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Man: Pfizer only.
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If they try to give me Johnson & Johnson,
I'll tell them to give me COVID instead.
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Narrator: The internet seems to know
exactly which vaccines are the best
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and the worst.
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M: Moderna?
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More like mediocre, average.
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We don't do average.
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Mira Fricke: Humans love comparing.
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No wonder we're also doing it
with the COVID-19 vaccines.
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The problem is you can't
compare vaccines that easily.
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And doing so might even
be harmful in a pandemic.
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N: We tend to look at these numbers -
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efficacy rates -
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because they measure
how likely you are to get COVID-19
-
after you've been vaccinated.
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MF: The problem is that these numbers
were not created equal.
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Instead, they are determined by when
and where the efficacy trials took place.
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Carlos Guzmán: I think
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that simple comparisons
of vaccine efficacy out of context
-
can lead to very wrong conclusions.
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There are key differences
in the study population for example,
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age, gender, genetic environmental factor,
preexisting conditions.
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N: So how do efficacy trials work?
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Participants are split into two groups.
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One group gets the vaccine;
the other, a placebo.
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They then go about their lives as usual.
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After a certain period of time,
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researchers count
how many of them caught COVID-19.
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If all participants who got sick
came from the placebo group,
-
and zero from the vaccine group,
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the vaccine would be 100% effective.
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And if exactly the same number of people
from both groups got sick,
-
the vaccine efficacy would be zero
-
because the risk of getting infected
didn't change with the vaccine.
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But the chance of the participants
getting the disease during a trial
-
corresponds with the overall
infection rate in their environment.
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CG: There are also differences in terms
of presence or absence of virus variant
-
that are neutralized more
or less efficiently by the antibodies
-
stimulated by the type protein
of the original SARS‑CoV‑2 virus
-
that is the one that was included
in current vaccines.
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MF: So while we think
we know which vaccine is best,
-
our opinions have actually been influenced
by circumstantial factors.
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N: Let's look at an example.
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The Moderna and Pfizer trials
were performed mostly in the US
-
and before the arrival
of more infectious variants,
-
like the one from the UK or South Africa.
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The AstraZeneca or Johnson & Johnson
trials, on the other hand,
-
were either conducted later
-
or in countries
-
where more infectious variants emerged
and became dominant in infections.
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MF: So efficacy rates
will never be exactly the same
-
in a real world setting,
-
and they can change over time.
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CG: For example, recently we have
the report from Qatar,
-
where 50% and 45% of the infection
-
are caused by the South African
and the British variant.
-
This study showed us that the efficacy
of the BioNTech/Pfizer vaccine
-
drops to 89% and 75% for infection caused
by the British and South African variant.
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MF: But maybe there's been too much
fixation on effectiveness all along.
-
N: Effectiveness is usually the metric
for the best possible outcome:
-
no symptoms at all.
-
Instead, we could look at
-
how the vaccines prevent hospitalization
and death from COVID-19,
-
because all these vaccines
do that equally well.
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MF: Now there is one other aspect
that influences how we judge vaccines:
-
side effects.
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N: Reports of rare blood clots
have made headlines
-
and got people worried.
-
The EU also decided
not to renew its contracts
-
with AstraZeneca and Johnson & Johnson.
-
All this might give the impression
that some vaccines are worse than others.
-
MF: But again, it's not that simple
-
because everyone's individual risk
of getting infected
-
influences the assessment
of how beneficial each vaccine is.
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N: Let's look at an example
with the AstraZeneca vaccine
-
and assume moderate infection rates
of 55 cases per hundred thousand.
-
Out of 100,000 people under the age of 29,
-
around two will develop a rare blood clot
after the AstraZeneca vaccine,
-
but none would have needed intensive care
with a COVID-19 infection.
-
But someone over the age of 60
-
is much more likely to end up
in intensive care with COVID-19
-
and less likely to develop
a rare blood clot.
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MF: That's why some governments
recommend the AstraZeneca vaccine
-
only for people aged 60+.
-
But this assessment changes
if the infection rates are higher.
-
N: Let's look at the same calculation
but with higher infection rates.
-
Here, 401 cases per hundred thousand.
-
Now everyone is more likely to end up
in intensive care with COVID-19
-
than to develop a blood clot
after a vaccine.
-
In this scenario, the benefit
of getting the AstraZeneca vaccine
-
outweighs the risk of rare blood clots
for all age groups.
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CG: And of course,
-
for a preventive intervention aimed
at healthy individuals, like vaccine,
-
it is crucial
-
that the risk-benefit balance
-
is acceptable for different population,
groups or even individuals.
-
MF: So are some vaccines
worse than others?
-
If we just look at side effects,
-
some perform slightly better,
-
at least from what we know so far.
-
But that's only one aspect
-
and shouldn't be the only one we consider.
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CG: I think that the key issue
-
is that the best vaccine
or vaccination program
-
is the one that allows us
to prevent disease and death.
-
And of course, to reduce the direct
and indirect consequences -
-
negative consequences -
-
on the bad damage.
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MF: Any vaccine that received
emergency approval from the WHO
-
protects against severe cases of COVID-19.
-
They prevent deaths
and help end this pandemic.
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N: So as long as vaccines are scarce,
-
there's a pretty good argument
to take whichever one is available to us,
-
because if we insist
on getting a specific vaccine,
-
we might prolong this entire pandemic,
-
and that can cost lives.
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Subtitles by Maurício Kakuei Tanaka
Review by Carol Wang