As if you need any more proof that twenty-twenty is shaping up to be an interesting year, just
take a look at some of the year’s most popular buzzwords so far - first it was social distancing;
then it was flattening the curve; and now it’s herd immunity.
But what exactly is “herd immunity” - does it really mean we all need to get infected
to get immunity?
Let’s take a look at what the experts are saying and get COVID-19 herd immunity explained.
Simply put, herd immunity is what happens when a significant portion of the population
is immune to an infection, which slows down or stops the spread of the infection.
Herd immunity isn’t about protecting each individual person - it’s really about preventing
a widespread outbreak of infection.
Herd immunity means that each person who does contract the infection won’t be able to
spread it to as many, if any, other people.
The more people in the group, or herd, that are immune to the infection, the less easily
the infection can spread through the population.
To visualize how herd immunity works, you can picture a group of dots representing people.
Blue dots are people who are immune to the infection, and yellow dots are people who
are not immune and are therefore susceptible to the infection.
A red dot represents an infected person.
A red dot can infect any yellow dot it comes into contact with, turning the yellow dot
red.
The red dot cannot infect the blue dots.
If enough of the dots in the group are blue, or immune, the red dot won’t be able to
spread to the yellow dots as easily.
But if too many of the dots are yellow, or susceptible, the infection can quickly spread
throughout the group.
Herd immunity is most important for protecting the most vulnerable and at-risk people in
our communities.
Older people, very young children, pregnant women and people with underlying health issues
stand a higher risk of experiencing serious complications if they contract an infection.
People with compromised immune systems, like cancer patients undergoing chemotherapy, are
also at higher risk from infections.
These vulnerable people can’t be vaccinated due to the potential for serious side effects
from even the weakened vaccine, so they rely on herd immunity to keep themselves safe.
It’s important to note that herd immunity only works for infections that spread through
person-to-person contact.
Some infections spread only through contact with infected surfaces, not people, so herd
immunity is ineffective at preventing their spread.
For example, you might contract a tetanus infection after stepping on a rusty old nail,
but you won’t be able to spread that infection on to other people that you come into contact
with, so herd immunity is irrelevant to tetanus infections.
For infections that do spread from person to person, like COVID-19, once a certain percentage
of the population is immune to the infection, it’s ability to spread slows or stops.
The precise percentage of people that need to be immune is called the Herd Immunity Threshold,
and the threshold is different for every infection depending on just how contagious it is.
Some infections that aren’t very contagious only need about forty percent of people to
be immune to prevent the infection from leading to widespread outbreaks.
In most cases, though, the herd immunity threshold is much higher - we need eighty to ninety-five
percent of the population to be immune to stop most infections from spreading widely.
So if eighty percent of the population is immune, that means that four out of every
five people who come in contact with the virus won’t get sick, and they won’t spread
the virus on to other people.
Measles is a great example of herd immunity in action.
Before nineteen sixty-three, measles infected three to four million Americans each year,
and killed between four-hundred and five-hundred people every year.
Once an effective measles vaccine was developed and a significant portion of the population
was vaccinated, the Herd Immunity Threshold was met and in the year two-thousand, the
American government declared that measles had been eliminated in the U.S.
And yet, we still hear stories of localized measles outbreaks from time to time - like
the twenty-fourteen “Mickey Mouse Measles” outbreak that saw fifty-two people become
infected with measles after a New Zealand teen with the disease visited Disneyland in
California.
The scary thing about measles is that it’s extremely contagious - each person with measles
can infect another ten to fifteen people.
Because measles is so contagious, it also has a very high Herd Immunity Threshold - ninety-five
percent, or nineteen out of every twenty people needs to be immune to prevent an outbreak
from spreading.
Anytime a population dips below that threshold, whether because they can’t be vaccinated
or because they chose not to be, measles can once again begin spreading from person to
person.
In the case of COVID-19, when the virus first began spreading in humans no one was immune
to it.
The virus encountered no resistance and so it spread quickly from person to person, leading
to major outbreaks like what we’ve seen in Italy and New York.
The more people who become immune to the virus, the slower it will spread and the faster the
outbreak will end.
Early estimates are that seventy percent of the population will need to be immune for
herd immunity to be effective, but we still don’t know for sure - more on that in a
bit.
First, let’s find out how we can actually achieve herd immunity.
There are two ways that herd immunity happens - a significant portion of the population
needs to either contract the infection, or get vaccinated against it.
Vaccines are the safest and most effective way to achieve herd immunity, but natural
herd immunity can happen when a significant portion of a population ends up getting infected.
Back in two-thousand ten, after the global H1N1 Swine Flu pandemic, researchers in Norway
determined that nearly sixty percent of the population now had some form of immunity to
the infection, and in many cases this was the result of natural immunity after contracting
the disease.
Olav Hungnes, a researcher at the Department of Virology at the Norwegian Institute of
Public Health, has said: “Even though many acquired immunity through infection, we believe
that vaccination may have been responsible for most of the increase.”
