If there is a word we need to strike from this conversation, it’s the mythical “herd immunity” in SARS-CoV-2.

Peter Panum “gets” the measles

Mikka
Peter Panum

In 1846 a Danish physician named Peter Panum [@plpanum1967] made himself enough of a nuisance at home in Copenhagen to be relocated to the end of the world. Or, more precisely, the Faroe Islands. While measles were popping up every once in a while in Denmark, Tórshavn and the small communities spread over the dozens of islands that comprise Faroe, had been mostly spared. Until the time Panum arrived.

A massive wave of the virus rushed over the population, infecting anyone from young to old. This was, Panum surmised, because there had not been a measles outbreak before, thus no immunity.

From Panum’s work came one of the great discoveries in vaccine history: some viruses, such as measles, elicited a life long presence of antibodies in the serum, essentially making anyone who had had the infection or a vaccine immune to them.

Measles are an outlier. And to understand them, we need to go back, all the way, to a time before man was a glimpse in the eye of evolution. Most animals didn’t even have jaws, yet.

We have to go back, Marty!

When and how our adaptive immune system developed is a mystery shrouded in time [@flajnikOriginEvolutionAdaptive2010]. Sure is, that today’s jawless vertebrae have developed a slightly different kind of adaption while jawed vertebrae (such as humans), went the way of developing more adaptive variable lymphocyte receptors (VLR) [@boehmVLRbasedAdaptiveImmunity2012].

Sure is one other thing, our adaptive immune system evolved to protect the kind of “herd” prevalent during this time: small clusters of animals, wary of all outsiders, even those of their own species. Any pathogen entering such a herd would remain until all members of the cluster either had been infected and developed an immunity or had died.

For this, this immunity would not have to last long. Once every member of the cluster had been infected, with no new hosts to migrate or mutate over, the threat was contained. The pathogen would die out quickly, unable to find new suitable hosts.

In a world in which the fight for survival is a daily reality, this was fortuitous. Maintenance of an adaptive immune system isn’t the most energetically expensive thing but, still, required energy for development and upkeep. Nature, on the other hand, optimized towards least expensive systems.

We’re evolving too fast

Mankind changed this game. Its mental and intellectual capabilities far exceeded evolution’s drive to optimize. Within less than the blink of an eye of evolutionary time, humans developed from small, secluded, clusters into a global community of nearly eight billion people. Evolution counts its successes in hundreds of thousands of years, mankind not only expanded at blazing speeds [@mcevedyAtlasWorldPopulation1978] from four million to almost eight billion in less than 15000 years, the past 100 years also led to a more and more connected world in which the definition of tribal or herd segregation has all but vanished.

Evolution, however, brought a second line of defense into the mix. If a pathogen returned (say from migrating animals), a “memory” function ensured that second and later infections were met faster and much more vehemently. Maintaining memory cells is energetically much cheaper than keeping up the presence of antibodies in the serum while still offering protection vastly superior to that of an immune system required to learn the pathogen’s features every time it encounters it.

After the attacks on September 11 2001 the world of bioterrorism research revisited old plagues as possible attack vectors. Smallpox, a disease considered to be as good as eradicated, was one of those possible vectors [@cohenBioterrorismSmallpoxVaccinations2001].

Enter Edward

Mikka
Edward Jenner

Edward Jenner’s name should be familiar to anyone. Observing, that stable workers in frequent contact with cows infected with cowpox did not contract smallpox at the same rate as others, he surmised that an infection with cowpox, a comparatively much less injurious and deadly disease, conferred an immunity to smallpox. The details of his initial experiments, including the smearing of cowpox pus into surgical incisions, might sound strange, but the results were groundbreaking [@riedelEdwardJennerHistory2005].

Besides coining the term vaccine (from “vaca,” cow, in Latin), Jenner’s discovery also ended the previous practice of “variolation” in which smallpox were inoculated into non-immune adults in an attempt to create immunity barriers. Such variolations were only marginally successful, killing many of the subjects in the process and even kicking off further smallpox epidemics.

