Measles: Causes, Symptoms, Diagnosis, Treatment & Prevention

Ebola: How A Vaccine Turned A Terrifying Virus Into A Preventable Disease

The Ebola virus devastated west Africa in 2014, claiming over 11,000 lives in Sierra Leone, Liberia and Guinea.

It was the largest Ebola outbreak since the virus had first been discovered in the Democratic Republic of Congo in 1976.

Ebola is a terrifying virus which, if left untreated, causes bleeding inside the body and through the eyes, nose, mouth and rectum.

Case fatality rates have varied from 25% to 90% in past outbreaks, depending on circumstances and the response.

The 2014 outbreak in west Africa exposed a critical gap in global preparedness for infectious diseases: the absence of effective vaccines.

There were no drugs or vaccines approved to treat or prevent Ebola or ready to enter into clinical trials at the outset of the epidemic. Therefore, many felt it was ethically necessary to conduct such research as quickly and safely as possible.

As a biologist and epidemiologist, I travelled to Guinea amid the chaos to coordinate the laboratory activities of the rVSV-ZEBOV Ebola vaccine trials.

Almost 10,000 participants were enrolled in trials to make sure the drug was safe and effective to use. The trials would last two years and involved more than 500 scientists and healthcare workers.

My five-year-old daughter, Ashanti, spoke words that strengthened my resolve: "People need you to support them. If you don't go, who will?"

Her encouragement fuelled me as I led the trial's laboratory operations, navigating immense logistical and emotional challenges.

We had to set up a full laboratory in a week, to process thousands of samples. Delivering the vaccine required ultra cold freezers (minus 80°C); none were available in the country.

We had to address vaccine hesitancy among the population of Guinea, including the medical and academic community.

Of course there was also fear of getting infected by a disease that was a virtual death sentence.

First line workers and individuals in close contact with confirmed Ebola cases were vaccinated with rVSV-ZEBOV. This created a protective "ring" around the infected.

As a field coordinator, I witnessed firsthand the challenges of conducting research into the safety of the vaccine in the middle of an outbreak.

Collaboration between the World Health Organization, Médecins Sans Frontières, the medical research centre Epicentre and local health authorities proved pivotal.

Volunteers in protective suits bury the body of an Ebola victim in Waterloo, 30km southeast of Freetown, in October 2014. Getty Images

These efforts also underscored the importance of adaptable, rapid-response research during health crises.

On 18 August 2015 the preliminary results of the trial were announced. They marked a turning point in the fight against Ebola. The vaccine's near-perfect efficacy offered a rare moment of hope.

Today Sierra Leone is embarking on a nationwide campaign with the rVSV-ZEBOV vaccine, trademarked as Ervebo.

The campaign will target 20,000 frontline workers in 16 districts. These include healthcare workers, traditional healers, community health and social workers, laboratory personnel, motorcycle taxi drivers and security forces. Anybody who will be involved in any response to future outbreaks.

How does Ervebo work?

The Ervebo vaccine, developed by Merck, is a single-dose vaccine. It works by using a modified virus to produce antibodies against Ebola, equipping the immune system to recognise and neutralise the virus upon exposure.

Clinical trials have shown its efficacy exceeds 95% in preventing infection from the Zaire Ebola virus strain, the deadliest variant.

The vaccine was deployed during the 2018-2020 Ebola epidemic in the Democratic Republic of Congo under emergency use authorisation.

This allows a medical product to be used without being authorised by the relevant drug agencies, such the Food and Drug Administration in the United States, the European Medicines Agency and the African Medicines Agency.

It was also used in Burundi, Uganda, South Sudan and Rwanda in preventive vaccination campaigns to protect healthcare and frontline workers.

A specialised Ebola inhumation team carry the body of an Ebola victim in October 2014 in Mananeh, Sierra Leone. Getty Images

Ervebo is now a cornerstone in the fight against Ebola, particularly in controlling outbreaks caused by the Zaire strain.

However, its success depends on ensuring equitable access and strengthening healthcare systems.

What are the challenges?

Challenges do persist, including limited vaccine supply, logistical hurdles in remote regions, and vaccine hesitancy fuelled by misinformation.

Addressing these obstacles requires coordinated efforts between governments, health organisations and communities.

Additionally, establishing local vaccine manufacturing in Africa should be a long-term goal, giving affected countries greater control over supply and distribution.

Could the vaccine bring an end to Ebola?

While Ervebo is a monumental achievement, it cannot end Ebola on its own.

The virus's ability to persist in animal reservoirs such as bats and to then be transmitted to humans means that vaccination must be part of a broader strategy.

Integrating vaccination, surveillance, outbreak response and community engagement is essential for achieving long-term control.

Ervebo's success provides a model for addressing other infectious disease outbreaks, like mpox. Clinical trials during the mpox outbreak could potentially lead to new and effective vaccines.

Emerging Infectious Diseases

Influenza (or flu) is an example of an emerging disease that is due to both natural and human factors. Influenza virus is infamous for its ability to change its genetic information. Large changes in the influenza virus can cause pandemics because the human immune system is not prepared to recognize and defend against the new variant. The chances of large genetic changes occurring and being passed into humans are increased when humans coexist in close proximity with agricultural animals such as chickens, ducks, and pigs. These animals are natural hosts of influenza virus and can act as mixing vessels to create novel versions of influenza that have not existed previously. Avian H5N1 influenza (or bird flu), which emerged more than a decade ago, has been limited to relatively rare instances of infection in humans who came into direct contact with diseased birds. The H5N1 virus is very deadly (more than half the cases have been fatal), but it has not acquired the ability to pass efficiently between humans. In contrast, the 2009 H1N1 influenza, which passed into humans from swine (pigs), transmitted easily from person to person and traveled quickly around the world as a result of human activity, particularly air travel. Fortunately, it was much less deadly than the H5N1 virus. Emergence of an influenza virus that is as deadly as the avian H5N1 virus and is spread between people as easily as the swine H1N1 virus would be a very serious threat to human health.

