Did the Evidence Meet the WHO’s Standard for Establishing Causation?
The ViroLIEgy Boosters* series delivers a quick, potent dose of critical thinking—short, fast-acting pieces drawing from studies, reports, and archived findings. Designed to surface critical material in real time, they function as a rapid-response layer for ongoing documentation and conceptual refreshers, with primary sources for those who want to dig deeper.
Fast-moving insights. Ongoing documentation. Future deep dives in the making.
*Side Effects of this Booster may include: heightened awareness of shifting scientific goalposts, allergic reactions to historical inconsistencies, confusion when four postulates suddenly become six, and a persistent inability to accept conclusions without examining the evidence.
One of the arguments I regularly encounter pushback on is when I cite the WHO’s March and April 2003 statements on SARS, which clearly identified Koch’s Postulates as necessary criteria for establishing that a microorganism causes disease—including for so-called “viruses.”
Critics commonly argue that Koch’s Postulates were developed specifically for bacteria and therefore cannot be applied to “viruses.” Instead, they contend that modified criteria must be used to establish “viral” causation.
But is that what the WHO actually said in 2003? And did the WHO invoke Koch’s original four Postulates or some modified version of them?
For those unfamiliar, Koch’s Postulates are a set of four criteria traditionally attributed to German bacteriologist Robert Koch in the late 19th century. They were developed to establish a causal relationship between a microorganism and a specific disease. Since their introduction, they have served as the gold standard for demonstrating microbial causation.
I have provided material demonstrating the importance of satisfying Koch’s Postulates from numerous organizations, including the CDC, NIH, and AAI, as well as from textbooks, microbiologists, and even virologists themselves. However, the specific statements made by the WHO seem to generate the most controversy. I have encountered arguments claiming that these statements were merely part of a press release intended for the general public, that the WHO was using the term Koch’s Postulates in name only, or that the statements applied exclusively to SARS.
So, in an effort to clear up the confusion as much as possible, let’s travel back in time to 2003. By examining the WHO’s own statements, the people involved, and the scientific publications that followed, let’s see if we can shed some light on this situation and determine what the WHO really meant when it referred to Koch’s Postulates.
The Timeline
March 12, 2003 — WHO Issues a Global Alert About Cases of Atypical Pneumonia
The WHO issued a global alert concerning outbreaks of severe atypical pneumonia reported in Hanoi, Hong Kong, and Guangdong Province, China. The initial illness was “flu-like,” with a rapid onset of high fever followed by muscle aches, headache and sore throat. In some, but not all cases, the initial symptoms were followed by bilateral pneumonia, with some progressing to acute respiratory distress requiring assisted breathing on a respirator. At the time, the cause had not been established, and specimens were still undergoing laboratory investigation.
March 15, 2003 — WHO Issues Emergency Travel Advisory
The WHO issued an emergency travel advisory after receiving reports of more than 150 new suspected SARS cases across several countries, including Canada, China, Hong Kong, Singapore, Thailand, and Vietnam. Dr. Gro Harlem Brundtland, Director General of the World Health Organization at the time, stated that SARS was a “worldwide health threat” and that the “world needs to work together to find its cause, cure the sick, and stop its spread.”
March 17, 2003 — WHO Coordinates International Effort to Identify and Treat SARS
The WHO announced an expanded international effort to investigate SARS, involving 11 laboratories across 10 countries, coordinated through its Global Outbreak Alert and Response Network. The multicenter effort aimed to identify the causative agent of the atypical pneumonia cases labelled as SARS.
March 22, 2003 — WHO Announces “SARS Virus Isolated”
The WHO announced that researchers at the University of Hong Kong had successfully isolated and cultured a “virus” from the lung tissue of a SARS patient. The announcement opens with the claim that the researchers had achieved “success in culturing the viral agent that causes Severe Acute Respiratory Syndrome (SARS).” Yet, later in the very same announcement, the WHO acknowledges that the “race to identify the SARS causative agent is by no means over” and that, despite the reported isolation, the agent’s “identity remains elusive.”
March 27, 2003 — WHO Update 12: “SARS Virus Close to Conclusive Identification”
The WHO reported that international laboratory investigations increasingly pointed to a “coronavirus” as the primary cause of SARS:
“Data from many network laboratories indicate that a coronavirus is the primary cause of the disease,” said WHO virologist and epidemiologist Klaus Stöhr. “This virus is unlike any known human or animal member of this virus family. It is consistently found in specimens from SARS patients from many countries. It has been isolated in cell-culture. We are very close to knowing for sure.”
