As the 2014 Ebola outbreak claimed lives in West Africa and threatened to spread beyond its region of origin, many Americans were surprised to learn that biopharmaceutical companies already had experimental treatments and vaccines in preparation. None had received regulatory clearance, and work on some had been suspended or delayed for lack of funding. The epidemic prompted governments, NGOs, companies, and regulators to redouble development efforts and expedite clinical testing. The outbreak has now wound down, but Ebola remains a threat and the search for medicines continues. In this article, Daniel Levine reviews the history of Ebola research. He surveys progress and problems in the development of drugs and vaccines against the virus, and looks ahead to the future.

Through the summer of 2003, virologists Thomas Geisbert, of the University of Texas Medical Branch in Galveston, and the US Army Medical Research Institute of Infectious Diseases (USAMRIID) at Fort Detrick in Maryland, and Heinz Feldmann, of the Public Health Agency of Canada (PHAC) in Winnipeg, Manitoba, worked collaboratively to discover how the Ebola virus infects cells and wreaks life-threatening havoc in non-human primate hosts.

Thomas Geisbert (Bryan Schutmaat / TIME)

They worked in BSL-4 (biosafety level 4) laboratories, facilities providing the highest level of containment security. BSL-4 labs integrate multiple redundant isolation, decontamination, and safety systems. They are enormously expensive to operate and maintain, and enormously cumbersome to work in. There are only fifteen BSL-4 labs in the United States (Fort Detrick has four). The National Microbiology Laboratory in Winnipeg is Canada’s sole level 4 facility.

To investigate mechanisms of Ebola replication without causing disease or endangering laboratory personnel, Geisbert and Feldmann used recombinant DNA techniques to replace an outer coat protein of the vesicular stomatitis virus (VSV) — a member of the Rhabdoviridae family of viruses that is mostly harmless to primates — with a non-pathogenic surface glycoprotein from the Ebola virus.

The Ebola glycoprotein plays a crucial role in viral infections — it attaches to, fuses with, and opens up host cells, allowing the virus’ RNA to enter. Use of the reengineered VSVs permitted Geisbert and Feldmann to show how Ebola invades host organisms and commandeers cells for viral reproduction. The researchers also recognized the potential of the invention as a vaccine. Exposure to the glycoprotein, they hypothesized, could generate a protective immune response.

To test the idea, they inoculated eight healthy adult cynomolgus macaques with the modified virus. None became ill. They waited twenty-eight days and then exposed the animals to live Ebola virus. The experimental vaccine protected them — there were no fevers, no symptoms of any kind. Two untreated macaques were included in the experiment as controls. Both perished.

The researchers reported the stunning result in the July 2005 issue of Nature Medicine. They expected a pharmaceutical company to snap up their work and develop it, but nothing happened. For most of the next decade, the vaccine languished on a shelf, ignored and neglected, like many other experimental Ebola vaccines and therapies.

When asked in July 2014 about the prospects for developing viable drugs or vaccines for Ebola, Geisbert said, “They already exist.” But they’re not yet available for use. The reasons are partly scientific — safety and efficacy need first to be established in clinical trials — but mostly economic and political.

Historically, Ebola outbreaks have occurred in isolated rural populations in some of the world’s poorest countries, for only brief periods because infections progress so rapidly. The epidemics have quickly burned themselves out. Although mortality rates have been high, death tolls have been relatively low. Before the most recent outbreak in 2014–2015, governments had little incentive to invest in Ebola treatments and vaccines.

The worst outbreak

On March 23, 2014, the African Regional Office of the World Health Organization reported the presence of Ebola in Guinea, in three towns near the West African country’s southern border. It spread quickly to Liberia, then Sierra Leone and Nigeria, but it wasn’t until August at a press conference in Geneva that WHO Director General Margaret Chan declared an international public health emergency: “This is the largest, most severe and most complex outbreak in the nearly four-decade history of this disease.”

At the time, 1,711 people had contracted the disease and 932 had died. By mid-April 2015, the death toll had climbed to more than 10,000, far surpassing the cumulative total of 1,600 deaths that had occurred in all previous outbreaks since the first recorded episode in 1976.

