Why you can't compare Covid-19 vaccines (Subtitles)

This is the new one-dose Covid-19 vaccine

from Johnson & Johnson.

In early March,

more than 6,000 doses

were supposed to be shipped

to the city of Detroit, Michigan.

But the mayor said, no thanks.

"Moderna and Pfizer are the best.

And I am going to do

everything I can

to make sure the residents

of the city of Detroit get the best."

He was referring to these numbers:

the vaccines’ "efficacy rates."

The vaccines from Pfizer/BioNTech

and Moderna have super high efficacy rates:

95 and 94 percent.

But Johnson & Johnson?

Just 66%.

And if you only look at these numbers,

it’s natural to think that these vaccines

are worse than these.

But that assumption is wrong.

These numbers are arguably

not even the most important measure

of how effective

these vaccines are.

To understand what is, you first have to understand

what vaccines are even supposed to do.

A vaccine’s efficacy rate

is calculated in large clinical trials,

when the vaccine is tested

on tens of thousands of people.

Those people are broken into two groups:

half get the vaccine,

and half get a placebo.

Then, they’re sent out

to live their lives,

while scientists monitor whether or not

they get Covid-19 over several months.

In the trial for Pfizer/BioNTech, for

example, there were 43,000 participants.

In the end, 170 people

were infected with Covid-19.

And how those people fall into each of these

groups determines a vaccine’s efficacy.

If the 170 were evenly split,

that would mean you’re just as likely

to get sick with the vaccine as without it.

So it would have a 0% efficacy.

If all 170 were in the placebo group, and

zero people who got the vaccine were sick,

the vaccine would have

an efficacy of 100%.

With this particular trial,

there were 162 in the placebo group,

and just eight

in the vaccine group.

It means those who had the vaccine

were 95% less likely to get Covid-19:

The vaccine had a 95% efficacy.

Now, this doesn’t mean that if 100 people

are vaccinated, 5 of them will get sick.

Instead, that 95% number

applies to the individual.

So, each vaccinated person is 95% less likely

than a person without a vaccine

to get sick, each time

they’re exposed to Covid-19.

And every vaccine’s efficacy rate

is calculated in the same way.

But each vaccine’s trial might be done in

very different circumstances.

"So, one of the biggest considerations here,

when we look at these numbers,

is the timing in which

these clinical trials were performed."

This is the number of daily Covid-19 cases

in the US since the pandemic began.

The Moderna trial was done

completely in the US, here, in the summer.

The Pfizer/BioNTech trial was primarily

based in the US, too, and at the same time.

Johnson & Johnson, however,

held their US trial at this time,

when there were more opportunities

for participants to be exposed to infections.

And most of their trial took place in other

countries, primarily South Africa and Brazil.

And in these other countries,

not only were case rates high,

but the virus itself

was different.

The trials took place

as variants of Covid-19 emerged,

and became the dominant infections

in these countries;

variants that are more likely

to get participants sick.

In South Africa, most of the cases in the

Johnson & Johnson trial were that of the variant,

not the original strain that was

in the US over the summer.

And despite that, it still

significantly reduced infections.

"If you're trying to make one-to-one,

head-to-head comparisons between vaccines,

they need to have been studied in the

same trial, with the same inclusion criteria,

in the same parts of the world,

at the same time."

"If we were to take

Pfizer and Moderna's vaccines,

and redo their clinical trial at the same time

that we saw J&J's clinical trial,

we might see quite different

efficacy numbers for those."

These efficacy numbers really just tell you

what happened in each vaccine’s trial,

not exactly what will happen in the real world.

But many experts argue this isn’t even the

best number to judge a vaccine by anyway.

Because preventing any infection at all is

not always the point of a vaccine.

"The goal of a vaccine program for Covid-19

is not necessarily to get to 'Covid zero,'

but it's to tame this virus, to defang it,

to remove its ability to cause

serious disease, hospitalization, and death."

It helps to look at the different outcomes

of an exposure to Covid-19 like this:

The best-case scenario

is, you don’t get sick at all.

The worst case is death.

In between, there’s being hospitalized,

severe-to-moderate symptoms,

or having no symptoms at all.

In the absolute best circumstances, vaccines

give you protection all the way to here.

But realistically, that isn’t the

main objective of Covid-19 vaccines.

The real purpose is to give your body enough

protection to cover these possibilities,

so if you do get an infection,

it feels more like a cold

than something you'd be

hospitalized for.

And this is one thing that every one

of these Covid-19 vaccines do well.

In all these trials, while some people in

the placebo groups were hospitalized,

or even died from Covid-19,

not one fully vaccinated person,

in any of these trials,

was hospitalized or died from Covid-19.

"One thing that I wish that mayor

would have understood,

was that all three vaccines have essentially

100% effectiveness in protecting from death."

The mayor of Detroit did backtrack, and said

he’d start taking Johnson & Johnson doses,

because it’s still "highly effective against

what we care about most."

Efficacy matters. But it doesn’t matter the most. The question isn’t which vaccine will protect you from any Covid infection, but which one will keep you alive? Or out of the hospital? Which one will help end the pandemic?

And that’s any of them. "The best vaccine right now for you is the one that you're offered." "With each shot that goes into someone's arm, we get closer to the end of this pandemic."