However, the WHO also acknowledged that additional experiments were still required before the agent could be conclusively identified. In this same announcement, the organization explicitly identified Koch’s Postulates as the necessary standard for establishing causation:
“Conclusive identification of a causative must meet all criteria in the so-called “Koch’s postulate.” The additional experiments needed to fulfil these criteria are currently under way at a laboratory in the Netherlands.”
This was a direct statement from the WHO that, in order to conclusively prove that a microbe is the cause of disease, Koch’s Postulates must be satisfied.
April 3, 2003 — New Scientist: Identity of Killer Pneumonia Bug Confirmed
New Scientist reported that the novel “coronavirus” had to satisfy Koch’s Postulates to be definitively declared the cause of SARS. The article quoted collaborating virologist Dr. Albert Osterhaus, who claimed that the third Postulate had been fulfilled through animal “infection” experiments:
Now Osterhaus has cracked Koch’s third, and toughest postulate. “We have infected an animal,” he says. He will not yet reveal what kind, but says he has tested the virus in primates and mice. Besides showing the virus is the pathogen, says Osterhaus, the infected animals can now be used to screen antiviral drugs.
April 7, 2003 — David Heymann: Koch’s Four Postulates
Just 11 days after the WHO’s March 27 announcement, David L. Heymann, M.D., then WHO Executive Director for Communicable Diseases, addressed the U.S. Senate Committee on Health, Education, Labor, and Pensions during a hearing on the SARS threat.
In his prepared statement, Heymann explained the purpose of the international laboratory network established on March 17 and identified the scientific criteria the participating laboratories were expected to fulfill:
“On 17 March, a network of 11 leading laboratories around the world was set up as a mechanism for expediting identification of the SARS causative agent. Laboratories were selected on the basis of three criteria: outstanding scientific expertise, facilities at biosafety level III, and capacity to contribute to the battery of tests and experiments that would be needed to fulfill Koch’s four postulates for the identification of an infectious agent as the cause of a specific disease.”
Heymann was not simply discussing Koch’s Postulates in passing. He was describing to the Senate the specific scientific requirements that the WHO’s international laboratory network had been established to help fulfill. In his statement, he clearly referred to Koch’s four postulates, and he described their purpose in unmistakably broad terms: identifying an “infectious” agent as the cause of a specific disease.
April 11, 2003 — WHO Update 27: “One Month into the Global SARS Outbreak”
Reiterating the points made in his Senate testimony four days earlier, David Heymann reaffirmed that the international laboratory network established on March 17 was tasked with conducting the experiments necessary to fulfill Koch’s four postulates and identify an “infectious” agent as the cause of a specific disease:
On 17 March, a network of 11 leading laboratories around the world was set up as a mechanism for expediting identification of the SARS causative agent. Laboratories were selected on the basis of three criteria: outstanding scientific expertise, facilities at biosafety level III, and capacity to contribute to the battery of tests and experiments that would be needed to fulfill Koch’s four postulates for the identification of an infectious agent as the cause of a specific disease. The network was set up on the model of the influenza network and provides another important lesson: models and systems set up for one health emergency can be rapidly adapted to serve others.
Heymann also acknowledged that, despite identifying a suspected causative agent, the WHO did not yet have conclusive proof that the newly discovered “coronavirus” caused SARS. Results from animal experiments were still pending and were expected to provide the remaining evidence needed for definitive proof:
Nonetheless, we still do not have conclusive proof that the new virus is indeed the cause of SARS. The results of animal experiments, which are currently being conducted by a laboratory in a WHO network, will be available soon and may provide the last pieces of evidence needed for definitive proof that SARS is caused by the newly discovered coronavirus. Furthermore, the findings will provide additional evidence to understand the role of metapneumovirus as a possible “helper virus” in persons co-infected with the new coronavirus.
April 16, 2003 — WHO Update 31: Koch’s Postulates Fulfilled
Five days later, the WHO officially announced that a previously unidentified human “coronavirus” had been established as the cause of SARS, crediting an unprecedented international collaboration involving 13 laboratories across 10 countries:
Today, the World Health Organization announced that a new pathogen, a member of the coronavirus family never before seen in humans, is the cause of Severe Acute Respiratory Syndrome (SARS). The speed at which this virus was identified is the result of the close international collaboration of 13 laboratories from 10 countries. While many lines of evidence have found strong associations between this virus and the disease over the last weeks, final confirmation came today.