The human mind compensated for the shortcomings of our bodies. Instead of waiting to be struck, we now had a way to strike, in a milder and less injurious way, first.

Back to the Herd

Those post-9/11 studies show, that smallpox vaccines convey only limited immunity over the first few years. So, how were we able to mostly vanquish this demon? The answer lies in the second part of the adaptive immune system, its memory. Smallpox has an incubation period of 10 to 14 days. During this time, infected persons are not infectious themselves [@ClinicalDiseaseSmallpox2019]. 10 days is enough time for the memory part of the adaptive immune system to “ramp up” and return serum antibodies to a neutralizing level. While infections are not made impossible, they are largely fruitless to the virus, which is killed long before reaching a stage where it turns the host into another spreader.

SARS-CoV-2 is different. Here, it takes less than seven days for symptoms to arise[@eliasIncubationPeriodCOVID192021]. Like most viruses, SARS-CoV-2 uses the host’s own defenses to travel (Norovirus uses the diarrhea caused by the host’s attempt to flush it out, Rabies kills and leaves cadavers to be eaten by predators, while Coronaviridae use coughs and increased respiration). However, in this case hosts are infectious days before symptoms, often three to four days after infection. Short incubation means that memory cells do not have enough time to mount an effective response before infectivity happens.

What does this mean?

It means, that Coronaviridae are no measles. Duh!

It means, that there is no real way to create a herd immunity, short of having every person on the planet be infected or freshly (2-8 weeks after the poke) vaccinated at the same time. Any other scenario leaves gaps through which the virus, either using unvaccinated or vaccinated hosts with 9+ weeks since the last vaccine, can slip.

Instead, vaccines serve as a moderator. Previously moderate and severe courses of a disease turn into mild ones. Many infected persons remain asymptomatic or feel only slight discomfort.

Given the reality of this pandemic, the fact that there is no path to true herd immunity, our options are simple: reduce the economic and social impact, re-enable a somewhat “normal” together, and take the massive strain caused by moderate to severe and critical courses of the disease off the health care system [@moghadasImpactVaccinationCOVID192021].

When this “normality” happens, that’s in the stars. Today, only weeks before the turn of the year, it is clear that neither Antony Fauci’s “End of 2021” nor the WHO’s “End of 2020” were reasonable estimates.

So Anti-Vaxxers, Corona-Partyists, and Mask Mandate Misfits aren’t to blame?

Oh, they damn well are. Masks, social distance, and vaccines contribute heavily to a reduction in hospitalization numbers.

While masks and distance won’t reduce the number of infections, they greatly decrease the amount of simultaneous ones, thus reducing the day-to-day load on hospitals from more than mild presentations.

While we’re probably not able to end this pandemic on our terms, we are capable of cushioning its impact and reducing its strain on the population, social and economic factors, and the health care system. Every mask worn, every vaccine received, and every distance kept, lowers the footprint of the disease.

We just need to stop using SARS-CoV-2 and COVID-19 interchangeably. And we need to quit the myth of herd immunity or preventative measures. We can reduce the incidence of COVID-19 greatly, but we can not end the pandemic.

Mask or not, vaccinated or not, distanced or not, we will (sometimes even more than once) get infected. We’re mostly powerless in this regard. What this infection means to most, a mild malaise or death, two days of Netflix or an overtaxed and failing health care system, however… that’s up to us.

But neither mask wearing or vaccine receiving will protect us from being infected or others from us. The pandemic, regardless of its origin, is at this point no one’s fault. We have been dealt a shit show of global proportions and we need to get used to the idea that this will hurt. Badly, no matter what we do. We are tasked to assume the responsibilities to, while we won’t prevent it, cushion and reduce the pain this has caused and will cause for months to years to come by doing everything we can.

Disclaimer

The author slept through most of his immunology classes in med school. He successfully completed the course and later did a year in evolutionary microbiology research, but he is no epidemiologist. He is a medical professional, has a degree in public health and virology, and works in a COVID-19 ward in a large hospital, where 85% of all patients are not vaccinated. He thus strongly dislikes anti-vaxxers and anti-science BS.