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Pokérus

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Pokémon infected with Pokérus in Pokémon Adventures

The Pokérus (Japanese: ポケルス Pokérus), from "Pokémon virus", is a microscopic life-form that may attach to Pokémon, first appearing in the Generation II games. It is a beneficial mechanic that a Pokémon can obtain.

In the games

When a Pokémon has the Pokérus, it gains double the effort values from battling (e.g., fighting a Magikarp will give two Speed EVs, rather than one). Effort points gained from vitamins and wings are not doubled. The infected Pokémon can infect other Pokémon with the virus for a period of about two days. However, the Pokérus timer can be delayed by several methods including placing the infected Pokémon in a PC Box.

While it is represented similarly to status conditions, the Pokérus is not a status condition, so it cannot be healed at a Pokémon Center or with any status condition healing item.

Pokérus has a 3 in 65,536 or approximately a 1 in 21,845 chance of being generated on a Pokémon, either wild or bred, effectively making this rarer than a shiny Pokémon, which have a 3 in 24,576, or around 1 in 8,192 chance to be found wild or hatched. Through battling or capturing this wild Pokémon, players could get this helpful virus onto their own Pokémon, and subsequently spread it around. Due to the overwhelmingly low chance of encountering the virus (about 1/3 of the chance to encounter a Shiny Pokémon), and the fact that most would not even recognize a Pokémon with the virus and may flee from it, many players don't have a Pokémon with the virus.

From Generation IV onward, the Pokérus became more accessible, with worldwide trading facilitated by Nintendo Wi-Fi Connection. A Pokémon's chances of being infected with the virus somewhat increase when a Pokémon has been traded from another game.[citation needed]

Infection

050Diglett.png This section is incomplete.
Please feel free to edit this section to add missing information and complete it.
Reason: Generation VI.

When infected, a Pokémon's status screen will indicate it much as it does any other status condition. The icons are different in Generation III, IV and VI, while Generation V has the same as Generation IV and Generation II has no icon at all. When another normal status condition, such as Sleep, affects the Pokémon, the Pokérus icon will be temporarily replaced until the other status condition ends or is cured. As long as the Pokémon is infected with Pokérus, it can spread the virus to the other Pokémon in the player's party. The infection may spread if the infected Pokémon is in the main party after a battle. An uninfected Pokémon must be next to a Pokémon infected with Pokérus in the main party for the virus to spread. If Pokémon that have already been infected and cured from Pokérus are in the main party and are on either side of a Pokémon currently with the disease, Pokérus will not spread to or through them after any amount of battles. For example, if an infected Pokémon is positioned between two cured Pokémon, that particular infected Pokémon is not capable of spreading the Pokérus through the party. However, if an infected Pokémon is positioned between a non-infected Pokémon and a cured Pokémon, Pokérus will only have a chance of spreading through the party on the side of the non-infected Pokémon. Infected Pokémon that are put into the PC will keep the status indefinitely. From Generation III onward, Eggs may catch Pokérus like any other Pokémon.

After having the virus

Once a Pokémon's immune system has fought off the virus, they cannot spread it further, nor can it be spread to them by other Pokémon. In Generations II and III, a dot will appear on the Pokémon's status screen to indicate that they have had the virus previously, while in Generation IV and onward, it will be a small face. Though the virus is gone, its positive effects will remain, most specifically the ability for that Pokémon to gain double EVs.

Any Pokémon on the player's party at the moment the system clock reaches midnight after a certain number of days in that position (number of days depends on the strain and generation) will become immune. An easy way to keep a "vessel" for future spreading is to always send the infected Pokémon to the PC, Day Care, Stadium 2 (in Generation II), Pokémon Box Ruby & Sapphire (in Generation III), My Pokémon Ranch (in Generation IV), or Pokémon Bank (in Generation VI) before midnight. The game also recognizes immunizing if the system is turned off and on again on the next day.

050Diglett.png This section is incomplete.
Please feel free to edit this section to add missing information and complete it.
Reason: What happens when the player performs the "saving inside a Pokémon Center" process described below in other generations besides Generation 3.

In Generation III, if the player deposits an infected Pokémon inside a PC, saves inside a Pokémon Center prior to midnight, shuts off the game, resumes the game after midnight, withdraws the infected Pokémon from the PC, and exits the Pokémon Center, it is possible for the infected Pokémon to be cured of Pokérus upon stepping outside of the building.

