(gentle music)
- [Narrator] If you've been vaccinated against COVID-19
or if you've had an a COVID infection,
how long are you still protected?
It's super complicated,
but we do know that the immune system
learns to fight COVID-19 through vaccination
or in a less predictable way, from infection.
And how your immune system is primed
may have an impact on your long-term immunity.
- What happens during an infection is the virus comes in,
in this case, in your nose and your upper respiratory track,
and starts to replicate in the lining of your nasal passages
and eventually the linings of your lungs.
The virus causes damage when it does that,
killing cells and actually inducing more
and more inflammation that's causing damage.
- [Narrator] So vaccines give your immune system a leg up
in the race against the virus.
One of the early lines of defense
your immune system deploys is antibodies.
And in the case of vaccination or infection,
your body makes a ton of them.
These are tiny proteins
that can lock onto parts of the virus.
Most of the vaccines stimulate production of antibodies
that will lock onto the spike protein
that sticks out of the virus.
- And so the virus needs that spike protein
to attach to cells and to enter.
And if you have antibodies that block that step,
then it prevents viruses from getting in in the first place,
and then spreading if it happens to slip
past that first wave of antibodies.
- [Narrator] These are called neutralizing antibodies
because they can prevent the virus from entering your cells.
Right after vaccination or infection,
most people have lots of antibodies.
Though, in the early stages of your immune response,
they might not be the best match against invaders.
- And so basically if you happen to encounter a virus
right in that early period, those antibodies,
what they're doing is they're bouncing on and off the spike.
- [Narrator] But antibodies evolve,
even as they fight invaders.
B cells create tons of variations of antibodies
by scrambling their genetic code.
And some of those new antibodies
are better at binding to the virus than others.
And the B cells that make the best antibodies
are given the signal to make more, faster.
- There's a training process
where the B cells that produce these antibodies
are competing with each other to figure out who's the best.
And it's only those cells that stick around
and produce those antibodies.
- [Narrator] Some research suggests
that antibodies of COVID-19 survivors continue to evolve
for several months.
It's a good thing the antibodies get more efficient
because that initial spike in antibodies, that first wave,
eventually starts to drop off.
- About two months post infection or vaccination,
you'll have your, probably the highest levels antibodies.
And then they start declining.
Then they reach a plateau.
They do not decline significantly further.
They just stay put.
- You basically don't take nearly as much of a hit
as those antibodies are declining as you might expect,
because the quality of those antibodies is improving.
- [Narrator] Researchers don't yet know
what levels of antibodies are protective
against disease or infection,
or if antibody levels are the best measure of immunity.
They are however relatively easy to measure
compared to other immune responses.
- We actually do not know what the precise effect
of those waning antibodies in protection,
the virus, let's say categories of protection might be.
- [Narrator] But that decline in antibodies
could have consequences if they wane too much
in the presence of a lot of virus.
But another line of defense,
the memory arm of your immune system,
may persist in your body for months, maybe even years.
- There are many layers of immunity beyond just antibiotics.
And so all of these things are attacked
and that cellular memory
tends to be much more stable than the antibiotics.
And so even if you do get an infection
after you've been vaccinated
or after you've recovered from an infection,
you're not starting from the same point that you did
the very first time you encountered a virus.
- [Narrator] The T cells that kill infected cells
and the B cells that make new antibodies
learn about the threat as they fight the virus.
Or in the case of the COVID vaccines, a piece of the virus.
And after that threat is cleared,
cells known as memory B and T cells
hold on to information about that invader.
And then they lay in wait,
ready to jump into action if there's a new infection.
- You now have this pre-primed
or memory in your immune system
so that you don't have to go
through this whole process all over again.
And you don't have to wait
for your immune system to be re-educated.
So what we're seeing in some of these infections
and people who got vaccinated
is they get maybe a little bit of mild symptom,
but they don't get sick.
They don't end up in the hospital.
They don't end up with severe disease
because the backup plan of the immune system
is the memory B cells and memory T cells
that jump into action much more quickly
if you've been vaccinated.
- [Narrator] But there's some evidence that suggests
immunity after infection might be different
than immunity after vaccination.
And those that receive the vaccine
after recovering from an infection,
may actually have a stronger immune response
than those who have never been infected.
- The people are calling it super immunity, hybrid immunity.
There are different terms for this.
So you do seem to get some benefit of receiving the vaccine
from an immunological standpoint.
When your antibody levels are higher,
that may protect you for longer
because you've had essentially three exposures
to the immune system being trained.
You've had the infection and two doses of vaccine.
- [Narrator] But allowing your immune system
to prime by infection is really risky.
The virus could do a lot of damage
before your immune system catches up.
In one of the only long-term studies
to look at three types of immune responses to COVID,
antibodies, T cells and B cells,
researchers followed two groups of vaccinated people
for six months.
One group had been infected with the virus
and the other had not.
They found that vaccination helped
with long-term cellular memory.
- Memory B and memory T cells,
with some limits, they actually get better over time.
And after a bit of rest,
they actually become even more responsive.
- [Narrator] Sounds like good news,
but a growing body of evidence suggest
that vaccines protectiveness wanes somewhat
in the first year after vaccination,
although vaccines are still very effective
at preventing serious disease.
- They just observe that at six months
you'll have an increase in symptomatic infections
in the vaccinated population regardless of age.
If that is the case,
the third shot is absolutely recommended
because that's exactly what it's going to do.
It's going to boost your neutralizing antibodies further
and potentially help stop
this increase in symptomatic infections
in vaccinated people.
In my personal opinion,
this is an experiment I don't want to do.
Let's just stay ahead and include as many people
as they want to get the third dose.
I think at the moment,
it's far more risky to wait and see what happens.
- [Narrator] Some experts argue against booster shots,
at least for most healthy vaccinated people,
when much of the world remains unvaccinated.
In addition to the continuing dangers of COVID
for the unvaccinated,
they point out that the more COVID thrives,
the more it will mutate,
producing new variants that might be harder to fight.
- So the question is,
if we start doling out these doses in this country
and in Europe and in Canada because it will follow,
does that impact our ability
to get vaccines out to some of these lower income countries?
And does that prolong the duration of the pandemic?
And I think these are really complicated questions
that they just haven't seen answered adequately.
Immunologically speaking,
those first two shots are so much more important
than the third ones.
- [Narrator] For now, the CDC recommends booster shots
for certain high risk groups, including those 65 and older.
- It appears that your immune response
is also overall wane with age.
Also, if you are at high risk of exposure due to work,
coming into contact with a lot of people,
then also your chances of developing severe disease increase
just because you are exposed to much higher viral load.
Why not protect those people regardless of age
as much as we can?
- [Narrator] While there are still
many unanswered questions,
this is one of a few immune responses
to a virus studied so closely in real time,
which gives some researchers a glimmer of hope
that our understanding of the immune system
and how it battles viruses is getting better and better.
(gentle music)