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The prior episodes — seventeen in all — had been localized, short-lived, and limited to fewer than 400 infections, so when the spread of disease slowed momentarily in Liberia, Guinea, and Sierra Leone late in the spring of 2014, African health officials began to relax. They were wholly unprepared for what happened next: instead of diminishing and disappearing, the virus moved suddenly into major population centers, including Monrovia, Liberia, a city of more than 500,000, and Conakry, Guinea and Freetown, Sierra Leone, each with more than 1 million residents.

As the outbreak intensified, epidemiological monitoring was hindered by weak healthcare infrastructures. Health workers were few and inexperienced with Ebola. Inadequate precautions for patient handling (the virus is contracted through close contact) elevated infection rates among family members and caregivers. West African customs also helped to fuel the spread of disease — burial ceremonies typically involved putting hands on the dead. Compounding these problems was the fact that years of political instability and civil war in the region had left citizens distrustful of government and public health efforts.

Four months after initial reports of Ebola infections, the international community took notice. Health officials were alarmed. They worried that they might see a massive surge in infections. Several countries sent protective gear and lab equipment to help quell the outbreak in West Africa, but even with assistance, the governments of Guinea, Sierra Leone, and Liberia were unable to catch up with the virus. When Tom Frieden, director of the US Centers for Disease Control and Prevention, visited the region in late August, he described what he saw as “a scene out of Dante.”

Images from the outbreak in Guinea (Marie-Agnës Heine and Jose Rovira Vilaplana / WHO)

By that time, the virus had reached Lagos, Nigeria with a population of more than 5 million. Public health officials in Europe and North America expressed fears that infected travelers would carry it out of Africa. On September 15, President Barack Obama announced that the United States would dispatch 3,000 troops and additional personnel from the CDC, the Department of Defense, and the Army Corps of Engineers to Monrovia, to establish a command and control center and coordinate an international effort to contain the outbreak.

The first case of Ebola in the United State was confirmed soon after, on September 24, in Dallas, Texas. The patient was initially misdiagnosed, and the public’s worst fears were confirmed — infected persons could enter the country undetected and spread disease for several days before exhibiting symptoms (and in this instance, after). Officials at Customs and Border Protection (CPB) and the Centers for Disease Control and Prevention (CDC) reacted quickly. They dispatched teams to begin screening passengers arriving from Africa at international airports.

Various federal agencies began contacting biotech companies to request access to shelved experimental drugs. Many had been developed with government funding, not because of any perceived threat of an epidemic spreading from Africa to the United States, but rather because the National Security Agency had reckoned that terrorists could use the virus as a biological weapon.

The threat of bioterror

Following the 9/11 attacks on the World Trade Center and the Pentagon, and the delivery one week later of anthrax spores to media companies and Congressional offices, Ebola became one of several infectious agents placed on the US government’s list of threats requiring countermeasures.

A little more than a year later, on January 28, 2003, President George W. Bush gave his annual State of the Union address. He identified bioterror as a serious risk to national security and announced plans to mobilize biomedical scientists and private sector research and development capabilities for homeland defense.

On February 3, the White House released an outline of the president’s proposed budget for 2004. It included $890 million apportioned to the Department of Health and Human Services (HHS) and the newly formed Department of Homeland Security (DHS) to launch Project BioShield and fund the production of drugs and vaccines against smallpox, anthrax, botulinum toxin, plague, and Ebola. Congress subsequently approved expenditures of nearly $5.6 billion to sustain the project for ten years.

In January 2004, the Project BioShield Act went into force with provisions designed to expedite scientific peer reviews, accelerate the US Food and Drug Administration’s approval process for medical countermeasures to bioterror threats, and provide the National Institutes of Health with contracting flexibility and infrastructure improvements. The National Institute of Allergy and Infectious Disease (NIAID) played a central role — it was charged with awarding biodefense grants and contracts. In 2001, NIAID budget for biodefense research was $200 million. Between 2004 and 2012, annual spending averaged $1.6 billion.

In 2005, Congress passed and President Bush signed into law the Biodefense and Pandemic Vaccine and Drug Development Act. The Act created a new agency within the Department of Health and Human Services (HHS) — the Biomedical Advanced Research and Development Authority (BARDA) — to accelerate the development of drugs and vaccines as countermeasures against pandemics and the use of infectious agents in biological warfare. BARDA investments involved multiple agencies and multiple disease and drug and vaccine research programs.