Technical information

Pokérus is stored in a Pokémon's data structure as a single byte at offset 0x1C. In hexadecimal, this can be represented as a two-digit number XY. The upper 4 bits of the byte, X, represent the specific strain of Pokérus the Pokémon has contracted. The lower 4 bits, Y, represent the number of days remaining before the infected Pokémon is cured of the virus.

A Pokémon is or has been infected if X (the strain) is a nonzero value. If Y (days remaining) is nonzero when X is also nonzero, this means the Pokémon is currently infected. If Y is 0 and X is nonzero, then the Pokémon is "cured" of Pokérus. If both X and Y are 0, then the Pokémon has never been affected by Pokérus.

Whenever the game's internal clock strikes midnight, every currently infected Pokémon in the player's party has their Pokérus value decreased by one. Once the Y value reaches 0, the Pokémon will be cured of Pokérus.

Strains

Whenever the game creates Pokérus on a Pokémon, the value assigned to Y (days) depends on the value assigned to X (strain). Specifically, the number of days will be set to X modulo 4 + 1. In other words, the higher two bits of X are irrelevant to the "strain".

Strain X values Duration
(Y value)
A 0, 4, 8, 12 1 day
B 1, 5, 9, 13 2 days
C 2, 6, 10, 14 3 days
D 3, 7, 11, 15 4 days

Whenever Pokérus spreads from an infected Pokémon to a new Pokémon, the new Pokémon inherits the infected Pokémon's strain of Pokérus (X) and Y is set to the default value for that strain. As an example, if a Pokémon has Pokérus with an X value of 7 and a Y value of 2 (2 days remaining before it will be cured) and it infects another Pokémon, the new Pokémon will get Pokérus with an X value of 7 and a Y value of 4 (4 days before it will be cured).

X values of 0 are not legitimate, since upon being "cured" the Pokémon would appear to have never had Pokérus at all.

Differences between generations

In Generation II

When the player first encounters the virus in one of the Generation II games, the nurse at the Pokémon Center will make note of it when the Pokémon is first healed after contracting it, saying that there are "small life forms" on the Pokémon. After leaving the Pokémon Center, Professor Elm will call the player to tell them that the virus has no effect and will wear off. A Pokémon with active Pokérus will list its status as such, and a Pokémon that has had Pokérus and is cured will have a small dot near its HP meter on the status screen.

If a Pokémon with any stage of Pokérus (active or cured) is traded back to a Generation I game, or withdrawn from Pokémon Stadium 2 by a Generation I game, all traces of that Pokémon having had Pokérus will disappear. This is because a Pokémon's Pokérus status is not saved in any form in the Generation I games, thereby making it possible for a Pokémon to legitimately contract Pokérus multiple times by trading it back and forth, once it becomes cured of a given infection. The only benefit of doing so would be to allow other Pokémon to contract the virus.

Nurse's comments

"Your Pokémon appear to have tiny life forms stuck to them.
Your Pokémon are healthy and seem to be fine.
But we can't tell you anything more at a Pokémon Center.
"

Elm's explanation

"Hello, <player>?
I discovered an odd thing.
Apparently there's something called Pokérus that infects Pokémon.
Yes, it's like a virus, so it's called Pokérus.
It multiplies fast and infects other Pokémon too. But that's all.
It doesn't seem to do anything, and it goes away over time.
I guess it's nothing to worry about. Bye!"

In Generation III

The Pokérus operates in much the same way as in Generation II, though it can infect Eggs too. Also, it can only be contracted or cured in Ruby, Sapphire, and Emerald. In FireRed and LeafGreen, as well as Colosseum and Pokémon XD, since the time function is absent, a Pokémon with Pokérus will keep it indefinitely (it can't spread Pokérus, either), until it is transferred to the Hoenn-based games.

Nurse's comments
A player being told their Pokémon has caught Pokérus

"Your Pokémon may be infected with Pokérus.
Little is known about the Pokérus except that they are microscopic life-forms that attach to Pokémon.
While infected, Pokémon are said to grow exceptionally well.
"

In Generation IV

The mechanics remain the same from Generation III. Additionally, much like storage in Pokémon Box Ruby & Sapphire and in the PC, storage in My Pokémon Ranch will keep a Pokémon's Pokérus status indefinitely. Starting in this Generation, Pokérus will double the EVs obtained from the EV-enhancing items.

In HeartGold and SoulSilver, Professor Elm calls the player a little while after healing their first Pokémon with Pokérus and tells them that it has no effect and will wear off. If he is called back, he will claim that Pokémon will level up better with the Pokérus while infected.