Although an H1N1 vaccine was eventually developed, natural immunity certainly played a part in
helping Norway to achieve herd immunity to H1N1.
So, does that mean we should all be rushing out to try and “catch” COVID-19 now so
that we can “get it to get it over with”?
Umm, not exactly.
To find out why that’s a really, really bad idea, let’s see what the experts at
John Hopkins have to say about COVID-19 herd immunity.
According to John Hopkins’ Bloomberg School of Public Health, we’re a long way from
achieving herd immunity against COVID-19.
Based on early data about the contagiousness of the infection, experts estimate that the
Herd Immunity Threshold for COVID-19 is at least seventy percent - that means seven out
of every ten people would need to either be vaccinated against COVID-19, or get the disease
to develop natural immunity.
Since we don’t yet have a vaccine, natural immunity might sound like a good alternative,
but the researchers at Johns Hopkins are also very clear about the fact that natural herd
immunity is not the answer to beating COVID-19.
First of all, natural immunity means that people need to actually get the disease first
in order to give their body a chance to develop antibodies against it.
This means they may have to get sick and experience symptoms, and that can put them at risk of
serious complications.
COVID-19 is up to ten times more deadly than the normal flu, and even young, otherwise
healthy people have been hit with serious and even fatal cases.
That’s another major reason why natural immunity is dangerous - we still don’t know
enough about COVID-19 and the SARS-CoV-2 virus to know for sure how natural immunity to it
works.
Research is still ongoing into how the virus spreads and why some people experience more
severe symptoms than others.
Researchers aren’t even sure if getting the infection actually gives you any immunity
at all against future infections.
If COVID-19 is similar to other coronaviruses that have been studied, getting sick probably
provides some level of immunity, but only for a matter of months or years, not for life.
Researchers are still trying to understand how immunity to COVID-19 works, but we just
don’t have all the answers yet.
Perhaps the most important reason why we can’t rely on natural immunity to achieve the herd
immunity threshold for COVID-19 is because of the huge burden that would put on our health
case system.
Quicker is definitely not better when it comes to infections - we just have to look back
at the nineteen-nineteen Spanish Flu outbreak to see what happens when natural immunity
plays out on a huge scale.
In Philadelphia, one of the hardest-hit cities, hundreds of people were dying every single
day and hundreds of thousands of people were sick.
Every one of the city’s thirty-one hospitals were over capacity, and the city’s morgue,
which was only designed to hold thirty-six bodies, was quickly overrun.
The city rushed to build five temporary morgues, but it still wasn’t enough - unembalmed
bodies piled up in the corridors of hospitals, on front porches and even in the streets,
and the smell of death was everywhere.
The Johns Hopkins team lays out a worst case scenario for COVID-19 - if no physical distancing
measures were in place, the virus would spread very quickly, infecting many people in a matter
of months.
The huge number of cases would crash the healthcare system and we would see a very high death
rate.
To achieve herd immunity to COVID-19 through natural immunity, hundreds of millions of
people just in America alone would have to get sick all at once, a huge burden that our
already stretched healthcare systems simply cannot handle.
So what does this mean for us going forward?
Well, we obviously know we shouldn’t be trying to catch COVID-19 to speed up herd
immunity, but how long will it take for things to go back to normal?
Johns Hopkins lays out a best case scenario for containing the spread of COVID-19, too.
If we can maintain current physical distancing measures, we might be able to maintain or
even reduce the rate of infections and buy ourselves time until herd immunity can be
achieved through a vaccine.
This would require the entire population to continue to cooperate and maintain strict
physical distancing measures for up to a year or more - and that’s the best case scenario.
The most likely scenario falls somewhere in between.
It’s probably not realistic to expect people to maintain current social distancing for
years, but Johns Hopkins predicts that some form of physical distancing measures will
need to be in place for at least a year or more, and that life won’t truly go back
to “normal” until we can develop a vaccine.
But, they also point out that things probably won’t always be as strict as they are right
now.
As the physical distancing measures we’re already doing start to pay off, and as more
people become naturally immune to COVID-19, we’ll see less of the explosive outbreaks
we’ve seen so far in this pandemic.
As the rate of infection falls, some physical distancing measures can be relaxed; if the
infection rates start climbing again, those measures might have to be reintroduced to
control localized outbreaks.
According to Johns Hopkins, until we have a vaccine we won’t be able to rely on herd
immunity to keep us safe from COVID-19.
And that’s still a long way off - scientists are working furiously to develop a vaccine,
but it takes a long time to create, test and mass-produce a safe and effective vaccine,
and more time to get the majority of the healthy population vaccinated.
Until then, physical distancing measures and frequent handwashing are the most effective
ways to prevent the spread of COVID-19.
It’s going to take a prolonged effort on all of our parts to contain the spread of
the virus until a vaccine is available and we can safely achieve herd immunity to COVID-19.
Now go check out “COVID-19 vs H1N1 Swine Flu - How Do They Compare?”, or this other
one instead.
If you’re going to be stuck at home for a while yet, we can at least keep you entertained!