Seth Lane, who is 5 years old, was born with a severe immune system disorder. He was recently filmed by his parents asking people to support him by wearing yellow on March 27.
The little boy from Northamptonshire in England has severe combined immunodeficiency, sometimes called "bubble boy disease," and so has lived in a sterile environment for most of his life.
Before anyone enters his hospital room, even his family, they have to scrub and wear plastic gowns, his mom Leanne wrote on her family's blog. If she has a cold, she can't enter.
Though his first bone marrow transplant was unsuccessful, Seth's dad Nik filmed him smiling and holding up yellow signs asking people to support him for his second by wearing yellow and posting the photos with the hashtag #WearYellowForSeth.
After his first bone marrow transplant, Seth wasn't able to leave his "bubble" or play with other children for two years while he tried to gain back his strength.
"He had no contact with other children until he was two and a half," his mom said.
After finally starting school and getting to make friends last year, Seth's body again became sick in October, and he had to return to his "bubble" — a super-hygienic room at Newcastle's Great North Children's Hospital.
Last week, Nik posted the video on the family's blog, and it's gotten over 2 million views in a few days.
"On 27th March 2015 lots of people are going to wear yellow to show me how much support I have. Are you going to join in?" the cue cards read.
Nik wrote on the blog that they want the pictures to show Seth how many people are thinking of him, and said they'd hang them up around his hospital room.
He wrote, "We have a map of the world in his room and will pin all the countries where people have posted a picture from. Also we will be printing some off and putting them up in his room."
"Whenever he is struggling (which is rare to be fair) we can show him your pictures," he added.
Seth has been in the hospital since January, and after his operation in six weeks, will likely have another year in near-isolation, said Leanne, who also has a 5-month-old son.
"We never meant to start any sort of campaign, and only expected friends and family to join in," Leanne told the Daily Mail. "I can't believe it has taken off like this."
She added, "It all helps show Seth that people are thinking of him. I told him about the views and he asked, "Is it more than 20?' I said, 'yes it is' and he said, 'wowee.'"
BuzzFeed News has reached out to the Lane family for comment.