“The pace of SARS research has been astounding,” said Dr. David Heymann, Executive Director, WHO Communicable Diseases programmes. “Because of an extraordinary collaboration among laboratories from countries around the world, we now know with certainty what causes SARS.”
The update credited Dr. Albert Osterhaus and his team at the Erasmus Medical Center in Rotterdam with completing the work necessary to establish the “coronavirus” as the cause of SARS:
“Today, the first part of the mission of our network has been fulfilled, as researchers have both detected a hitherto unknown virus and established it as the cause of SARS. The new coronavirus has been named by WHO and member laboratories as “SARS virus, ” said Dr Albert Osterhaus, the Director of Virology at Erasmus Medical Center in Rotterdam. Erasmus completed the work to definitely prove that the new coronavirus causes SARS.
The WHO once again addressed the criteria that the international laboratories were working to satisfy: Koch’s Postulates.
However, this time the organization explicitly listed the four conditions considered necessary to claim any agent as the cause of disease:
Over the past three weeks, due to the urgency surrounding the worldwide threat to health of SARS and early indications this was a new member of the coronavirus family, research has proceeded under the assumption that SARS was caused by a new coronavirus.
The 13 laboratories have been working on meeting Koch’s postulates, necessary to prove disease causation. These postulates stipulate that to be the causal agent, a pathogen must meet four conditions: it must be found in all cases of the disease, it must be isolated from the host and grown in pure culture, it must reproduce the original disease when introduced into a susceptible host, and it must be found in the experimental host so infected.
For reference: The WHO also published this announcement under its official communications contact, identifying Dick Thompson as Communication Officer for Communicable Disease Prevention, Control and Eradication at WHO headquarters in Geneva.
April 16, 2003 — Albert Osterhaus: “Those Four Things Have Been Fulfilled”
The WHO’s April 16 press briefing provided further clarification about the claim that Koch’s Postulates had been fulfilled. During the briefing, WHO virologist Klaus Stöhr identified Dr. Albert Osterhaus and his team at Erasmus Medical Center in Rotterdam as having conducted the final animal experiments needed to complete the investigation:
“I would like to continue with Dr Osterhaus. Dr Osterhaus is the one, he and his colleagues, who have been adding the final piece to the puzzle of research that took place during the past five weeks. His team has conducted the trials in monkeys with the coronavirus. He is the one who reported this morning that the Koch’s postulates have been fulfilled. We can now with all confidence say that the causative agent of SARS is the coronavirus first detected in Hong Kong on 21 March 2003.”
Osterhaus then explained how the four Postulates had been assessed:
“The Koch’s postulates are firstly that the agent should be present in basically all the individuals that are suffering from the disease. That holds true predominantly for the coronavirus and not for the metapneumovirus because it is less than 50% of the people infected or having SARS that were infected with metapneumovirus. The second postulate is that you should be able to cultivate the virus. That holds true for the two viruses.
The third postulate is that you should be able to reproduce the disease in the host or a related host. That is what we have done for the coronavirus, and coronavirus only. The last postulate then is that you should be able to reisolate the virus back from the animals that you have infected with that virus. Those four things have been fulfilled for coronavirus and only three of those for the metapneumovirus.”
Osterhaus did not simply state that Koch’s Postulates had been fulfilled. He clearly described how he believed each of the four conditions had been satisfied.
May 2003 — WHO Bulletin: The 13 Laboratories’ Objective Was to Meet Koch’s Four Postulates
In its May 2003 issue (Volume 81, Issue 5, page 384), the Bulletin of the World Health Organization published an account of the April 16 announcement that a previously unidentified human “coronavirus” had been established as the cause of SARS.
The report specifically addressed the work of the 13 collaborating laboratories across 10 countries, clearly stating that their objective had been to satisfy Koch’s four postulates for establishing microbial causation:
“The objective of the 13 laboratories was to meet Koch’s four postulates for proving the identity of a disease’s causal agent: it must be found in all cases of the disease; it must be isolated from the host and grown in pure culture; it must reproduce the original disease when introduced into a susceptible host; and it must be found in the experimental host so infected.”
