Tackling infectious diseases
I was recently reading a document prepared by the World Health Organization (WHO), titled Ending the neglect to attain the Sustainable Development Goals: a road map for neglected tropical diseases 2021−2030, and what drew my attention was that many of these diseases are targeted for eradication or elimination. These 20 diseases affect more than 1 billion poor people around the world, are almost absent from the global health agenda, and are almost ignored by global funding agencies, but WHO has a plan in place to reduce their incidence by either controlling them, eliminating them, or eradicating them.
What’s the difference between controlling, eliminating, and eradicating an infectious disease? There are actually four ways to get rid of infectious diseases (page viii), and they progressively pave the way toward reducing the incidence of a disease or an infection to zero: (1) control: reduction of disease incidence; (2) elimination: reduction to zero of incidence of infection in a defined geographical area; (3) eradication: reduction to zero of worldwide incidence of infection; and (4) extinction: eradication of a pathogen, so it no longer exists in nature or in the laboratory.
Knowing this, it occurred to me that even though we hear about infectious diseases all the time (obviously COVID, but also the flu, AIDS, measles, and malaria, among many others), if we have the right tools — mostly vaccines, but sometimes other means, such as draining swamps and using mosquito repellents when fighting malaria, for example — along with financial resources, and political will, many of these diseases could actually be either stamped out significantly or eliminated.
This way of thinking is often missed when we hear about infectious disease outbreaks in the news. Efforts to address these outbreaks when they happen or their prevention through vaccination campaigns (when possible) is often all we hear about. But how about the possibility of eliminating, or even eradicate, any one of these diseases? I think that should be part of the conversation, too.
I recognize that it’s not that simple, often because of a lack of financial/physical/human resources and political will. Often, controlling an infectious disease outbreak can be very challenging to begin with, and eliminating or eradicating it isn’t in the cards yet.
A good case in point is the Ebola outbreak in Libera from March 2014 to June 2016. Mosoka Fallah, program manager of the Saving Lives and Livelihoods Initiative at the Africa CDC in Addis Ababa, Ethiopia, describes what it took to control that outbreak in a “World view” article he wrote in Nature on Nov. 22, 2022: To beat Ebola in Uganda, fund what worked in Liberia):
To succeed, we had to deputize members of the public — 5,700 of them at the peak of the crisis. We called them active case finders.
They went house-to-house, tracking sick people and all of their contacts across 1.6 million households. People needed to trust the messenger to believe the message. They would trust a neighbour more than a stranger clad in head-to-foot personal protective equipment (PPE).
…
When there was a confirmed case or high-risk contact, chiefs would ensure that local youths left rice and water for the household so that the members could voluntarily self-quarantine. To reduce stigma, local leaders hosted a community ceremony to welcome back anyone who had completed quarantine, with a reintegration package of food, cash and clothing.
Secret burials are a major driver of Ebola spread, so cultural sensitivity was also key. The virus is at its peak in corpses. It can spread through someone touching just a drop of blood or saliva or clothes that have been in contact with bodily fluids. To protect the living, the bodies of those who have died of Ebola must be handled by workers in full PPE, and there must be a thorough case investigation that includes immediate contact tracing.
In Liberia, we found that the earlier we could get people to a treatment centre, the better their odds of survival, because they would receive hydration, food and medication. So we made every effort to identify people with Ebola at the onset of symptoms. Contact tracers were embedded at Ebola hotspots 24 hours a day to monitor people’s temperatures. As survival rates increased, more people were encouraged to come to treatment units.”
Another case in point is the recent Ebola outbreak in Uganda (from Sept. 20, 2022, when the outbreak was officially declared, to Jan. 11, 2023, when the end of the outbreak was officially declared). Henry Kyobe Bosa, the national incident manager for Ebola and COVID-19 for Uganda in Kampala, describes how the outbreak was controlled in a “World view” article in Nature published on Jan. 26, 2023, Don’t wait for an Ebola outbreak to vaccinate people against it:
Institutional quarantine, meaning separating people who have been exposed to Ebola from their families in an isolation facility for 21 days, or even just quarantining at home, can be hard enough for those who have relatives to care for, or who need those 21 days of income to feed their families. But the measures we were forced to take in Kampala included 63 days of lockdown in two rural districts with a combined population of nearly one million.
The effect on people’s livelihoods and on the local timber industry was devastating. The societal disruptions that these interventions bring fuel people’s anger and distrust of public-health efforts.
But Bosa states in this article that the best way to prevent these outbreaks, or at least limit their incidence, is to vaccinate people, especially those who live in high-risk areas — areas that had outbreaks before, such as the band across Central and West Africa in which Ebola outbreaks have been reemerging almost every year since 2000 — or in areas in which access to sanitation and clean water is limited or inexistent. Vaccination campaigns are essentially the best way to reduce the suffering and the heavy death toll that diseases like malaria or cholera are taking on people around the world. And when vaccination campaigns are done persistently and regularly, they can ultimately eliminate or eradicate an infectious disease.
For example, in the case of malaria, a recent editorial in Nature, titled Half a million children die of malaria each year. We can change that, announced that the World Health Organization (WHO) had recommended a second malaria vaccine, developed by researchers at the University of Oxford in the United Kingdom and the Serum Institute of India in Pune. Massive vaccination campaigns using this vaccine and the first one (which was recommended for widespread use by WHO in Oct. 2021) promise to significantly reduce malaria’s toll on the human population, many of whom are children in Africa. As noted in the Nature article:
So far, [the first malaria vaccine] has been administered to more than 1.7 million children across Ghana, Kenya and Malawi. A further 18 million doses will be sent to 12 African countries by 2026. The WHO estimates that 40 million to 60 million malaria-vaccine doses will be needed annually by 2026. Demand is expected to grow to between 80 million and 100 million doses each year by 2030. The Serum Institute currently has the capacity to make 100 million doses of [the second malaria vaccine] each year, and this is expected to double to 200 million by 2025.
