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This is the new one-dose Covid-19 vaccine
from Johnson & Johnson.

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In early March,
more than 6,000 doses

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were supposed to be shipped
to the city of Detroit, Michigan

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but the mayor said, "No thanks".

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"Moderna and Pfizer are the best.

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And I am going to do
everything I can

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to make sure the residents
of the city of Detroit get the best."

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He was referring to these numbers:
the vaccines’ "efficacy rates."

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The vaccines from Pfizer/BioNTech
and Moderna

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have super high efficacy rates:

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95% and 94%.

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But Johnson & Johnson?

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Just 66%.

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And if you only look at these numbers,
it’s natural to think that these vaccines

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are worse than these.

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But that assumption is wrong.

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These numbers are arguably
not even the most important measure

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of how effective these vaccines are.

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To understand what is,

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you first have to understand
what vaccines are even supposed to do.

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A vaccine’s efficacy rate
is calculated in large clinical trials,

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when the vaccine is tested
on tens of thousands of people.

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Those people are broken into two groups:

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half get the vaccine,
and half get a placebo.

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Then, they’re sent out
to live their lives,

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while scientists monitor whether or not
they get Covid-19 over several months.

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In the trial for Pfizer/BioNTech, for
example, there were 43,000 participants.

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In the end, 170 people
were infected with Covid-19.

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And how those people fall 
into each of these groups

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determines a vaccine’s efficacy.

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If the 170 were evenly split,

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that would mean you’re just as likely
to get sick with the vaccine

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as without it.

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So it would have a 0% efficacy.

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If all 170 were in the placebo group, and
zero people who got the vaccine were sick,

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the vaccine would have
an efficacy of 100%.

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With this particular trial,
there were 162 in the placebo group,

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and just eight
in the vaccine group.

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It means those who had the vaccine
were 95% less likely to get Covid-19:

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The vaccine had a 95% efficacy.

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Now, this doesn’t mean that if 100 people
are vaccinated, 5 of them will get sick.

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Instead, that 95% number
applies to the individual.

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So each vaccinated person

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is 95% less likely than a person 
without a vaccine to get sick

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each time they’re exposed to Covid-19.

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And every vaccine’s efficacy rate
is calculated in the same way.

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But each vaccine’s trial might be done in
very different circumstances.

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So, one of the biggest 
considerations here,

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when we look at these numbers,

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is the timing in which
these clinical trials were performed.

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This is the number of daily Covid-19 cases
in the US since the pandemic began.

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The Moderna trial was done
completely in the US, here, in the summer.

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The Pfizer/BioNTech trial was primarily
based in the US, too,

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and at the same time.

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Johnson & Johnson, however,
held their US trial at this time,

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when there were more opportunities

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for participants 
to be exposed to infections.

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And most of their trial took place 
in other countries,

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primarily South Africa and Brazil.

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And in these other countries,
not only were case rates high,

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but the virus itself was different.

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The trials took place
as variants of Covid-19 emerged,

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and became the dominant infections
in these countries;

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variants that are more likely 
to get participants sick.

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In South Africa, most of the cases in the
Johnson & Johnson trial were that of the

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variant, not the original strain that was
in the US over the summer.

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And despite that, it still
significantly reduced infections.

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"If you're trying to make one-to-one 
comparisons between vaccines,

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they must have been studied in the same
trial, with identical inclusion criteria,

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in the same parts of the world,
at the same time."

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"If we were to take
Pfizer and Moderna's vaccines and

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redo their clinical trial at the same time
that we saw J&J's clinical trial,

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we might see quite different
efficacy numbers for those."

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These efficacy numbers just tell you
what happened in each vaccine’s trial,

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not exactly what will happen
in the real world.

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But many experts argue this isn’t even the
best number to judge a vaccine by anyway.

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Because preventing any infection at all is
not always the point of a vaccine.

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"The goal of a Covid-19 vaccine program
is not really to get to 'Covid zero',

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

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to remove its ability to cause serious
disease, hospitalization, and death."

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It helps to look at the different outcomes
of an exposure to Covid-19 like this:

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The best-case scenario
is, you don’t get sick at all.

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The worst case is death.

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In between, there’s being hospitalized,
severe-to-moderate symptoms,

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or having no symptoms at all.

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In the best circumstances, vaccines
give you protection all the way to here.

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But realistically, that isn’t the
main objective of Covid-19 vaccines.

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The real purpose is to give your body the
protection to cover these possibilities,

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so if you do get an infection,
it feels more like a cold

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than something you'd be
hospitalized for.

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And this is one thing that every one
of these Covid-19 vaccines do well.

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In all these trials, while some people in
the placebo groups were hospitalized,

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or even died from Covid-19,

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not one fully vaccinated person,
in any of these trials,

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was hospitalized or died from Covid-19.

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"Something I wish that mayor
would have understood

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was that all three vaccines are basically
100% effective in protecting from death."

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The mayor of Detroit backtracked and said
he’d start taking Johnson & Johnson doses,

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because it’s still "highly effective
against what we care about most."

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Efficacy matters.
But it doesn’t matter the most.

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The question isn’t which vaccine will
protect you from any Covid infection,

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but which one will keep you alive?

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Or out of the hospital?

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Which one will help end the pandemic?

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And that’s any of them.

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"The best vaccine right now for you
is the one that you're offered."

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"With each shot given to someone,
we approach the end of this pandemic."