Contemporary Media and Scientific Publications
The WHO’s April 16 announcement was widely reported in the international media, with numerous outlets repeating the claim that Koch’s four Postulates had been fulfilled and that the “coronavirus” had been established as the cause of SARS. The following reports and publications provide a snapshot of how this announcement was presented and understood at the time.
The Intelligencer / Associated Press — April 15, 2003
Scientists Confirm Virus As Cause of SARS
Scientists had been almost certain the new form of coronavirus first isolated from sick patients March 21 by the University of Hong Kong was the cause of SARS. But they could not say for sure until they had satisfied what is known as Koch’s postulates _ four scientific tests that verify whether a virus causes a certain disease.
“The Koch’s postulates have been fulfilled, so we can now say for certain that the new coronavirus is the cause of SARS,” said Dr. Klaus Stohr, a World Health Organization virologist who is coordinating the scientists’ work.
The first test requires that the virus be found in all the sick people, but not in healthy people. The second isolates the virus from a sick patient and shows that it multiplies in a lab dish.
The third step uses the virus from the petri dish to make a lab animal sick with the same disease as that seen in humans. The final step requires isolating the SARS virus from the sick lab animal and showing it can grow in a petri dish.
A team led by Dr. Albert Osterhaus, the director of virology at Erasmus Medical Centre in Rotterdam, Netherlands, carried out the final two verifying steps.
The Washington Post — April 16, 2003
Scientists Identify Cause of Outbreak
“For a virus to be conclusively linked to a disease, it must satisfy four criteria, known as Koch’s postulates:
The microbe must be found in all patients with the disease; it must be isolated from a patient and grown in the laboratory; it must reproduce the disease in an animal; and it must be found in that animal.”
CIDRAP News — April 16, 2003
New Coronavirus Confirmed as SARS Pathogen
“Investigators at Erasmus Medical Center in Rotterdam, Netherlands, completed the research to fulfill Koch’s postulates, the four conditions for proving disease causation, WHO officials said. The WHO announcement gave no details on the conclusive research, but reports elsewhere said investigators infected monkeys with the coronavirus and observed that they developed an illness that looked like SARS.”
“In recent days health officials had been increasingly confident that the new coronavirus causes SARS, but until now the virus had not been shown to reproduce the disease in an animal host. As explained in the WHO announcement, Koch’s postulates state that to be confirmed as the cause of a disease, an organism must be found in all cases of the disease, it must be isolated from the host and grown in pure culture, it must reproduce the disease when introduced into a susceptible host, and it must be found in that infected host.”
Los Angeles Times — April 17, 2003
Dutch Scientists Prove Virus Is Cause of SARS
Although most experts have been convinced that SARS is caused by the new coronavirus — whose genetic blueprint was identified Sunday by a Canadian laboratory and Monday by the CDC — actual proof requires fulfilling four conditions known as Koch’s postulates. To identify a virus as the source of a disease, scientists must show that it is present in all cases of the disease; that it can be isolated from the host and grown in the laboratory; that it can produce symptoms of the original disease when introduced into a susceptible animal host; and that it can be isolated again from that animal.
A team led by Dr. Albert Osterhaus of the Erasmus Medical Center in Rotterdam, the Netherlands, said Monday they had fulfilled the last two postulates. They placed the virus in the noses of monkeys and found that the animals developed symptoms similar to those exhibited by humans with SARS. Lung tissues from the monkeys showed damage similar to that found in humans as well.
They then were able to isolate the virus from the monkeys and grow it in laboratory dishes, fulfilling all of Koch’s postulates.
Genome Biology — April 17, 2003
WHO Says Coronavirus Causes SARS
The organization claimed that its collaborating laboratories have concluded the coronavirus meets all four of “Koch’s postulates” for a causative agent: it must be found in all cases of the disease, it must be isolated from the host and grown in pure culture, it must reproduce the original disease when introduced into a susceptible host, and it must be found in the experimental host so infected.
The key to this announcement were the last two tests, performed in monkeys by Albert Osterhaus and colleagues at the Erasmus Medical Centre in Rotterdam, one of WHO’s global collaborative research network, which now consists of 13 laboratories.
Dawn — April 17, 2003
WHO Confirms Coronavirus as Cause of SARS
The confirmation came at a meeting of top researchers from 13 laboratories around the world at WHO headquarters in Geneva, the organisation’s chief researcher on Severe Acute Respiratory Syndrome (SARS), Klaus Stohr, told journalists.
