We have learned over time that Covid vaccine immunity is short-lived and requires boosting to … [+] maintain protection.
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Dr. Mark Kortepeter explains the differences between smallpox, which was eradicated in 1980, and Covid-19 and why the virus is most likely here to stay.
Periodically, someone asks me the question, “Can we eliminate Covid-19?” What they may not expect is my long answer. Thus far, despite our extensive knowledge of viruses and sophisticated medical research capabilities, there is only one human disease that we have eliminated: smallpox. Smallpox was one of the deadliest scourges throughout history, killing millions, maiming and blinding countless others, and leaving the rest with disfiguring scars. Its elimination from the human population stands as one of the shining achievements of public health.
So, when considering the potential for eradicating Covid-19, it is instructive to assess what properties of smallpox helped us to eliminate it and consider how the SARS-CoV-2 virus, which causes Covid-19, compares.
There are four aspects to consider: 1) Properties of the virus, 2) Manifestations of the disease, 3) Properties of the vaccines, and 4) Aspects of the society at the time. The most likely scenario with Covid is that it moves from a pandemic threat, which is a global widespread infection, to an endemic challenge, which circulates regularly in the population similar to a seasonal virus like the flu.
Properties of the virus
Smallpox only infects humans. There is no carrier state, meaning there aren’t people or animals who carry the virus without showing symptoms. If someone survives the disease, they can no longer transmit it. So, once we eliminate the disease in humans, there are no animal reservoirs harboring the virus that can infect humans again at some future date. This is different from coronaviruses, like SARS-CoV-2, which may be found in nature in bats and can jump to other animals, including our own pets, such as cats, dogs, ferrets, and hamsters. Even though we haven’t seen a lot of spread from animals to humans, if we could eliminate Covid-19 in humans, the risk remains that animals could eventually bring the infection back to the human population.
The genome for smallpox is DNA, while the genome for SARS-CoV-2 is RNA. This simple difference has enormous implications, because DNA is more stable, which means that countermeasures, such as vaccines, diagnostics, and treatments, continue to be effective against the smallpox virus over time. With SARS-CoV-2, the virus has continued to churn out a steady number of new variants, which have reduced the effectiveness of our vaccines and treatments. Essentially, we are playing constant catch-up against the virus.
Manifestations of the disease
Many infectious diseases can be difficult to distinguish from one another in the first couple days, when patients feel unwell, and have a fever or body aches. Even when the smallpox rash first develops, doctors could confuse smallpox with other rash-causing diseases, such as chickenpox, typhoid, and syphilis. However, once the classic pus-filled lesions developed on the face, hands, and chest, it didn’t take a rocket scientist to make the diagnosis. This was a key element for eradicating smallpox – the ability to find victims, even in the most remote regions of the world. By identifying those infected easily, the eradication teams could make strategic decisions on where to focus their vaccination efforts. The longer incubation period of 10-14 days on average for smallpox (versus an average of 3-6 days, depending on the variant for Covid) also provided the opportunity to vaccinate someone after exposure and still provide protection.
One of the critical challenges with Covid-19 is the difficulty of discerning whether someone has Covid-19 or a myriad of other respiratory viruses, such as influenza, parainfluenza, rhinovirus, or other less severe coronaviruses. To add to this challenge, up to 40% of those infected can have very mild or even asymptomatic infection. Meanwhile, they can still be spreading the virus unknowingly.
Properties of the vaccines
We were enormously successful in cranking out brand new vaccines for Covid-19 in the shortest time frame ever, but we have learned over time that the vaccine immunity is short-lived and requires boosting to maintain protection. This is completely different from the experience with smallpox. The smallpox vaccines provide long lasting immunity, potentially lifelong for reducing illness severity. This makes it much easier to protect the whole population if you only need to vaccinate them once.
Another key property of the smallpox vaccine allowed the public health workers to vaccinate populations in the most remote areas of the world, even those areas without electricity, because the vaccine didn’t require refrigeration in order to remain potent. The smallpox vaccine was lyophilized (dried) in a bottle until it was needed. Then, the vaccinator mixed in a sterile liquid and scratched the live virus vaccine into the skin with a specialized two-pronged needle shaped like a tiny pitchfork. The vaccine created a local pus pocket on the skin, which left a permanent scar, providing lifelong proof of successful vaccination, even without a vaccine card. Workers could carry a batch of needles and boil them over a fire to sterilize them after a days’ vaccinations for reuse again the next day. Vaccinators could travel with a sack of equipment and range far and wide. Doing something similar would be very challenging with the current Covid-19 vaccines, because they require a power source, such aselectricity, generators, and batteries, to maintain sub-zero temperatures to keep them viable – not so simple in remote areas.
Aspects of Society
The ability to eradicate smallpox also depended on certain aspects of society in the 1900s. We had a less mobile population. Smallpox moved across the globe over centuries at the speed of boats. Covid-19 moved across the world in mere weeks and at the speed of jets.
In the 1900s, there was also a strong belief in the ability of science and vaccines to solve medical problems. In the last major outbreak of smallpox in New York City in 1947, photographs show people in winter coats standing in long lines stretching several blocks waiting to receive their vaccination. That’s determination. In the United States today, only 66.7% of the population is fully vaccinated against Covid-19 – even though we are over two years since the virus first surfaced.
Eliminating a disease requires unity of will and effort. We had enormous international consensus behind the smallpox eradication effort – in fact, the effort was first proposed by the Soviet Union. Somehow, I don’t think we could achieve such cooperation today – either internationally or in the United States. Covid-19 has done a lot to reveal the challenges of building a unified response.
Mustering political will may also depend on the severity of the disease. Smallpox killed 30% of victims and victims were transformed with pus-filled lesions all over their bodies within days. It is perhaps less easy to ignore or deny its very visible impact. The death rate for Covid is far less.
Can We Eliminate Covid-19?
Based on the comparison of these two viruses and the very different diseases they cause, I am very skeptical that we could ever eliminate Covid. I think it is here to stay. That’s not to say it’s all doom and gloom. In the short time we have dealt with Covid, we have generated effective vaccines, treatments, and diagnostics rapidly. We have turned it from a disease that filled our intensive care units and nearly broke the medical system to one that, while still a risk to the most vulnerable, in many of the vaccinated now causes a “bad cold.” I am optimistic that we will continue to develop new ways to tame the disease. I also like to think that we have learned something about our preparedness so that for the next pandemic disease, we might move a little faster, with greater purpose, and greater unity.