- [Narrator] Schools used to look like this,

classrooms packed with students,

lunchrooms full of loud conversations,

and teachers just trying to catch a break in the lounge.

It's a scene that now looks prime

for the spread of the coronavirus.

- You have a lot of people together

in one space for a long period of time

without masks.

We don't know if the ventilation's any good,

and with activities like shouting,

those are all the ingredients for a super-spreading event.

- [Narrator] That's why now, school looks very different.

Many schools are only partially open for in-person learning,

and others are still fully remote.

- It's not business as usual,

everything has changed.

- [Narrator] Elia Valdes has been back

in her classroom since October.

- I was very concerned about health issues.

I knew that this was the best thing for students,

to go in physically, 'cause that's hands-down,

they will always perform better.

- [Narrator] With the virus still spreading,

can schools reopen safely?

What are the risks of catching COVID there,

and how do control measures,

like wearing a mask or increasing ventilation

change that picture?

Let's look at the classroom, lunchroom, and break room.

- Classrooms are one place where you have

a lot of people in the room for a long period of time,

that's pretty risky.

- [Narrator] This is particularly true

for adults or older kids.

- Age really matters in terms of transmission,

both in terms of acquisition of COVID,

as well as transmission of SARS-CoV-2,

the virus that causes COVID.

- [Narrator] Studies have found,

that compared with adults,

children might be infected less often,

are less likely to show severe symptoms,

and are less likely to be hospitalized

for severe infection.

That said, the risk isn't zero, even for younger kids.

We know that the virus is transmitted

in a variety of ways.

Large droplets exchanged in a close range,

small droplets lingering in the air,

and indirectly through contact with a contaminated surface.

- If somebody who is infected with COVID

comes into a classroom

and there's no control measures in place,

then they're sitting there breathing and talking,

and they're releasing virus into the air.

- [Narrator] Think of the virus forming a small cloud

in front of the infected person.

Larger, virus-laden droplets

expelled from the nose or mouth,

would fall nearby, while the smaller droplets

would float further away,

and that's just from talking normally.

- By shouting and screaming and being emotional,

you can give these droplets superpowers,

make them smaller, which we call aerosol,

and can fly further, 10, 20 feet in some cases.

- It's gonna kinda fill the room eventually,

especially if that room is poorly ventilated,

and then everyone else in that room

is going to be exposed to it,

and they'll be forced to breathe it.

- [Narrator] But this picture changes dramatically

when control measures are put in place.

Experts say the most important one is masking.

With masks on everyone, the infected person

would release less virus into the air.

And the others would have some protection

against the virus that remains.

- I would say the second most important thing

is to ensure good ventilation of the classroom.

It could be as simple as opening some doors and windows.

- [Narrator] Doing so helps replace

the air inside the classroom,

bringing in clean air from outside.

That can remove or reduce the virus in the room,

lowering the risk of transmission.

Physical distancing is another way to mitigate risk.

The CDC used to recommend six feet,

but it's since changed it to three.

- There's not a magic number for safe versus unsafe,

but the farther apart people are, the better,

so that they're kind of out

of each other's directly exhaled breath.

- [Narrator] A study of Massachusetts Public Schools

found that case rates

in schools maintaining three feet of distance

were similar to those of schools using six feet.

Prevention gets more complicated in the lunchroom.

- So in the lunchroom setting, it's virus heaven.

The virus is in paradise because they have so many ways

to infect noses and mouths.

- [Narrator] That's because to eat,

students need to take off their masks,

taking away a key control measure.

To compensate, experts recommend

adding portable air cleaners

with HEPA filters, if possible.

- The portable air cleaner works

by pulling air through it and passing it through

a really high quality filter

that filters out and removes all the aerosols

that are in the air and all the virus

that they might contain.

And then out the other side of the portable air cleaner

comes nice, clean, virus-free air.

- [Narrator] In the teacher break room,

cleaning the air is also really important,

because it's only adults.

- Adults, of course, breathe more than kids do

and produce probably even per breath,

produce more aerosols.

And so let's say someone's sick,

well an adult is probably gonna release more virus

into the air, and the other adults in that room

are gonna be breathing more of that air compared to kids.

- [Narrator] Surface cleaning

and hand-washing are all important here,

just maybe not as critical as was initially thought.

- Excessive attention to surface cleaning

is taking away time and energy

from cleaning the air, which is gonna be more important

for reducing the risk of transmission in schools.

- [Narrator] For teachers, vaccination

is the latest control measure, and most states

are giving K through 12 educators priority.

- I just recently got my vaccine,

so that makes me feel a lot better.

- [Narrator] Even with a vaccine,

limiting teacher interactions with students is important.

- What can you do?

- [Narrator] Because it's still unclear

if vaccination stops transmission.

And studies have shown adults are more likely

to transmit the virus than younger kids,

for whom vaccines aren't authorized yet.

- I would always greet my students at the door.

Hello, how are you, come on in.

Sit down, some of them would give me hugs.

Oh, Miss Valdes, high five.

Now it's like elbow or nope, social distance, remember,

we can't get close to one another.

- [Narrator] Experts say the key is not relying

on any one control strategy.

Masking, distancing, ventilation, vaccination,

and testing all have a role to play

in how schools reopen.

- So to try and keep everything all at once,

and that laundry list in place,

it's probably going to be very frustrating for many people.

And I think if you had to do one thing,

it's probably going to be wearing that mask.

(uplifting music)