“These colleagues have come to consensus agreement that we can now say that the disease called SARS first reported on March 12 is being caused by the coronavirus,” Stohr said.
The confirmation came after a laboratory at Rotterdam’s Erasmus University in the Netherlands managed to fulfil four key conditions to identify the virus in testing with animals, known as the “Koch postulates”.
The New York Times: Koch’s Postulates and the SARS Announcement — April 16–17, 2003
Interestingly, on April 16, 2003, the same day the WHO announced that a new “coronavirus” had been established as the cause of SARS, The New York Times published an article titled The Microbe Test, explaining Robert Koch’s four Postulates for establishing microbial causation. While the article did not specifically address SARS or the WHO announcement, its publication on the very same day the WHO proclaimed that Koch’s Postulates had been fulfilled is an interesting “coincidence.”
Also on April 16, the NYT published Respiratory Illness: Virus Experiments; Monkeys at Zero for Cause of Mysterious Disease, explicitly connecting Koch’s Postulates to the SARS investigation:
“The monkey experiments are essential in fulfilling the steps known as Koch’s postulates that are needed to establish proof that a virus or other microbe causes a disease.”
The article further explained that scientists needed to determine whether injecting the “coronavirus” into animals produced symptoms similar to those experienced by humans.
The following day, April 17, the NYT published The SARS Epidemic: The Virus; Health Group Certain of Agent in Respiratory Ailment, reporting the WHO’s declaration that the new “coronavirus” had been conclusively established as the cause of SARS:
“Ending a monthlong hunt for the cause of severe acute respiratory syndrome, the World Health Organization said yesterday that animal experiments had proved conclusively that the agent was a new member of the coronavirus family.”
“The conclusive evidence came from monkey experiments conducted in recent days by Dr. Albert Osterhaus, the head of virology at Erasmus University in Rotterdam.”
May 15, 2003 — Koch’s Postulates Fulfilled for SARS “Virus”?
From official WHO updates, press releases, Senate hearings, press conferences with the virologists themselves, and contemporary media coverage, it is clear that Koch’s four Postulates were the explicit criteria invoked to establish that the “novel coronavirus” caused SARS.
About a month after the global announcement, the formal study describing this work was published in Nature (Vol. 423, May 15, 2003) under the title Koch’s Postulates Fulfilled for SARS Virus.
However, something remarkable occurred between the WHO’s public announcements and the peer-reviewed publication of the trial results. In the very first sentence of the paper, the authors execute a pivotal shift. They state that according to Koch’s Postulates, as modified by Rivers, six criteria are required to prove a “virus” causes a disease:
According to Koch’s postulates, as modified by Rivers for viral diseases, six criteria are required to establish a virus as the cause of a disease1. The first three criteria — isolation of virus from diseased hosts, cultivation in host cells, and proof of filterability — have been met for SCV by several groups2,3,4,5. Moreover, of 96 individuals complying with the World Health Organization’s definition of SARS6 in Hong Kong, 86 (90%) yielded laboratory evidence of SCV infection.
We have tested for the three remaining criteria: production of comparable disease in the original host species or a related one, re-isolation of the virus, and detection of a specific immune response to the virus.
In the paper’s conclusion, the authors assert: “SCV thus fulfils all of Koch’s postulates as the primary aetiological agent of SARS.”
Did you see the switcheroo?
While the title and conclusion assert that Koch’s Postulates were fulfilled, the body of the paper instead attempted to satisfy Thomas Rivers’ modified criteria.
For context, in his landmark 1937 paper Viruses and Koch’s Postulates, virologist Thomas Rivers made a candid admission:
“It is obvious that Koch’s postulates have not been satisfied in viral diseases.”
Rivers then laid out his own substitute criteria for “viral” causation:
- Isolation of “virus” from diseased host
- Cultivation of “virus” in host cells
- Proof of filterability
- Produce same disease in host
- Re-isolation of “virus”
- Detection of a specific “immune” response to “virus”
These six criteria are fundamentally distinct from Koch’s original four rules of proof. Rivers himself acknowledged this in his conclusion:
“To summarize, it can be said that the cause of viral diseases is known and that Koch’s postulates as proposed by him do not have to be fulfilled in order to prove that a virus is the cause of a disease. However, the spirit of his rules of proof still holds in that a worker must demonstrate that a virus is not only associated with a disease but that it is actually the cause. The methods of doing this are different from the ones used by Koch but are equally efficient.”
