted special permission for its use. "Both his immune response and his viral load improved dramatically," Hruby said. "It wasn't magic, but he started getting better the next day," Dr. Marcinak added. While doctors are still trying to parse out the relative contributions of the different drugs, they know they did little, if any, harm. "He's hasn't really had any significant toxicity related to the medications. He did have a short period of renal failure right after having received the cidofovir, which may have contributed to that," Marcinak said. Renal, or kidney, failure is a known complication of cidofovir, which is used to treat infections in HIV and AIDS patients. "It's exciting to see your drug put to use this way," Hruby said.
