(pensive music)
- [Narrator] Throughout the pandemic,
athletes have been the most tested population
on the planet, sometimes providing examples
of emerging theories about COVID-19.
And as countries around the world continue
to fight back COVID-19,
attention has turned to Tokyo
where the Olympics are under way.
One challenge some athletes are facing:
testing positive for the virus,
despite having been vaccinated.
This isn't the first we've heard of this.
- What are chances of getting COVID-19
after receiving a vaccine?
Well, you've got a better chance
of buying a winning lottery ticket
but it happened to Warriors player Damion Lee.
- [Reporter 1] He will be out at least two weeks.
It was not a false positive as first thought,
even though Walman had been vaccinated.
- [Reporter 2] Yankees GM Brian Cashman says
that three players tested positive
and three others are likely infected.
About 85% of the team is vaccinated,
including those who have the virus.
- [Narrator] These examples are known
as breakthrough infections,
which occur when someone tests positive
for COVID-19 at least two weeks after getting
their final shot.
Do these breakthrough cases mean the vaccines are failing?
- No, the vaccines are not failing.
The vaccines are working extremely well,
and as expected.
They do protect the majority of recipients
from severe disease.
- [Narrator] That's what vaccines are designed to do:
Prevent death and severe disease.
But most vaccines, including those created
to fight COVID-19
don't completely protect you from infection.
So it's not all that surprising
that breakthrough infections are showing up.
As of July 12th, more than 159 million people in the US
have been fully vaccinated.
CDC data suggests just under 5,500
have had breakthrough infections,
resulting in hospitalizations or deaths.
That's one in approximately 29,000 people
who have been vaccinated.
- Breakthrough infections are something
that we want to monitor
but in terms of their overall influence in the pandemic,
they play a much smaller role
than transmission among people who haven't been vaccinated.
- [Narrator] But these cases raise questions
about our immunity to the virus
and hint at a future in which it isn't gone completely
and we learn to live with it.
That's due in part to variants.
Research shows that variants,
including Delta, can partially evade the immune response
from prior infection and vaccination.
- We mount a really good immune response
against the virus that our body's trying to recognize.
Your body is really good
at recognizing and neutralizing those specific threats.
But when the virus starts to change,
sometimes it doesn't recognize the virus as well.
And so that's how you sort of see it chip away
at that immune response.
That's one of the reasons that health officials
are really sort of concerned
about this global vaccination drive
in order to prevent the virus from spreading,
both to save lives
and to prevent it from further mutating
and evading immune response.
- [Narrator] The Delta variant
is the most contagious version
of the virus to be identified,
but research suggests that full vaccination
is still protective against severe disease and death:
the outcomes that have made COVID-19 so devastating.
What dictates whether someone is more likely
to get infected, even if they're vaccinated?
Dr. Hatziioannou says there are four main variables.
First is the amount of virus that is circulating
in your community.
- So if a great number of people around you are infected,
then the possibility
of you getting exposed obviously increases.
If you're in close proximity with people
that are infected,
particularly those that are unvaccinated
and have generally higher viral loads,
then the probability of you getting infected increases.
- [Narrator] The second is tied to vaccine uptake.
- So if a large proportion of the population is vaccinated,
then your virus transmission,
virus loads, everything decreases.
So the chances of spreading the virus
amongst this population obviously decreases.
- [Narrator] That's because vaccinated people act
as a kind of shield,
even when they do get infected.
A recent CDC study found that vaccinated people
carried less virus and potentially didn't spread it
as much as unvaccinated people.
Cases were also shorter and less severe.
Vaccines help create a kind of immune memory
of what a virus looks like,
helping the body fight it off more quickly
when it spots it.
That makes it harder for the virus to spread overall.
Roughly half of all Americans are fully vaccinated
but in some states and globally,
the vaccination rate is much lower,
giving the virus more opportunity to spread and mutate.
That's why having large gathering,
like concerts or the Olympics can be so challenging
from a public health perspective.
Third, individual behavior matters.
- So as measures have been abandoned,
such as masking and social distancing,
when you don't have a significant number
of the population vaccinated,
then the ability of the vaccines to protect you
from getting infected decrease.
- [Narrator] Finally, even after vaccination,
individual immune systems vary in their ability
to prevent and fight off infection.
Older and immunocompromised people seem
to be more susceptible to breakthrough cases,
and those tend to be severe.
- That's why health officials
are considering additional doses right now,
primarily for people who have a compromised immune system
and might not have produced a good immune response
after two doses of the vaccine.
- [Narrator] Breakthrough cases might be asymptomatic
or mild, so people may not know to get tested.
But that's not the case for athletes.
- We're actually seeing breakthrough infections happen
a lot more amongst sports teams,
like baseball or for the Olympics
because those are the people
that get tested pretty regularly,
even if they're vaccinated.
- [Narrator] At the Olympics,
organizers of the games are scrambling
to deal with a rising load of athletes and officials
who are testing positive upon arrival in Japan,
some with breakthrough infections.
The vaccination rates are low in Japan.
Cases there are rising
and organizers didn't require those participating
to get vaccinated.
Dr. Hatziioannou and many other experts remain concerned
that holding a large-scale international event prior
to reaching a critical mass
of vaccinated individuals has the potential
to contribute to the virus's spread around the world.
- The Olympics is a special event
and it's truly remarkable
that it brings all these people
from all these different countries together
but it also poses a perfect ground
to mix variants and spread the virus
that will then go back to each athlete's country.