While Rivers asserted that his criteria were “equally efficient,” they significantly lowered the bar for scientific proof. Rivers relaxed the requirement that the agent must be found in every case of disease, accommodated healthy/asymptomatic carriers, abandoned the requirement for pure culture, and accepted indirect markers (like “antibody” response) as surrogate proof.
As the frameworks presented by Koch and Rivers are clearly distinct, they should not be treated as equivalent. Thus, the paper published by the WHO’s international collaboration did not satisfy Koch’s Postulates—the very criteria that the WHO had established as necessary in the preceding months. The researchers instead used Rivers’ own criteria, a completely separate framework, and it can be argued that they failed to satisfy even those requirements (as detailed in my article Fouchier “SARS-COV-1” Paper (2003): Koch’s Postulates Fulfilled?).
For further insight, see Barbara Pfeffer Billauer’s 2014 paper, A Retrospective Review of Evidence of SARS Causation in Light of the MERS and Ebola Epidemics, which examines the evidence supporting the SARS causation claim and argues that Koch’s Postulates had not been satisfied in attempts to replicate it.
Conclusion: The WHO Statement Stands, But Koch’s Postulates Remain Unfulfilled
On May 23, 2003, a little over a week after the Nature paper was published, Science ran a profile on Albert Osterhaus titled The Virus Collector. Just as the WHO had done during March and April 2003, the first paragraph of the profile directly refers to Koch’s Postulates as the criteria Osterhaus and his team were tasked with fulfilling:
It was the study the world was waiting for. By early April, everybody suspected that a newly discovered coronavirus was the cause of severe acute respiratory syndrome (SARS). But to prove it, researchers had to infect animals with the virus, show that they got sick, and show that their bodies began producing the virus. In other words, they had to fulfill Koch’s postulates.
In 2006, the WHO published a retrospective, SARS: How a Global Epidemic Was Stopped, which reinforced its position. In its timeline, the WHO reiterated that Koch’s Postulates were fulfilled for “SARS-CoV.” Even more significantly, its glossary defines an aetiological agent as the specific agent that causes disease and states that “Koch postulates are used to establish the aetiological agent.” Thus, three years after the original investigation, the WHO was still directly connecting the establishment of an “infectious” agent as the cause of disease to Koch’s Postulates.
In 2012, while discussing MERS, Ron Fouchier, one of the principal virologists involved in the WHO collaboration, likewise stated that his team hoped to satisfy Koch’s Postulates for MERS, just as they had claimed to do for SARS:
“For starters, we’ll find out whether animals get sick from this virus. You can isolate a virus from a patient, but that does not mean they died from it; to show that it causes disease you need to fulfill Koch’s postulates. That’s what we did for SARS, and it’s what we hope to do here; we’ve applied for emergency ethical approval.”
The problem is that neither Osterhaus, Fouchier, nor anyone else involved ever satisfied Koch’s four Postulates as laid out by the WHO. To claim otherwise is entirely misleading. Anyone asserting that Koch’s Postulates contain six criteria is simply wrong. Those are Rivers’ Postulates, and they are not the same as the rigorous criteria attributed to Koch.
Based upon the available evidence, it is safe to conclude that:
- Koch’s Postulates were not only mentioned as part of a press release—they were discussed by leading members of the WHO investigation and in testimony submitted to the U.S. Senate.
- Koch’s Postulates were not merely mentioned in name only—the four requirements were deliberately laid out in detail.
- Koch’s Postulates were not simply invoked only for SARS. Fouchier himself referred to them again in 2012 when discussing the effort to establish MERS causation.
- The statements by the WHO clearly referred to Koch’s original four Postulates as the necessary steps to satisfy to conclusively prove any microbe is the cause of disease. Rivers’ six criteria were only introduced once the Nature paper was published. They are not interchangeable.
No statements by the organization since have ever walked back, contradicted, or replaced what the WHO presented back in 2003. Thus, the evidence stands that the WHO consider Koch’s four Postulates—not Rivers’ six—as the essential requirements to prove causation, even for so-called “viruses.”
And to this day, Koch’s Postulates remain unfulfilled.