Between 9/11 and the end of 2014, the federal government poured more than $78 billion into efforts by eleven federal departments and agencies to address bioterror threats. Only a small percentage of available funds went to Ebola programs — far more money went to research on smallpox, anthrax, and plague — but these various actions and programs positioned the federal government as a guaranteed buyer of experimental drugs and vaccines. Without the federal commitment to stockpile, there would be no market, and pharmaceutical companies would have no incentive to dedicate resources to development projects.

Small biotech companies played crucial roles in the Ebola biodefense effort. They invented therapies and vaccines and sought assistance from government partners in order to ready them for the clinic. Crucell, for example, a Dutch firm (since acquired by Johnson & Johnson) was awarded an NIH grant for vaccine research and development, as were Okairos, a Swiss/Italian company (acquired by GlaxoSmithKline), and Profectus of Baltimore, Maryland. Mapp Biopharmaceutical of San Diego received NIH funding, and BioCryst of Birmingham, Alabama and Tekmira of Burnaby, British Columbia secured support from USAMRIID and DOD for therapeutics development.

USAMRIID’s Geisbert expresses his admiration and appreciation: “Little companies like Mapp, Tekmira, and Profectus — these guys have been awesome. They’re the ones that kept a lot of this alive. For big companies, the profit margins weren’t there.” Geisbert credits the National Institutes of Health, as well: “I can tell you if we didn’t have the Partnerships for Biodefense program from the National Institutes of Health, some of this stuff would have fallen by the wayside.”

After the 2008 financial crisis, monies from the economic stimulus insulated Ebola projects for a short period, but pressure on budgets during the ensuing recession eventually forced deep research cutbacks. In 2010, NIAID distributed $142 million for Ebola research. By 2013, the figure had fallen to $96 million. NIH funding for Ebola vaccine development fell from $37 million in 2010 to $18 million in 2014.

On September 10, 2014, NIH Director Francis Collins went to Capitol Hill to testify before a House Energy and Commerce Subcommittee on Health and Medicine. He spoke about a vaccine that NIAID had been working on since 2001 in partnership with GlaxoSmithKline and the Wellcome Trust. It had worked well in animals, but had not yet made it into Phase 1 clinical trials in human beings (it has since been fast-tracked into Phase 2/3 trials). Collins suggested to the subcommittee that had the project been adequately funded, it would have been ready for distribution, many lives could have been saved, and Liberia, Guinea, and Sierra Leone might have been spared devastating economic damage.

(Cynthia Goldsmith / CDC)

Know your enemy: Ebola

Ebola belongs to the Filovirus family, which includes the Marburg virus, another African threat that produces hemorrhagic fever. There are five known kinds of Ebola. The most recent outbreak involved the drifted Makona variant of the Zaire strain. When viewed under an electron microscope, the virus appears as a single, tangled filament. It is transmitted through direct contact with blood, secretions, and other bodily fluids of infected people. It can take up to 21 days after infection for symptoms (fever, headache, fatigue, muscle pain, and sore throat) that are often mistaken for the onset of other ailments to manifest.

Ebola infections are vicious. The illness progresses as the virus takes over and destroys cells in the process of reproducing itself. Late stage symptoms include vomiting, diarrhea, severe dehydration, and internal and external bleeding. By the end stage, those infected excrete as much as ten liters of virus-infected fluids per day, putting caregivers at greater risk of infection. Death usually results from shock induced by fluid loss. Mortality rates in previous outbreaks have reached as high as 90 percent, although generally the figure is closer to 50 percent.

Hurry up and wait

The experience of Sarepta Therapeutics illustrates some of the pitfalls of dependence on government funding. Sarepta is a Cambridge, Massachusetts-based antisense drug company best known for its work on a treatment for Duchenne muscular dystrophy. It was established in Corvallis, Oregon, in 1980, as AntiVirals, Inc., to combat infectious diseases with Morpholino antisense oligos, short nucleic acid molecules designed to disrupt disease mechanisms by binding bacterial mRNA or viral nucleic acids.

By the early 2000s, the company had moved to Bothell, Washington and changed its name to AVI Biopharma. It was using genomics and proteomics screening to identify and characterize drug targets — defective disease-associated genes or proteins critical to the reproduction or virulence of bacterial and viral pathogens. Once targets were characterized, the firm had the capability to quickly synthesize interfering Morpholino oligos.

