Bat SARS-like coronavirus: It’s not SARS 2.0!

SARSA study on the potential of SARS-virus-like bat coronaviruses to cause human disease has reawakened the debate on the risks and benefits of engineering viruses. Let’s go over the science and then see if any of the criticisms have merit.

The SARS epidemic of 2003 was caused by a novel coronavirus (CoV) that originated in bats. Results of sequence analyses have shown that viruses related to SARS-CoV continue to circulate in bats, but their potential for infecting humans is not known. One can learn only so much from looking at viral sequences – eventually experiments need to be done.

To answer the question ‘do the SARS-CoV like viruses circulating in bats have the potential to infect humans’, a recombinant virus was created in which the gene encoding the spike glycoprotein of SARS virus was swapped with the gene from a bat virus called SHC014. The SARS-CoV that was used (called SARS-MA15) had been previously passaged from mouse to mouse until it was able to replicate in that host. The use of this mouse-adapted virus allows studies on viral disease and its prevention in a mammalian host.

The recombinant virus, called SHC014-MA15, replicated well in a human epithelial airway cell line and in primary human airway epithelial cell cultures. The recombinant virus replicated just as well as the Urbani strain of human SARS-CoV. This result was surprising because the part of the spike protein of SCH014 that binds the cell receptor, ACE2, is sufficiently different from the SARS-CoV spike, suggesting that the virus might not infect human cells.

First lesson learned: looking at a viral genome sequence alone does not answer all questions. The spike glycoprotein of a bat coronavirus can mediate virus entry into human cells.

Next the authors wanted to know if SHC014-MA15 could infect mice and cause respiratory disease. Ten week old mice were infected intranasally with either SCH014-MA15 or SARS-MA15. Animals infected with SARS-MA15 lost weight rapidly and died within 4 days. Mice infected with SCH014-MA15 lost weight but did not die. When older (12 month) mice were used (these are more susceptible to SARS-MA15 infection), both viruses caused weight loss, but SARS-MA15 killed all the mice while SCH014-MA15 was less virulent (20% of mice died).

Second lesson learned: a human SARS-CoV with a bat glycoprotein can infect mice but is attenuated compared to a human, mouse adapted strain.

The next question asked was whether monoclonal antibodies (think ZMAPP, used in some Ebolavirus infected patients) against SARS-CoV could protect cells from infection with SCH014-MA15. The answer is no.

Third lesson learned: anti-SARS-CoV monoclonal antibodies do not protect from infection with SCH014-MA15.

Could an inactivated SARS-CoV vaccine protect mice from infection with SCH014-MA15?  An inactivated SARS-CoV vaccine provided no protection against infection SCH-014-MA15. When mice were first infected with a high dose of SCH014-MA15, there was some protection against challenge with the same virus, but protection did not last. And the side effects, weight loss and some death, would not be acceptable for a vaccine.

Fourth lesson learned: an inactivated SARS-CoV vaccine does not protect against infection with SCH014-MA15, and the recombinant virus itself is barely protective but not a safe vaccine.

In the final experiment of the paper, the SCH014 virus was recovered from an infectious DNA clone made from the genome sequence. This virus infected primary human airway epithelial cell cultures but not as well as did SARS-CoV Urbani. In mice SCH014 did not cause weight loss and it replicated to lower titers than SARS-CoV Urbani.

Fifth lesson learned: At least one circulating SARS-like bat CoV can infect human cells, but causes only mild disease in mice. Additional changes in the viral genome would likely be needed to cause a SARS-like epidemic.

Let’s now take a look at some of the public statements that have been made about this work.

Richard Ebright says that ‘The only impact of this work is the creation, in a lab, of a new, non-natural risk”. He could not be more wrong. For Ebright’s benefit, I submit my summary above of what we have learned from this work. Furthermore, I suggest that Ebright has not read the paper, or if he had, he has not put it in the context of the gaps in our knowledge of bat coronavirus potential to infect humans. This type of negative quote is easily picked up by the press, but it’s completely inaccurate.

Simon Wain-Hobson says that a novel virus was created that ‘grows remarkably well’ in human cells; ‘if the virus escaped, nobody could predict the trajectory’.

I do agree that we cannot predict what would happen if SCH014-MA15 were released into the human population. In my opinion the risk of release and spread of this virus in humans is very low. The attenuated virulence of the SCH014-MA15 virus in mice suggests (but does not prove) that the recombinant virus is not optimized for replication in mammals. Recall that the virus used to produce the recombinant, SARS-MA15 is mouse-adapted and may very well have lost some virulence for humans. In a broader sense, virologists have been manipulating viruses for years and none have gone on to cause an epidemic in humans. While there have been recent lapses in high-containment biological facilities, none have resulted in harm, and work has gone on for years in many other facilities without harm. I understand that none of these arguments tell us what will happen in the future, but these are the data that we have to calculate risk. Bottom line: the risk of these experiments is very low.

