Pokérus

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.

In the games

Unlike other status conditions, Pokérus cannot be healed at a Pokémon Center or with any status condition healing item, and can only be obtained by the Pokémon in question once. 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.

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.

In later generations, the Pokérus became more accessible, with worldwide trading facilitated by the Nintendo DS's Wi-Fi capabilities beginning Generation IV. In fact, it is common courtesy to infect Pokémon to be traded on the Global Trade Station with Pokérus within some parts of the fandom. Also, a Pokémon's chances of being infected with the virus somewhat increase when a Pokémon has been traded from another game.

Infection

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 replaced. 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 onwards, 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), or My Pokémon Ranch (in Generation IV) before midnight. The game also recognizes immunizing if the system is turned off and on again on the next day.

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.

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.

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!"

Technical information

In Generation II, Pokérus is stored in a Pokémon's data structure as a single byte at offset 0x1C. When represented in hexadecimal format as XY, the upper 4 bits of the byte, X, represent the specific strain of Pokérus the Pokémon has contracted and 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 non-zero value. If Y (days remaining) is non-zero when X is also non-zero, this means the Pokémon is currently infected. If Y is 0 and X is non-zero, 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).

Erasing Pokérus from a Pokémon

If a Pokémon with any stage of Pokérus (active or cured) is traded back to a Generation I game, or withdrawn from 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.

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, and 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.

It will also double the effects of the new EV increasing items as well.

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, sharing similarity to the strain phenomenon in Generation II. However, a difference would be that the icon that would appear if a Pokémon has previously had Pokérus would be a pinkish color instead of the former yellow/orange color.

To determine if any Pokémon in the player's party is to be infected, the game calls the Mersenne twister table (random-number generator) and then discards the lower half (16 bits) of the 32 bit number, then does & 0x3FFF (a bitwise and) on the result (i.e. it discards the first two bits). If the result is 0, a Pokémon in the party will 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 that party member already has been infected, nothing else will happen.

Now that the given Pokémon is to be infected, the game takes the next value from the Mersenne Twister table, discards the lower 24 bits, then enters a loop to determine the strain. The strains are biased towards the lower number strains. Once a strain has been determined, the duration the infection will last is determined. For a given strain s, the duration is s+s%4.

Refer to the Generation II table for strains and duration, as it is exactly the same. However, strains 0x0 and 0x8 are not obtainable legitimately.

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 effort values gained during Super Training. Although it doesn't directly affect the amount of effort values gained during Super Training, it does however increase the rate of Double-Up bags that are received during the training regimen.

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

	Icon from Stadium 2	Icon from Generation III	Icon from Generations IV and V
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 (while seemingly oxymoronic, a "virus" is classified by infecting cells, rather than negative effects), in which both host and virus benefit. Viruses with possible positive effects exist in the real world, but all of Pokérus's known effects are objectively positive. A notable difference between biological viruses and the Pokérus is that biological viruses infect a host cell by mutating the cell's DNA. Pokérus only affects the host Pokémon's effort values, not the host's individual values, which are regarded as the Pokémon analogue to DNA.
• Prior to Generation VI, the chance of encountering a Shiny Pokémon with Pokérus is 1/178,956,971.

References

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