For many infectious diseases, controlling them through vaccination campaigns is already a huge success — one that is never a done deal, though, because vaccinations need to continue over time (especially children’s vaccinations). And elimination and eradication of other infectious diseases is already in the cards, with several infectious diseases are now targeted for eradication, including polio, malaria, measles, rubella, and two neglected tropical diseases: yaw and dracunculiasis. These efforts follow two major eradication successes: that of smallpox in humans in 1980 and of rinderpest in ruminants (animals that include cows, sheep, and goats) in 2011.
But eradication efforts can be complicated and can take a long time. The ongoing efforts to eradicate polio are a good case in point. These efforts started 30+ years ago and have led to a huge decrease in cases around the world, with now only a few cases left in Afghanistan and Pakistan (five in Afghanistan and two in Pakistan). But there are two types of polio vaccines: an oral vaccine and an injectable vaccine. The oral vaccine contains weakened polioviruses, that is, they are harmless but can grow and replicate inside the body, so they can generate an immune response. The injectable vaccine contains inactivated, or dead, polioviruses, which are also recognized by the immune system. Also, the oral vaccine curbs polio outbreaks better than the injectable vaccine, it’s easier to administer, and it’s cheaper. So, many polio vaccination programs have been using the oral vaccine.
But the weakened polioviruses in the oral vaccine can sometimes go back to their virulent form, and then they can infect people again. They are usually shed in human stool from people who have been vaccinated, and then the shed polioviruses — called vaccine-derived polioviruses — sometimes mutate in the wild to become infectious again. The more people are vaccinated (that is, the higher the vaccination rates), the lower the chances these vaccine-derived infections happen.
Unfortunately, in many parts of the world, many children are not vaccinated against polio. (According to the Centers for Disease Control and Prevention, children need to receive four doses of the polio vaccine: when they are 2 months old, 4 months old, 6 through 18 months old, and 4 through 6 years old.) As a result, vaccine-derived polioviruses have infected an increasing number of people, especially in recent years.
The solution? Ideally, it would be to increase vaccination rates (mostly of children). This is happening, but in some parts of the world more than others. As a result, in recent years, an increasing number of people have been paralyzed with vaccine-derived polioviruses. Since January 2020, vaccine-derived polio has shown up in more than 50 countries, and in 2023, it has paralyzed 246 people worldwide (per the Science article, Polio eradication effort struggles with end game, published on Sept. 22, 2023).
Another solution is to switch to the injectable polio vaccine, but that vaccine doesn’t contain outbreaks as well as the oral polio vaccine. Switching to the injectable vaccine works only if you have a high vaccination rate all the time. The catch-22 is that the oral vaccine reduces transmission but carries the risk that if vaccination rates are low, vaccine-derived polioviruses can still spread, and the injectable vaccine doesn’t reduce transmission, so if vaccination rates are low, wild polioviruses can still spread.
So, the Global Polio Eradication Initiative (GPEI), a public-private partnership led by national governments and six global partners, created two different versions of the polio oral vaccine (one in 2016 and one in 2021) that reduce the chances that the attenuated virus in the vaccine becomes infectious. Now, it remains to be seen how these different versions of the oral vaccine will reduce the occurrence of vaccine-derived polioviruses.
In the meantime, the best option is probably to increase vaccination rates with either the safer oral vaccines or the injectable vaccines in parts of the world that have the infrastructure for high vaccination rates. As Tom Frieden, former head of the U.S. Centers for Disease Control and Prevention, stated in an interview article published in Science, Polio eradication effort struggles with end game:
At some point, you’re going to want to stop [oral polio vaccine] vaccination, but that point is not for a long time. You can’t do it while you’ve still got spread, because [injectable polio vaccine] does not reduce transmission, it reduces disease. So I don’t think [oral polio vaccine] failed, and [injectable polio vaccine] is the answer. They both have got a really important role.
Bottom line: Eradicating an infectious disease can be difficult and can take time, and high vaccination rates and a robust health infrastructure are critical to make such eradication efforts successful. Not to mention the relentless efforts of dedicated organizations, sustained financial support, and the political willpower to push forward and address hurdles along the way.
Eradicating an infectious disease is also an amazing feat. When you think about solving other big societal issues — such as poverty, hunger, access to safe drinking water, or access to electricity — we haven’t yet been able to solve them on a global scale. For infectious diseases, we have shown that we can do it, at least for smallpox and rinderpest. As Frieden said in the Science article, “Eradication is the ultimate in both equity and sustainability, because it is for everyone and forever.”
What may be difficult to appreciate, though, is the number of lives saved from vaccination efforts in many parts of the world. When there are no vaccines and limited medical interventions for a given infectious disease, people get sick or die. This toll is what we often remember and requires a significant amount of coordination from medical professionals and members of the affected communities — such as those described earlier by Fallah (Africa CDC) about Ebola. But when vaccination rates are high, then usually, fewer people get sick, and it may not be as obvious the extent to which the vaccines have saved lives and minimized disruptions to societies and economies.
The ongoing efforts to tackle infectious diseases are encouraging, and they show what can be accomplished in the future. They also provide tangible goals — control, elimination, and eradication of infectious diseases, along with increased vaccination rates, strengthened public health services, and improved living conditions — that will help us tackle infectious diseases and alleviate its burden on the global human population.