I think the statements by Ebright and Wain-Hobson are simply meant to scare the public and push us towards regulation of what they believe are ‘dangerous’ experiments. They are misleading because they ignore the substantial advances of the work. The experiments in this paper were well thought out, and the conclusions (listed above) are substantial. Creation of the recombinant virus SCH014-MA15 was needed to show that the spike glycoprotein could mediate entry into human cells. Only after that result was obtained did it make sense to recover the SCH014 bat virus. We now understand that at least one circulating bat SARS-like CoV can infect human cells and the mouse respiratory tract. More importantly, infection cannot be prevented with current SARS monoclonal antibodies or vaccines.

This information means that we should embark on a program to understand the different SARS-like spike glyocoproteins on bat CoVs, and try to develop therapeutics to prevent a possible second spillover into humans. This work will require further studies of the type reported in this paper.

My conclusion: these are low risk, high benefit experiments. You may disagree with my assessment of risk, but you cannot deny the benefits of this work. If you do, you simply haven’t read and understood the paper.

As you might imagine, the press has had a field day with this work. But many of these articles are misleading. For example, the headline of the Motherboard article touts “Ethical Questions Arise After Scientists Brew Super Powerful ‘SARS 2.0’ Virus”. As I pointed out above, both SCH014-MA15 and SCH104 are less virulent in mice than SARS-CoV, so this headline is completely wrong. An article in Sputnik International has the headline “Uncaging the Animal: Concerns Rise Over Scientists Tests on SARS 2.0” and the sub-headline is “‘SARS 2.0’ is closer than you might think as scientists are continuing medical tests that could create a whole new virus outbreak.” The article claims that the experiments are ‘science for the sake of science’. If the author had read the Nature article, he or she could not have reached that conclusion. Both articles feature scary quotations by Ebright and Wain-Hobson. The most egregious may be an article in the Daily Mail, which claims that “New SARS-like virus can jump directly from bats to humans without mutating, sparking fears of a future epidemic”. This statement is also wrong – there are no data in the paper which show that the virus can jump from bats to humans!

Perhaps at fault for much of this hyperbole is the press release on this work issued by the University of North Carolina, the home of the paper’s authors. The headline of the press release is: “New SARS-like virus can jump directly from bats to humans, no treatment available”. Exactly the same as the Daily Mail! Other errors in the press release emphasize that researchers need to work more closely with publicity departments to ensure that the correct message is conveyed to writers.

TWiV 360: From Southeastern Michigan

On episode #360 of the science show This Week in Virology, Vincent visits the University of Michigan where he and Kathy speak with Michael, Adam, and Akira about polyomaviruses, virus evolution, and virus assembly, on the occasion of naming the department of Microbiology & Immunology a Milestones in Microbiology site.

You can find TWiV #360 at Or you can watch the video below.

TWiV 355: Baby’s first virome

On episode #355 of the science show This Week in Virology, the TWiV team considers the effect of a Leishmaniavirus on the efficacy of drug treatment, and the human fecal virome and microbiome in twins during early infancy.

You can find TWiV #355 at

1977 H1N1 influenza virus is not relevant to the gain of function debate

The individuals who believe that certain types of gain-of-function experiments should not be done because they are too dangerous (including Lipsitch, Osterholm, Wain-Hobson,) cite the 1977 influenza virus H1N1 strain as an example of a laboratory accident that has led to a global epidemic. A new analysis shows that the reappearance of the 1997 H1N1 virus has little relevance to the gain-of-function debate.

Human influenza viruses of the H3N2 subtype were circulating in May of 1977 when H1N1 viruses were identified in China and then Russia. These viruses spread globally and continue to circulate to this day. The results of serological tests and genetic analysis indicated that these viruses were very similar to viruses of the same subtype which circulated in 1950 (I was in the Palese laboratory in 1977 when these finding emerged). Three hypotheses were suggested to explain the re-emergence of the H1N1 virus: a laboratory accident, deliberate release, or a vaccine trial.

Rozo and Gronvall have re-examined the available evidence for the origin of the 1977 H1N1 virus. While there is ample documentation of the extensive work done during the 1970s in the Soviet Union on biological weapons, there is no evidence that Biopreparat had attempted to weaponize influenza virus. The release of the 1977 H1N1 virus from a biological weapons program is therefore considered unlikely.

It is more likely that the 1977 H1N1 virus was released during testing of influenza virus vaccines. Many such trials were ongoing in the USSR and China during the 1960s-70s. C.M. Chu, a Chinese virologist, told Peter Palese that the H1N1 strain was in fact used in challenge studies of thousands of military recruits, an event which could have initiated the outbreak.

The hypothesis that the 1977 H1N1 virus accidentally escaped from a research laboratory is formally possible, but there are even less data to support this contention. Shortly after this virus emerged, WHO discounted the possibility of a laboratory accident, based on investigations of Soviet and Chinese laboratories. Furthermore, the H1N1 virus was isolated at nearly the same time in three distant areas of China, making release from a single laboratory unlikely.

