How Covid-19 Immunity Compares to Other Diseases

If you get COVID-19 and you recover from it,

does that mean you're immune to the virus?

And even if you were to become immune,

how long would that immunity last?

Now we're still waiting on studies

to really give us definitive answers to these questions.

But in the meantime I think what can help us

understand COVID-19 immunity,

is thinking about our body's responses to other infections

and I kind of think of it as an immunity spectrum.

So what I wanna do now,

is talk us through some examples

along that immunity spectrum to help us better understand

where COVID-19 might fit in.

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On one end of the spectrum is Varicella-zoster virus,

the virus that causes Chickenpox.

And you might remember from your own childhood,

that if you get Chickenpox once

you usually develop a lifelong immunity to it

and you don't get it again.

This kind of lifelong immunity

happens because of antibodies.

Something you've probably been hearing loads about recently.

Antibodies are proteins made by our immune system

that protect us from harmful things.

Those can be infections like viruses and bacteria,

but also toxins and cancer cells.

With Chickenpox,

your body churns out antibodies

that are in it for the long haul.

And it also has cells

that are ready to make more antibodies.

Should you meet the virus again,

you can get exposed to viruses through natural infection

or this is a preferable way, you get immunized.

Meaning you get a vaccine that introduces your body

to a weakened version or a dead version of a virus,

so that your body knows what to recognize

and it mounts a solid immune response

that stops you getting sick.

And if you didn't get sick with Chickenpox as a kid,

you get two shots of the vaccine

that gives you longterm immunity.

Now, some people who have a weakened immune system

can get Chickenpox a second time,

and in fact,

our bodies are never able to get rid of the virus totally.

It stays latent inside our nerve cells

and in around one third of people,

the virus reactivates later in life and causes Shingles.

So how does COVID-19 compare to this example,

obviously the ideal situation would be

that you get COVID-19 once and that's it.

You're immune forever to the virus that causes the disease.

Unfortunately, this doesn't seem that likely.

And here's why.

There were early studies showing

that when people recover from COVID-19

they do have antibodies in their system,

but because this is such a new infection.

One, we're not sure how long those antibodies

hang around for and two,

there are some reports of those antibody levels

dropping really low, just a few weeks after infection.

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Here's another example, Whooping cough,

this is caused by a bacteria,

and usually if you get infected once

that immunity lasts from 4 to 20 years.

So quite a big range.

Because immunity fades over time.

The CDC recommends you get vaccinated

against Whooping cough,

but even with that,

you need to get booster shots.

Those are shots that you get your initial vaccinations

to make sure you stay protected over a period of time.

So even if we do develop a successful vaccine for COVID-19,

maybe that vaccination scenario will be similar to

Whooping cough where you get your initial doses of vaccine,

but then you have to get booster shots as well.

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So here's our next example.

H1N1 Influenza, also known as Swine Flu.

Studies have shown that immunity to H1N1

can last anywhere from 2 years to 10 years.

This is a strain of flu that caused a pandemic in 2009

but now circulates pretty regularly

alongside other common flu strains.

And with the flu the reason that we're getting

new flu shots every single flu season,

is because flu strains are changing.

And so literally every summer in the Northern hemisphere,

scientists are racing to predict

which flu strains are gonna hit us.

And what kind of vaccine they need to make

for that specific flu season.

Some experts predict that SARS-COV-2

will follow that same path as H1N1.

Meaning it causes a terrible pandemic at first

but then circulates much more like a regular virus

after the fact.

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Now when it comes to figuring out where the new Coronavirus

might fit on the immunity spectrum.

I think our best bet

might be to compare it to the original SARS Coronavirus.

SARS stands for Severe Acute Respiratory Syndrome,

and that's caused by the Coronavirus that emerged in 2002

and caused a pandemic in 2003.

Infecting more than 8000 people around the world.

Studies of SARS patients who recovered,

showed their antibody levels peaked around 2 to 4 months

and that they offered protection for 2 to 3 years.

So is this a timeline that we might consider

for SARS-COV-2.

Well, there are some studies that show

that when our bodies are infected with SARS-COV-2,

we produce what we call a neutralizing antibodies.

And these can stick around and offer protection

for a couple of weeks.

That's what the early studies are showing.

But clearly a couple of weeks is a ways off

from two to three years.

I think the glimmer of hope might be

that there's so much genetic similarity between SARS-COV-2,

and SARS-COV-1.

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Another good comparison we have right now

is to the four Coronaviruses that caused the cold

immunity to these seasonal Coronaviruses

starts fading just after a few months and within a year.

Most people are vulnerable to reinfection,

meaning it won't go away.

It will still infect people,

but it won't cause such serious disease

and it won't cause so many infections.

So that's a possible scenario that we might see

with the new Coronavirus.

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So on the other end of the immunity spectrum

compared to where we started is HIV.

People with HIV do develop antibodies to the virus,

but either those antibodies don't stick around for long,

or the virus has really cunning ways

to hide from the antibodies.

That's partly because HIV is constantly mutating

every time it's replicating inside the body

that makes the virus a moving target for our immune system.

Some good news on the COVID-19 front,

is that this Coronavirus does not seem to mutate

anywhere near as frequently as HIV mutates.

That means it stays a much more consistent

and it means we have far less of a moving target.

And because of that,

some experts are saying that reinfection

with the new Coronavirus could be less likely

just because the virus isn't changing so much.

So our immune systems recognize it and know how to fight it.

But I still think it's way too early

to be saying that reinfection is unlikely

just because of how new this virus is

and how much we're learning day to day.

So we don't know exactly where COVID-19

is gonna fit along this immunity spectrum.

But let's say you get infected with the virus

and it does give you antibodies that hang around for months,

maybe even a year or so.

In that scenario,

you can start thinking about herd immunity

as one way out of the pandemic.

Herd immunity is when a significant proportion

of the population has become immune to a disease.

Either through becoming infected or being vaccinated,

and when herd immunity is achieved,

it stops a disease spreading like wildfire

through a population.

That exact proportion of people that need to be immune

to a disease in order to achieve herd immunity.

It varies from pathogen to pathogen

and it depends on how infectious a microbe is.

We're still a ways off from thinking about herd immunity

as our way out of the COVID-19 pandemic

for at least two reasons.

The first being that we just don't know yet

how long those antibodies will hang around for

and how protective they'll be.

But second, because for herd immunity for COVID-19,

you'd need between 50% to 70% of a population

to become immune.

And we don't have a vaccine yet,

meaning we'd have to see a lot of people just get sick

from the virus and that's not

a feasible way out of the pandemic.

And finally, there's that question about antibody testing.

I think if we get studies that show us

how protective antibodies are to this virus

and how long those antibodies stick around.

Then in that case,

widespread antibody testing could be really useful,

especially if it's a quick fingerprint blood test

to help us understand who is immune,

for whom is it safe to go back to work

and how quickly could we start resuming normal activities?

But even if a large number of people have been infected,

recovered, and have immunity,

it's still not gonna trigger a sudden reopening of society.

There's gonna have to be a gradual peeling back

of containment measures like sheltering in place

to make sure that we're constantly guarding

against a second wave and against future outbreaks.

And that's gonna be our reality until we have a vaccine.

Thanks so much for watching.

Drop your questions here in the comments below

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