The Porygon Epidemic

"Dennō Senshi Porygon" (Japanese: でんのうせんしポリゴン, Hepburn: Dennō Senshi Porigon, translated as "Computer Warrior Porygon", although more commonly "Electric Soldier Porygon") is the 38th episode of the Pokémon anime's first season. Its sole broadcast was in Japan on December 16, 1997. In the episode, Ash and his friends find at the local Pokémon Center that there is something wrong with the Poké Ball transmitting device. To find out what is wrong, they must go inside the machine.

The episode contained repetitive visual effects that induced photosensitive epileptic seizures in a substantial number of Japanese viewers, an incident referred to as the "Pokémon Shock" (ポケモンショック, Pokemon Shokku) by the Japanese press. 685 children across Japan were taken to hospitals; two remained hospitalized for more than two weeks. The shares of Nintendo, the company that produced the games they were based on, fell by about 3.2%. As a result of this incident, Nintendo ordered the episode pulled from rotation and it has not aired in any country since.

After the incident, the Pokémon anime went into a four-month hiatus, removing the TV Tokyo red circle "チュッ!" logo from the Japanese anime, and it returned on TV Tokyo on April 16, 1998. After that, the time slot changed from Tuesday to Thursday. Since then, the episode has been parodied and referenced in cultural media, including The Simpsons episode "Thirty Minutes over Tokyo" and the South Park episode "Chinpokomon".

Plot
Ash, Misty, Brock and Pikachu make their way to the nearest Pokémon Center, where they discover that the Poké Ball transmitting device is malfunctioning. On Nurse Joy's request, they go to Professor Akihabara, the one who created the Poké Ball transfer system. He tells them that Team Rocket stole his prototype Porygon, a digital Pokémon that can exist in cyberspace, and is using it to steal trainers' Pokémon from inside the computer system.

Akihabara sends Ash, Misty, Brock, Pikachu and his second Porygon into the cyberspace system, using his Dimension Transporter, to stop Team Rocket, whom they learn have set up a blockade that stops Pokéballs from traveling the network. Porygon is able to defeat Team Rocket's Porygon; unfortunately, Nurse Joy, monitoring the situation and unaware that Ash and the others are inside, has sent an antivirus program into the system to combat the computer virus Team Rocket set up. In the ensuing chaos, Pikachu uses a Thunderbolt attack on the program, which manifests as 4 cyber missiles, which causes a large explosion. Two of the missiles enter the portal, completely destroying Akihabara's house, much to his dismay, as his Dimension Transporter is now broken. The group and Team Rocket successfully escape the computer, and with Team Rocket's blockade removed, the Poké Ball transmitting device returns to normal.

Broadcast
"Dennō Senshi Porygon" had its sole broadcast in Japan on Tuesday, December 16, 1997, at 6:30 PM Japan Standard Time (09:30 UTC). It was broadcast over 37 TV stations that Tuesday night. It held the highest ratings for its time slot, and was watched by approximately 4.6 million households.

Strobe lights
Twenty minutes into the episode, Pikachu stops "vaccine" missiles with his Thunderbolt attack, resulting in an explosion that flashes red and blue lights. Although there were similar parts in the episode with red and blue flashes, two anime techniques, called "paka paka" and "flash", made the scene particularly intense. These flashes were bright strobe lights, with blinks at a rate of about 12 Hz for approximately six seconds.

At this point, some of the viewers experienced blurred vision, headaches, dizziness and nausea. Some suffered seizures, blindness, convulsions and loss of consciousness. Japan's Fire Defense Agency reported that 685 viewers – 310 boys and 375 girls – were taken to hospitals by ambulances. Although many victims recovered during the ambulance trip, more than 150 were admitted to hospitals. Two were hospitalized for more than two weeks. Some had seizures when parts of the scene were rebroadcast during news reports on the seizures. The incident was referred to as "Pokémon Shock" (ポケモンショック, Pokémon Shokku) by the Japanese press.

Later studies showed that 5–10% of the viewers had mild symptoms that did not need hospital treatment. Twelve thousand children who were not sent to hospital reported mild symptoms of illness; however, their symptoms more closely resembled mass hysteria than a seizure. A study following 103 patients over three years after the event found that most had no further seizures. Although approximately 1 in 4,000 people are susceptible to these types of seizures, the number of people affected by the Pokémon episode was unprecedented.

An article in USA Today reassured parents that American children were unlikely to suffer seizures provoked by cartoons as U.S. networks at the time rarely aired anime, with its "fast-paced style of animation", though in early January following the incident 4Kids Entertainment announced that they intended to air Pokémon in the U.S., albeit with the seizure-inducing effects removed. It has been suggested that without the publicity around the seizures, Pokémon would most likely never have been localized to the U.S. Pokémon successfully premiered in the U.S. (without this episode) over a year after the incident, with more children's anime airing on broadcast and cable networks in the U.S. immediately afterwards. The incident was included in the 2004 edition and the 2008 Gamer's Edition of the Guinness World Records book, holding the record for "Most Photosensitive Epileptic Seizures Caused by a Television Show".