Nurse's comments

"Your Pokémon may be infected with the Pokérus.
Little is known about the Pokérus except that they are microscopic life-forms that attach to Pokémon.
While infected, Pokémon are said to grow exceptionally well.
"

Elm's explanation

When calling the player: "Hello, <player>?
I discovered an odd thing.
Apparently there's something called Pokérus that infects Pokémon.
Yes, it's like a virus, so it's called Pokérus.
It multiplies fast and infects other Pokémon too. But that's all.
It doesn't seem to do anything, and it goes away over time.
I guess it's nothing to worry about. Bye!
"

When called by the player: "Hello, <player>?
It seems that Pokémon that have been infected with Pokérus level up better.
We're not quite sure why..."

In Generation V

The mechanics remain more or less the same, but now the icon that appears if a Pokémon has previously had Pokérus is pinkish in color instead of the former yellow/orange color.

Pseudorandom number generation

To determine if any Pokémon in the player's party is to be infected, the game calls the Mersenne twister table to get a 32-bit random number, discards the lowest 16 bits, and then discards the highest two bits (a bitwise and with 0x3FFF). If this number is 0, the game will choose a Pokémon in the party to be infected.

To determine what party member is to be infected, the game takes another value from the Mersenne twister table, multiplies it by the party count, then discards the lowest 32 bits of the result. If this number is an Egg, the calculation is repeated. Otherwise, if that party member has already been infected, nothing else will happen.

If a Pokémon will be infected, the game takes the next value from the Mersenne twister table and discards the lowest 24 bits (if the lowest three bits of this result are all 0, another number is chosen). If any of the highest four bits are nonzero, the highest five bits are discarded. The resulting number will be X, the Pokérus strain; the duration of the virus will be set to X modulo 4 + 1.

These calculations mean that the strains 0 and 8 will never occur, and that the remaining strains are biased towards the lower numbers (with 1 through 7 being much more common than 9 through 15).

Nurse's comments

"Oh... It looks like your Pokémon may be infected with the Pokérus.
Little is known about the Pokérus, except that it is a microscopic life-form that attaches to Pokémon.
While infected, Pokémon are said to grow exceptionally well.
"

In Generation VI

In Generation VI, Pokérus does not affect EVs gained from Super Training. However, it increases the rate of Double-Up Bags that are received during the training regimen. The icon that appears if a Pokémon has Pokérus has been changed to spell out the full word, while the cured icon uses a design similar to the Gen V icon, with the mouth and eyes having a white color.

Nurse's comments

"Oh... It looks like your Pokémon may be infected with the Pokérus.
Little is known about the Pokérus, except that it is a microscopic life-form that attaches to Pokémon.
While infected, Pokémon are said to grow exceptionally well.
"

Status icons

050Diglett.png This section is incomplete.
Please feel free to edit this section to add missing information and complete it.
Reason: Generation VI icons.
PokérusIC Stad 2.png PokérusIC III.png PokérusIC IV V.png
Icon from
Stadium 2
Icon from
Generation III
Icon from
Generations IV and V
PokérusIC II cured.png PokérusIC Stad 2 cured.png PokérusIC III cured.png PokérusIC IV cured.png PokérusIC V cured.png
Cured icon from
Generation II
Cured icon from
Stadium 2
Cured icon from
Generation III
Cured icon from
Generation IV
Cured icon from
Generation V

In the anime

In Oaknapped, Dr. Namba explained to Professor Oak that the mysterious viral lifeform Pokérus is an important component of the Pokémon Power Acceleration Project (PPAP), a secret project that aims to infect Pokémon with Pokérus to evolve them at a faster rate. However, all of his specimens have died out. Professor Oak also explains that the term "Pokérus" was coined by combining the words "Pokémon" and "virus" together. Later, Professor Oak began researching about the Pokérus and Team Rocket's true intentions of using it.

In the manga

In the Pokémon Adventures manga

Pokérus was discussed in Alternate Dimension Showdown IX, when Platinum's team was discovered to have this virus and, as a result, became stronger. Her Froslass, Pachirisu, and Cherrim had it prior to being taken from the hospital, and then it spread to the rest of her party. At the hospital, Daisy Oak and Yanase Berlitz realize that the infection is, in fact, Pokérus.

Trivia

  • Pokérus is an example of a mutualistic virus, in which both host and virus benefit.


Project Games logo.png This game mechanic article is part of Project Games, a Bulbapedia project that aims to write comprehensive articles on the Pokémon games.