AVI’s work with Ebola began in 2004 when a researcher at USAMRIID at Fort Detrick accidently stuck herself with an Ebola-contaminated needle. A colleague at the facility had learned about AVI’s special expertise in rapid production of therapies against select molecular targets in infectious pathogens. He called the company to inquire about a drug for Ebola. The request came on a Thursday; a drug was delivered the following Tuesday.

The US Food and Drug Administration (FDA) approved use of the experimental treatment, provided that the patient tested positive for Ebola. The blood test was negative, and the drug was never administered, but with a potential treatment already in hand, the company decided to move ahead with a development project. It began testing the oligo in animals.

Eventually, Sarepta’s quick turnaround capabilities attracted interest from the Department of Defense, which put the company to the test in series of a rapid response exercises. The firm performed well and the DOD followed up. In July 2010, the company was awarded a $291 million Chemical and Biological Defense Program contract to develop therapies for Ebola and Marburg, a related Filovirus that also causes hemorrhagic fever.

But a little more than two years later, when the economic downturn forced government agencies to pare spending, the DOD notified Sarepta, now located in Cambridge, Massachusetts, that it was terminating the Ebola portion of the contract. The company had completed a Phase 1 clinical trial in healthy adult volunteers. The trial had demonstrated safety and the drug had earned a fast track designation from the FDA.

Chris Garabedian

Says Chris Garabedian, then CEO of Sarepta: “The division had to cut one of its advanced development projects. The drug was safe. It showed therapeutic activity. I think we probably had more extensive research experience with non-human primates in BSL4 labs than any of the other companies developing Ebola drugs, but despite all of that, funding for our Ebola program cut in 2012.”

It was frustrating for Garabedian, who believed that the company’s technology could combat Ebola and a broad range of serious infectious diseases with rapid responses to sudden outbreaks. But in the absence of government funding, the drug had to wait. There was no private sector interest in the project.

“Unfortunately,” says Garabedian, “I don’t think any biotech out there is going to take investor dollars and put them into a program that doesn’t have a clear pathway to generate revenues and profits. There isn’t much precedent for investing in drug development on a proprietary basis without a clear procurement contract for stockpiling or an ongoing thriving market for these diseases. I think the recent Ebola outbreak has demonstrated this.”


Many Ebola development projects stalled after 2010, but when the virus came out of hiding in West Africa in 2014, the biopharmaceutical industry and government partners had more than a dozen experimental drugs and vaccines in preclinical or early stage clinical testing. The pipeline included potential treatments that large pharmaceutical companies had obtained through the acquisition of smaller biotech companies.

As the Ebola death toll began spiraling upwards in the summer months, government agencies and other R&D funders, including the Wellcome Trust and the World Health Organization (WHO), urged large pharmaceutical companies to take over and hasten the advance of candidate drugs and vaccines into clinical trials. A positive response led to three vaccines moving from testing in animals to late-stage human efficacy trials in less than a year.

In August 2014, WHO declared the Ebola outbreak a global public health emergency, and in September, the CEOs of three drugmakers — Andrew Witty of GlaxoSmithKline, Alex Gorsky of Johnson & Johnson, and Kenneth Frazier of Merck & Company — reportedly met and agreed to proceed independently with vaccine projects to increase the chances that one might be successful.

GSK had originally planned to begin clinical testing of an Ebola vaccine in March 2015, but quickly moved its timetable to September 2014, thanks to backing from an international consortium that included co-development work with the NIAID and funding from the Wellcome Trust, the UK Medical Research Council, and the UK Department for International Development.

The funding allowed GSK to manufacture 10,000 doses of the vaccine, in addition to trial doses, to be made immediately available to the WHO for an emergency immunization program in high-risk communities should initial US, UK, and African trials prove successful. Early results released at the end of January 2015 showed an induced immune response. The experimental NIAID/GSK vaccine, originally developed by Okairos, is based on an attenuated strain of a chimpanzee cold virus to deliver a glycoprotein from the Ebola Zaire virus.

J&J’s multivalent combination vaccine is intended to be effective against all forms of Ebola, as well as Marburg. It is based on technologies developed by the Danish biotech Bavarian Nordic and the Dutch biotech Crucell, which was acquired by J&J’s Janssen Pharmaceuticals in 2010. In September 2014, J&J said it would fast track development of the vaccine in collaboration with NIH.

