Fans ofCapcom’sResident Evilfranchise love its trademark brand of limited ammunition, zombies at every corner, and a ton of monstrous threats. Moreover, as players will soon learn, almost every outbreak in the series began as a project gone awry from folks at Umbrella Corporation, the de facto “evil organization” in the franchise. However, fans might remember that the games also have their fair share of alternate viruses outside the original T-Virus that plagued the first few games.
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In fact, eagle-eyed players might notice that some T-Virus spinoffs seem more dangerous than the original virus. Unfortunately, the forces behind these new strains also want to use them for their own nefarious ends. However, just which viruses in the franchise spark the most terror for players?
Updated on June 24, 2025 by Rhenn Taguiam:WithResident Evil 4 Remakeconfirmed for a 2023 release, it makes sense for fans of theResident Evilfranchise to brush up on their biohazard knowledge to better grasp the bioterrorism scene prevalent in the world of the franchise. Not only that, but knowing about more viruses in the franchise may give players a better grasp of howResident Evil 4’s Las Plagas works within the greaterResident Evillandscape.
To do this, fans may want to get to know other unknown viruses in the franchise, including additional strains of the T-Virus, as well as horrifying variants that may upend the global war on bioterrorism had they been left unchecked.
17Clay Virus
Unlike other virusesin theResident Evilfranchise, theClay Virusisn’t exactly “canon” to the series. Still, it serves as a rather important stepping stone to a virus featured in the story. At the same time,Resident Evilintroduces the mysterious Progenitor Virus as the ancient origins of the T-Virus and its subsequent evolutions. However, it was as far back asResident Evil 2andCode Veronicathat the idea was introduced as a concept, introduced byRE1andParasite Evescriptwriter Kenichi Iwao as theClay Virus.
Iwao’s vision of the Clay Virus was relatively short and was changed multiple times during Noburo Sugimura’s development inRE5. At its core, the Clay Virus supposedly has four (4) strains, each relatively associated with the T-Virus variants that led to early bosses and creatures in the franchise. These would include the A-Strain (leading to the Neptune shark-based BOW), the B1-Strain (for the Cerberus BOW), the B2-Strain (for the more intelligent Hunter), and the E-Strain for the virus that infected Arklay Laboratory’s staff.
16T-JCCC203
One of the most tragicbackstories in theResident Evilhorror seriesis the fact that the vicious T-Virus was partially originally designed as a cure for illnesses. Such was the case ofT-JCCC203, a variant of the T-Virus that was only referenced in theResident Evil Outbreakseries through its side stories. The T-JCCC203 was developed as an oncolytic virus targeting cancerous cells. It had illegally entered clinical trials through an unnamed front and had patients of a hospital in the Arklay Mountains act as test subjects.
Both of the virus’s first patients had their cancer cells killed by the virus but in exchange developed extreme appetites associated with zombification. While the first patient Doug Frost died three (3) days after being administered the drug, its second patient Dorothy Lester was consumed by a plant that became monstrous after being infected by T-JCCC203. Perhaps this virus had infected patients under the guise of an effective “curse” makes this horrifying, especially for patients like Lester’s husband. He only volunteered Dorothy to the trial out of desperation.
15E-Strain (T-Virus)
It could be remembered that the “quest” to transform the Tyrant Project into a means to lead to “the perfect human”throughout theResident Evilserieswas conducted by two (2) separate teams. It’s among the staff of the Arklay Laboratory that the prototypalE-Strainwas developed, partially due to how the B-Strain only led to the creation of the Cerberus zombie dogs. The main objective of the E-Strain is to transform a human into a supersoldier mutant while limiting brain damage to avoid ordinary zombification.
What’s perhaps terrifying about the E-Strain is how it ultimately led to a successful prototype, named T-002 that the STARS team fought inResident Evil. Another notable trait of E-Strain infected was a secondary mutation, transforming them into more powerful Crimson Heads after extreme injury. It was also the E-Strain that led to the creation of the Lickers, clawed and extremely agile creatures with tongues that can pierce flesh.
14Cameron Virus
One of the most bizarre viruses to appear in the franchise is one featured in material fans couldn’t immediately access. TheCameron Virusis a virus strain exclusively featured inBiohazard 4D-Executer, a short film currently shown in Mosaic Garden as a 3D-film experience. The film describes a team of commandos looking for Dr. Cameron trapped in Raccoon City, eventually leading to the deaths of all agents except Cameron herself.
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Despite the film only running for around 20 minutes and features some rather exaggerated action scenesreminiscent of pre-Resident Evil Remakegames, it was more than enough to reveal the terrifying nature of the virus. Instead of being a T-Virus variant, the Cameron Virus seems to be exclusive to the research of Dr. Cameron, with the virus capable of transferring a host’s consciousness to other creatures. Not only that, but the virus seems capable of giving the infected the ability to mutate other parts of their body, allowing them to grow spikes and tentacles for defense willingly.
13Plaga
Background details in the lore hinted that the Plaga parasites have come from as far as the Neolithic age’s Ndipaya Kingdom in West Africa. Additional information also reveals that Ganados performed human sacrifices associated with the Plaga as depicted in cave art. In turn, the Plaga may have arrived in Spain as far back as the Bronze Age.
Interestingly, it’s thanks to Osmund Saddler that the Plaga officially entered the bioweapons scene. Saddler, alongside the Los Illuminados, created a large research complex to study the Plaga and create new species. In turn, Saddler managed to create Dominant Plagas that didn’t change the host and commanded Recessive Plagas that controlled the host.