Aftermath
News of the incident spread quickly through Japan as well as the headquarters of Nintendo, the company that develops the games the anime was based on. The following day the television station that had originated the lone broadcast of that episode, TV Tokyo, issued an apology to the Japanese public, suspended the program, and said it would investigate the cause of the seizures. Officers from Atago Police stations were ordered by Japan's National Police Agency to question the anime's producers about the show's contents and production process. An emergency meeting was held by the Ministry of Health, Labour and Welfare, in which the case was discussed with experts and information collected from hospitals. Video retailers all over Japan removed the Pokémon anime from their rental shelves.

Reaction was swift on the Tokyo Stock Exchange, and Nintendo's shares fell by 400 yen (almost 3.2%) the following morning to 12,200 yen. The president of Nintendo, Hiroshi Yamauchi, said at a press conference the day after the episode had aired that the video game company was not responsible since the original Pokémon game for its Game Boy product was presented in black and white.

After the airing of "Dennō Senshi Porygon", the Pokémon anime went into a four-month hiatus. Its time slot was taken over by Class King Yamazaki (学級王ヤマザキ). All 37 episodes of Pokémon: Indigo League were rerun on Kids Station in Tokyo before the show returned on April 16, 1998, with airing of "Forest of Pikachu" ("Pikachu's Goodbye") and "The Four Eevee Brothers" ("The Battling Eevee Brothers"). After the hiatus, the time slot changed from Tuesday to Thursday. Several episodes (including the opening, credits, and "Dare da?" segments) were heavily edited to reduce flashing lights (with special emphasis on lightning that consumes the screen.) Before the resumption of broadcast, "Problem Inspection Report on the Pocket Monsters Anime" (アニメ ポケットモンスター問題検証報告, Anime Poketto Monsutā Mondai Kenshō Hōkoku) was shown. Broadcast in Japan on April 16, 1998, host Miyuki Yadama went over the circumstances of the program format and the on-screen advisories at the beginning of animated programs, as well as showing letters and fan drawings sent in by viewers, most of whom were concerned that the incident would lead to the anime being cancelled. Many Japanese television broadcasters and medical officials (along with the United Kingdom’s Independent Television Commission) came together to find ways to make sure the incident was not repeated. They established a series of guidelines for future animated programs, including:
 * Flashing images, especially those with red, should not flicker faster than three times per second. If the image does not have red, it still should not flicker faster than five times per second.
 * Flashing images should not be displayed for a total duration of more than two seconds.
 * Stripes, whirls and concentric circles should not take up a large part of the television screen.

This episode kept the episodes "Rougela's Christmas" ("Holiday Hi-Jynx") and "Iwark as a Bivouac" ("Snow Way Out!") off their original broadcast date in Japan following the incident. Those two episodes were about to air after "Dennō Senshi Porygon" on December 23, 1997, and January 6, 1998, respectively. They were eventually only aired on October 5, 1998, as an hour-long special. Airing out of order caused confusion to viewers because Ash still had a Charmander instead of Charizard, and Misty did not have Togepi yet, but Starmie and Horsea. Also, a New Year special was about to air between these episodes on December 30, 1997, but it was cancelled after TV Tokyo pulled any mention of Pokémon from their channel following the incident.

To prevent any similar incidents from occurring, Yamauchi quickly ordered the episode pulled from circulation, and it has not aired since in any country. After the Pokémon incident, TV broadcasters voluntarily added on-screen warnings to shows targeted at young children encouraging viewers to watch anime in a well-lit room and to sit far away from the television set. The anime has not featured Porygon or its evolutions, Porygon-2 and Porygon-Z, in any subsequent episodes.

Cultural impact
The "Pokémon Shock" incident has been parodied many times in popular culture, including an episode of The Simpsons, "Thirty Minutes over Tokyo". In the episode, Bart watches an anime entitled Battling Seizure Robots featuring robots with flashing eye lasers, and asks: "Isn't this that cartoon that causes seizures?" The flashing eyes cause him, Marge, Lisa, and Homer to have seizures. The same scene is seen again in the episode's end credits, this time covering the entire screen.

An episode of South Park, "Chinpokomon", revolves around a Pokémon-like phenomenon, called Chinpokomon. Chinpokomon toys and video games are sold to children in South Park by a Japanese company. The company's president, Mr. Hirohito, uses the toys to brainwash the American children, making them into his own army to topple the "evil" American "empire". These toys included a video game in which the player attempts to bomb Pearl Harbor. While playing this game, Kenny has an epileptic seizure and later dies.

In the pilot episode of Drawn Together, Ling-Ling, who is a parody of Pikachu, states that his goal in the Drawn Together house is to "destroy all, and give children seizures". There follows a scene with flashing lights.

In So Yesterday, a novel by Scott Westerfeld, this episode is mentioned and shown to one of the characters. The flashing red light that caused the seizure is also used in the storytelling elements.

On September 19, 2020, the official Pokémon Twitter account referenced the episode, saying "Porygon did nothing wrong," in reference to the resulting explosion from Pikachu's Thunderbolt attack being the in-universe cause of the flashing lights, not Porygon. The tweet was deleted shortly thereafter, speculated to be because of the taboo subject matter.