Earlier studies showed that the combination vaccine provided complete protection of vaccinated macaques against disease and death after exposure to a highly virulent wild type Ebola Zaire strain. Clinical studies in healthy humans began in early 2015, with the first volunteers receiving the first of two doses to prime the immune system. J&J announced at that time that it had produced a sufficient amount of vaccine for a large late-stage trial to commence in May 2015, and had the capacity to manufacture up to five million doses by the end of the year.

Merck took just one month to identify and license an experimental Ebola vaccine being developed by NewLink Genetics. Merck paid NewLink $30 million upfront in November 2014 and an additional $20 million on the initiation of late-stage clinical trials that began in February 2015.

NewLink originally licensed the vaccine from the Public Health Agency of Canada (PHAC). It was based on the work of Geisbert at the USAMRIID and Heinz Feldmann at PHAC with vesicular stomatitis virus (VSV). In March, the NIAID and Liberian researchers launched late-stage trials of the GSK and Merck vaccine candidates. In April, Merck began enrolling frontline health workers in Sierra Leone as volunteers to test the safety and efficacy of its vaccine.

The Merck/Newlink vaccine is not the only one of its kind. Profectus Biosciences, a Baltimore-based biotech, spun out of Wyeth, is also pursuing a recombinant VSV vaccine based on Geisbert and Feldmann’s work. Several years ago, the two researchers approached Profectus looking for help in attenuating the virus so it would be safer for use in humans (VSV sometimes causes mild flu symptoms). For several years, company researchers had been working on attenuating VSV for use in other vaccines.

In the absence of government funding, Profectus decided to absorb the cost of animal studies. Then, armed with encouraging results that showed the vaccine had conferred protection against a lethal challenge of the Ebola virus in rhesus macaques, the company began sending grant applications to various government agencies including BARDA, DOD, and NIH.

“We’d gone to Washington twice a year for three years in a row and said, “Here are these really good results,” says John Eldridge, chief scientific officer for Profectus. “They’d thank us and say, “It looks good. It’s worthy of being developed, but Ebola and Marburg outbreaks are rare and small. It was on their threat list, but not high on their threat list and it didn’t make the cut for any kind of funding.”

Profectus managed to procure a $5.4 million grant in May 2012 from the NIH to develop a trivalent vaccine against Filoviruses including all major strains of the Ebola and Marburg viruses. But interest in Profectus’ research grew after the 2014 outbreak. The company attracted more than $40 million in combined funding from NIH, BARDA, and the DOD in recent months.

Profectus is pursuing both a monovalent vaccine for the Zaire strain of Ebola, expected to enter the clinic by June of 2015, and a trivalent vaccine covering all Ebola strains, which is expected to be ready for testing by September of 2015. Results of a study, published in the April 2015 issue of Nature showed that one dose of the trivalent rVSV vaccine protected monkeys against the Makona variant, the cause of the 2014 outbreak, without side effects.

One advantage VSV vaccines have over some of the others in development is that they confer protection on the first dose. This makes them well suited for treating healthcare workers who may face sudden deployment, or for creating a ring of immunity around an outbreak, particularly in an area where it may be difficult to get patients to return for a booster shot after an initial vaccination. Eldridge says a second shot will likely be necessary for immunity that lasts for years. Nevertheless, he says, the protection on a single dose provides a great field advantage in the event of an outbreak.

Eldridge wants to underscore the essential contributions of biotech companies to global health in the early twenty-first century. Governments funded the work, he says, and large pharmaceutical companies have used their clinical, manufacturing, and distribution muscle to deliver products, but in his view, biotech firms were the source of the innovative response to the recent Ebola outbreak:

“Small companies like Profectus are that engines that take useful science out of academic environments and advances it forward, into product development and into the clinic. We spend time working on applications and indications that are not big enough for the large pharmaceutical companies to address.”

A clinical quandary

During the final week of January 2015, the pace of new Ebola infections in Liberia, Guinea, and Sierra Leone, the three countries most deeply affected, slowed to fewer than 100 new cases, the lowest rate in seven months. It raised hopes that the outbreak was winding down. The WHO announced that the focus of its emergency response would shift from slowing transmission of the virus to snuffing it out.