Unlike other viral strains, the Plaga parasite can exhibit minimal changes in its host’s appearance and instead affect its central nervous system. If a Plaga and its host survive, the latter receives mutations in the form of enhanced durability and strength - to the point of sustaining gunshot wounds. It’s observed that Plaga themselves use ultra-high frequency sound waves to communicate with each other. Being a “natural” parasite, it’s unknown if it’s possible to rid the world of Plaga for good.
12Mold
Dr. Miranda stumbled upon a fungal superorganism in a European Village back in the 1900s in an effort to revive her daughter Eva, who had just died from the Spanish flu. Upon its discovery, Miranda observed that the fungus - which she called the Mold - can store both genetic information and memories of organisms it can assimilate. Her research would have her attempt to create a “vessel” for a resurrected Eva. Meanwhile, she gave a sample of the Mold to the Connections for their own bioweapons project.
Over the years, the Mold proved quite effective towards the Connections’ BOW efforts. Due to its properties, the Mold can effectively “control” the minds of its victims - capable of transforming hostile enemies into allies. Of its many variants, the E-Type - eventually Eveline - became the most successful. As observed, the E-Type can use its fungal filaments to create new superorganisms (Molded). Initial infection would have the fungus spread inside its host, granting it regenerative abilities. Later stages of infection would slowly grant them superhuman physique at the cost of degrading mental states. When the fungus has completely infected its host, the physical form becomes unrecognizable and the mind lost.
When Ethan synthesized the E-Necrotoxin compound, he managed to kill Eveline - the only E-Type in existence. It’s unknown whether The Connections has more hidden variants of the Mold or copies of Eveline’s genetic data.
11Cadou
While Mother Miranda gave samples of the Mold to the Connections, she also worked on her own experiments with the Mold. Dubbed the Cadou, Mother Miranda orchestrated this organism’s creation after exposing the Mold to a parasitic nematode.
Miranda’s research notes didn’t reveal much about the actual mode of implantation with regards to the Cadou. However, it’s implied that Cadou can infect hosts via implantation, direct injection, or even spreading wounds.
Interestingly, the Cadou seems to exhibit very flexible properties. This is evident when Miranda implanted the Four Lords with the Cadou, which spawned into different abilities. Their experiments further led to new variants of the Cadou. These included bat-like Moroaica and powerful Witches (Dimitrescu), or cybernetic Soldats and Haulers (Heisenberg). Lycans can become more powerful Varcolac (Moreau), or even get to control Cadou-infected hosts from afar (Beneviento).
10T-Virus
Interestingly enough, the most popular variant of theResident Evilvirus may turn out to be its least lethal. The T-Virus serves as the template for most of the other viruses in the games. In essence, the T-Virus weaponized the Progenitor Virus, bringing out its resurrection qualities and amplifying the aggression and cannibalistic tendencies of the infected.
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As a viral agent, Umbrella originally designated the T-Virus as a means to bring their eugenics program - the Wesker Project - into fruition. Instead of resorting to using an army, Umbrella created the T-Virus specifically to infect large populations quickly and have a 100-percent mortality rate. However, Umbrella soon incorporated the T-Virus into the Tyrant Program after discovering a natural immunity amongst 10-percent of any population. This T-Virus spinoff intended to create powerful humanoid weapons (soon BOWs) to kill the surviving populace.
However, thanks to the extensive studies and researches conducted on the T-Virus, it’s also one of the easiest viruses to counteract. Moreover, the development of the Daylight Vaccine made the T-Virus the least harmful of the viral agents in the game. Lore-wise, this Daylight Vaccine became part of the standard treatment procedure of outbreaks.
9Chimera Virus
Dr. Robert Chan developed the Chimera Virus as a solution to the T-Virus and its uncontrollable mutations. With the Chimera Virus, T-Virus infected can now mutate through sheer willpower. This ability will be due to the fact that the Chimera Virus also comes with a means of triggering the part of the human genome that “strives for perfection.”
Unfortunately, not much is known about the Chimera Virus except for its appearance in theBIOHAZARD to the Libertylight novel. Moreover, more potent virus strains began appearing soon afterward.
Chimera Virus creator Dr. Robert Chan’s Chan Industries is a subsidiary of Umbrella Corporation, which may explain his acquisition of a T-Virus sample.The Chimera Virus also marks the first appearance of a “C-Virus” prior to the Chrysalid Virus.
8Prototype Virus
Fans ofResident Evilmay fondly remember black-clad Albert Wesker and his pair of sunglasses. Moreover, others might call haxx whenever Wesker showed off his incredible strength, speed, and durability against the franchise’s heroes. Thanks toResident Evil 5, players put a stop to Wesker’s plans once and for all. However, fans mistakenly say Wesker has the Uroboros Virus. In fact, his abilities stemmed from the Prototype Virus, a T-Virus strain that Wesker and other selected participants of Project Wesker had to take.
Thanks to the Prototype Virus, successful recipient-survivors developed incredible strength and endurance, speed and agility, as well as a healing factor. Apparently, the Prototype Virus only affects lower organs and muscle tissues. Meaning, the lack of impact to the brain keeps the subject’s intellect intact. Due to the strain the Prototype Virus had on ordinary subjects, only specially-cultivated members of Project W (the Wesker Children) can even attempt to take it.
As part of Umbrella’s eugenics project, the Prototype Virus tested whether particular Project W candidates had the “markers” needed for human evolution. If they don’t, they die from the virus. However, Albert and Alex Wesker survived, with the Prototype Virus giving them more than enough superhuman abilities. Unfortunately, despite the danger the two posed, the difficulty in searching for compatible hosts made the Prototype Virus useless.
