Story highlights Josh Hardy has received three doses of an experimental drug

His mother says she is "beside myself with how effective this drug was"

A drug company initially refused to provide the medication

The company relented after reports by CNN and pressure from social media

After just three doses of an experimental drug, Josh Hardy -- whose parents had to launch a media campaign to get him the medicine -- is sitting up, doing homework and playing board games with his brothers, his mother said.

Just last week, Josh was so sick he could barely get out even a few words. He was in heart and kidney failure, and vomited blood several times an hour as his family held a vigil in the intensive care unit of a Memphis hospital.

Josh received doses of the drug brincidofovir Wednesday, Saturday, and Tuesday, and tests showed the level of adenovirus in his blood went down from 250,000 copies per milliliter to 367 copies per milliliter.

"We expect it will be out of his system by Tuesday," his mother, Aimee Hardy, said Friday. "I'm beside myself with how effective this drug was so quickly."

Already they're seeing results of the waning virus in Josh's system. He no longer has bleeding in his stomach and intestines.

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Before receiving brincidofovir, Josh was fighting for his life. The adenovirus was ravaging his immune system, left vulnerable by treatment for cancer, and the only available antiviral drug to treat it wasn't working.

In early February, Chimerix, the company that makes brincidofovir, refused to give Josh its experimental drug . But after reports by CNN and intense pressure from social media, Chimerix and the Food and Drug Administration came up with a plan to get the medicine to Josh and other patients who request it.

Traditionally, drug companies have not been allowed to use so-called "compassionate use" patients like Josh as study subjects, so helping them out has been pure charity work on behalf of the drug company.

But the FDA allowed Chimerix to use data from Josh and others as part of its application to the FDA, helping to get the drug on the market faster.

Josh Hardy has beaten cancer four times.

Seven other adenovirus patients have inquired about being the next in line to get the drug, according to Kenneth Moch, the president of Chimerix, and several of those patients have already received doses.

Even though the virus seems to be leaving Josh's body, his mother says his kidneys are still in danger.

In February, his kidneys were just starting to recover from the damage of powerful chemotherapy. But then the adenovirus struck, and his doctors had no choice but to give him an antiviral drug that further damaged his kidneys.

Now that Josh is taking brincidofovir, he's no longer taking the other drug that hurt his kidneys, but the damage was done: His kidneys still aren't working and he has to undergo dialysis three times a week. His mother worries he might be on dialysis the rest of his life.

"What if he has to be on dialysis long-term? If he could have gotten the brincidofovir earlier, it could have been avoided. That will always bother me," she said.

Josh Hardy was in critical condition last week.

She's also worried about something else -- Josh's state of mind.

As recently as last month, Josh had a "go get 'em" attitude about fighting his illness, his mother says. But now, even though he's getting better, she says he seems to be exhausted after months of being sick and lacks motivation.

"I haven't seen him smile lately," she said. "I try to get him to chant every day, 'I'm as good as new.' "