It is of interest that with the onset of the gain-of-function debate, which began in 2011 with the adaptation of influenza H5N1 virus to aerosol transmission among ferrets, the ‘laboratory accident’ scenario for the emergence of the 1977 strain has been increasingly used as an example of why certain types of experiments are ‘too dangerous’ to be done (See graph, upper left). For example, Wain-Hobson says that ‘1977 H1N1 represented an accidental reintroduction of an old vaccine strain pre-1957, probably from a Russian research lab’. Furmanski writes that ‘The virus may have escaped from a lab attempting to prepare an attenuated H1N1 vaccine’. In the debate on gain-of-function experiments, the laboratory escape hypothesis is prominently featured in public presentations.

The use of an unproven hypothesis to support the view that some research is too dangerous to do is another example of how those opposed to gain-of-function research bend the truth to advance their position. I have previously explained how Lipsitch incorrectly represented the results of the H5N1 ferret transmission studies. We should not be surprised at this tactic. After all, Lipsitch originally called for a debate on the gain-of-function issue, then shortly thereafter declared that the moratorium should be permanent.

Rozo and Gronvall conclude that the use of the 1977 influenza epidemic as a cautionary tale is wrong, because it is more likely that it was the result of a vaccine trial and not a single laboratory accident:

While the events that led to the 1977 influenza epidemic cannot preclude a future consequential accident stemming from the laboratory, it remains likely that to this date, there has been no real-world example of a laboratory accident that has led to a global epidemic.

Virologists plan influenza H7N9 gain of function experiments

A group of virologists lead by Yoshihiro Kawaoka and Ron Fouchier have sent a letter to Nature and Science outlining the experiments they propose to carry out with influenza H7N9 virus.

Avian influenza H7N9 virus has caused over 130 human infections in China with 43 fatalities. The source of the virus is not known but is suspected to be wet market poultry. No human to human transmission have been detected, and the outbreak seems to be under control. According to the authors of the letter, the virus could re-emerge this winter, and therefore additional work is needed to assess the risk of human infection.

The research that the virologists propose involve gain-of-function experiments which provide the H7N9 virus with new properties. The isolation of avian influenza H5N1 viruses that can transmit by aerosol among ferrets is an example of a gain-of-function experiment.

The proposed gain-of-function experiments fall into five general categories:

  • Determine whether viruses with altered virulence, host range, or transmissibility have changes in antigenicity, or the ability of the virus to react with antibodies. The results of these studies would suggest whether, for example, acquisition of human to human transmissibility would have an impact on protection conferred by a vaccine produced with the current H7N9 virus strain.
  • Determine if the H7N9 virus could be adapted to mammals and whether it could produce reassortants with other influenza viruses. The results of this work would provide information on how likely it is that the H7N9 virus would become better adapted to infect humans.
  • Isolate mutants of H7N9 virus that are resistant to antiviral drugs. The purpose of these experiments is to identify how drug resistance arises (the mutations can then be monitored in clinical isolates), determine the stability of drug resistant mutants, and whether they confer other properties to the virus.
  • Determine the genetic changes that accompany selection of H7N9 viruses that can transmit by aerosol among mammals such as guinea pigs and ferrets. As I have written before, the point of these experiments, in my view, is not to simply identify specific changes that lead to aerosol transmission. Such work provides information on the mechanisms by which viruses can become adapted to aerosol transmission, still an elusive goal.
  • Identify changes in H7N9 virus that allow it to become more pathogenic. The results of these experiments provide information on the mechanism of increased pathogenicity and whether it is accompanied by other changes in properties of the virus.

I believe that the proposed gain-of-function experiments are all worth doing. I do not share the concerns of others about the potential dangers associated with gain-of-function experiments: for example the possibility that a virus selected for higher virulence could escape the laboratory and cause a lethal pandemic. Gain-of-function is almost always accompanied by a loss-of-function. For example, the H5N1 viruses that gained the ability to transmit by aerosol among ferrets lost their virulence by this route of infection. When these experiments are done under the proper containment, the likelihood that accidents will happen is extremely small.

All the proposed experiments that would use US funds will have to be reviewed and approved by the Department of Health and Human Services:

The HHS review will consider the acceptability of these experiments in light of potential scientific and public-health benefits as well as biosafety and biosecurity risks, and will identify any additional risk-mitigation measures needed.

While I understand that the authors wish to promote a dialogue on laboratory safety and dual-use research, I question the ultimate value of the communication. Because the letter has been published in two scientific journals, I assume that the target audience of the letter is the scientific community. However, the letter will clearly have coverage in the popular press and I am certain that it will be misunderstood by the general public. I can see the headlines now: “Scientists inform the public that they will continue to make deadly flu viruses”. The controversy about the H5N1 influenza virus transmission studies in ferrets all began with a discussion of the results before the scientific papers had been published. I wonder if the publication of these letters will spark another controversy about gain-of-function research.

In my view, science is best served by the traditional process known to be highly productive: a grant is written to secure funding for proposes experiments, the grant proposal is subject to scientific review by peers, and based on the review the work may or may not be supported. The experiments are done and the results are published. I do not understand why it is necessary to trigger outrage and debate by announcing the intent to do certain types of experiments.

I am curious to know what the many readers of virology blog – scientists and non-scientists – feel about the publication of this letter. Please use the comment field below to express your views on this topic.