The decrease in new cases was wonderful news, but it jeopardized plans to conduct clinical trials of new vaccines and therapeutics. The big pharmaceutical companies were able to accelerate the pace of Ebola vaccine trials, but the endpoint in vaccine testing is an immune response. Thousands have been vaccinated but if too few become exposed to the virus, there will be no way to know whether it confers immunity.

Drug testing is more complicated, since drugs must be administered to infected patients in isolation. Years ago, the FDA recognized that field trials for Ebola drugs and vaccines would likely be impractical. The disease progresses and kills rapidly, and outbreaks had burned out quickly in remote areas. The agency outlined a plan to use appropriate animal models as surrogates, but the unexpected size and duration of the West African outbreak and its presence in cities created an opening for clinical testing.

In February 2015, Mapp Biopharmaceuticals announced that it had manufactured enough of its monoclonal antibody cocktail, called Zmapp, to begin trial dosing. The drug must be refrigerated and patients must be infused, which makes the project difficult logistically. Investigators had expected to be hampered by poor infrastructure in the affected region and by difficulties in monitoring patients and assuring compliance, but the greater concern now is enrollment — the population of infected patients is disappearing.

Four experimental drugs were administered to patients during the recent outbreak, under special dispensation from regulators for compassionate use: Zmapp, Tekmira’s RNAi therapeutic, TKM-Ebola, Toyoma Chemical’s RNA polymerase inhibitor, favipiravir, and Chimerix’s broad spectrum antiviral, brincidofovir. They were administered on a limited basis, in combination with other therapies, to patients with advanced symptoms. The conditions made it impossible to assess safety and efficacy.

Chimerix’s brincidofovir was the most advanced Ebola drug candidate, but the company elected to discontinue testing in January. It was a long shot to begin with — a DNA polymerase inhibitor against an RNA virus — but there were indications that it could have an effect. The compound halted the replication of Ebola in cell culture experiments. In any event, as the outbreak began winding down, the challenge of enrolling enough trial participants was already becoming a serious obstacle. Infections are dwindling and it appears that Ebola may slip away before investigators can record enough data to tell whether experimental drugs and vaccines can defeat it.

Dangers ahead

As a weapon of bioterror, Ebola has deficiencies. It tends to have lower transmission rates and smaller “hot zones” than many other pathogens — influenzas, for example — because it is so virulent and generally not transmitted through the air. As a consequence, government officials setting priorities for biodefense initiatives in the post-9/11 era ranked it as a lesser threat, an unlikely weapon of choice.

George Poste

Such negligence could be a general problem. There are almost certainly other deadly zoonotic diseases lying in unknown reservoirs, lurking in animal hosts, waiting to jump across species to trigger outbreaks in human beings without advance warning. George Poste, director of the Complex Adaptive Systems Initiative at Arizona State University, says there is a tendency to become complacent about such threats — out of sight, out of mind: “It’s something we need to be much more mindful of. There’s a frenzy of funding at the present time, but when it wanes, what will be the incentive for vaccine development?”

Instead of viewing the recent Ebola outbreak as an isolated incident, it should be understood as part of a broader picture: infectious diseases emerging on a panoramic landscape across Africa, the Middle East, Southeast Asia, and other regions as urbanization, growing population density, climate change, desertification of lands, increased demand for protein-rich foods, and the intensification of agriculture extend humankind’s encroachment on remote lands and increase the frequency of encounters with zoonosis.

The last thirty year have seen a host of new outbreaks around the world: HIV, SARS, MERS, avian flus, swine flus, and an ongoing fight to contain Chikungunya, which recently spread from the Caribbean into the United States. The effects, Poste says, are made worse when outbreaks occur in areas with poor public health infrastructures and inadequate means of tracking of infections.

It is easy to slip into complacency once an outbreak is contained, but the reality in a densely networked, shrinking world is that events posing grave threats to health and human welfare will continue to occur with increasing frequency. Poste believes that effective adaptive responses will require renewed attention to global public health, monitoring and detection, and economic incentives to engage industry:

“It all comes back to surveillance, creation of markets, and industry mobilization. You can have the smartest basic research you like, but if you can’t get it translated, it’s of no value. There must be incentives, whether for new antibiotics, new vaccines, or new diagnostics. And it must be industry that delivers them, because only industry has the necessary competencies.”

— Daniel S. Levine

Header image credit Centers for Disease Control

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