The case of the coronaviruses SARS-CoV, MERS-CoV, and SARS-CoV-2 (which cause the diseases SARS, MERS, and COVID-19 respectively), represents instances of how viruses can move from animals into humans, acquire the ability to spread from person to person and then, with great speed, reach around the globe as a result of air travel. These three viruses, which all cause severe respiratory illnesses and can be fatal, originated in bats and spilled over into the human population through close contact with an intermediate animal. SARS emerged in China in 2002, MERS in the Arabian Peninsula in 2015, and COVID-19 in Wuhan, China at the end of 2019. For SARS, an unprecedented global response halted the spread of the causative virus but not before 8000 people had been infected and 800 died. MERS has been largely contained but not before spreading to 27 countries and causing 2,500 infections and close to 900 deaths. The outcome of SARS-CoV-2, however, has been vastly more devastating. Aided by delayed and uncoordinated global responses, insufficient containment measures, and the fact that infected people can transmit the virus even in the absence of symptoms, the virus raged beyond the ability to control its spread and resulted in a worldwide pandemic that has lasted over a year and caused around three million deaths globally. 

An example of an emerging infectious disease that can be attributed to human practices is HIV. It is thought that humans were first infected with HIV through close contact with chimpanzees, perhaps through bushmeat hunting, in isolated regions of Africa. It is likely that HIV then spread from rural regions into cities and then internationally through air travel. Further factors in human behavior, such as intravenous drug use, sexual transmission, and transfer of blood products before the disease was recognized, aided the rapid and extensive spread of HIV.

One instance of a tropical disease that has spread recently into new areas that may be due, at least in part, to changing climate is chikungunya. Chikungunya disease is caused by the chikungunya virus, a relative of the virus that causes Dengue fever. It is transmitted by the tiger mosquito, and in the past was confined to tropical regions around the Indian Ocean. In late summer of 2007, more than 100 residents of the town of Ravenna, Italy suffered from a mysterious disease that produced fever, exhaustion, and severe bone pain. The outbreak was eventually shown to be caused by chikungunya virus. By 2014, chikungunya outbreaks have been reported in countries in Europe, Asia, Africa, and the Americas (Caribbean and Central and South America). The virus arrived in the United States in the summer of 2014, although thus far local transmission of chikungunya virus has been limited to Florida and Texas. Although chikungunya virus does not usually cause a fatal disease, it serves as a warning that other, more devastating tropical diseases could follow. In fact, a more serious threat is the recently emergent Zika virus in the Americas which is associated with a birth defect known as microcephaly.

Finally, the Ebola virus epidemic that emerged in 2014 in West Africa illustrates how a virus that previously affected only small groups of people, perhaps a few hundred, can sweep rapidly through an area to affect tens of thousands, and become extremely difficult to contain. A combination of factors including high population densities, increased travel, closer contact with wild animals, weak health care systems, and a slow response led to the worst outbreak of Ebola the world has ever seen.

Review Reveals 22 Viruses, Some With Pandemic Potential, In Semen

A new systematic review of 373 studies reveals the detection of 22 viruses in human semen following acute infection, including pathogens with pandemic potential. The study was published yesterday in The Lancet Microbe, and shows that only 9 of the 22 viruses had evidence of sexual transmission.

The persistence of viruses in semen has far-reaching implications for ongoing disease transmission, embryonic development and fertility, and the development of drugs and vaccines, the authors said. Infectious semen has also contributed to recent outbreaks of Zika virus disease, Ebola virus disease, and mpox.

In this review, the authors examined evidence of viruses in semen as well as viral persistence, or how many days after the onset of illnesses that viruses are viable in semen. 

In addition to the 22 viruses present in semen following acute infection, 3 others—Crimean-Congo hemorrhagic fever virus, hantavirus causing hemorrhagic fever with renal syndrome, and Heartland virus—were detected in other parts of the human male reproductive tract, but not in semen. Hepatitis A virus and vaccinia virus showed evidence for sexual transmission but no evidence for detection in the semen or elsewhere in the male reproductive tract.

Ebola had longest persistence 

Ebola virus had the longest viral persistence, detected 988 days after discharge from an Ebola treatment unit and 965 days after onset of illness, in separate studies, the authors said. 

The maximum detection of Zika virus in semen was 941 days after onset of illness, but the median persistence was 57 days after onset of illness. The shortest duration was 8 days after onset of illness for Kyasanur Forest disease. Maximal detection time for other viruses was 21 days for yellow fever virus, 22 days for West Nile virus, and 37 days for dengue virus.

We found considerable variability between individuals with regard to the duration of persistence of virus in the semen.

"We found considerable variability between individuals with regard to the duration of persistence of virus in the semen, alongside substantial uncertainty in the duration of persistence in each individual," the authors wrote. 

Oropouche virus in semen, other body fluids

In related news, Dutch researchers yesterday reported the detection of Oropouche virus genome in semen and other body fluids in a traveler. Oropouche-specific Immunoglobulin M has recently been detected in 6 of 68 newborns with microcephaly (small head and brain), and vertical (mom-to-fetus) transmission of the virus has led to fetal death.

The report, published in Emerging Infectious Diseases, was based on samples from a male patient returning to the Netherlands from Cuba in August 2024. The patient recovered from illness, but the virus genome was still detectable in all samples except feces (urine, blood, and semen) up to 32 days after symptom onset.

Sexual transmission of the virus has not yet been determined, but the authors said their findings indicate its potential. 

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