Man: Pfizer only.
If they try to give me Johnson & Johnson, I'll tell them to give me COVID instead.
Narrator: The internet seems to know exactly which vaccines are the best
and the worst.
M: Moderna?
More like mediocre, average.
We don't do average.
Mira Fricke: Humans love comparing.
No wonder we're also doing it with the COVID-19 vaccines.
The problem is you can't compare vaccines that easily.
And doing so might even be harmful in a pandemic.
N: We tend to look at these numbers -
efficacy rates -
because they measure how likely you are to get COVID-19
after you've been vaccinated.
MF: The problem is that these numbers were not created equal.
Instead, they are determined by when and where the efficacy trials took place.
Carlos Guzmán: I think
that simple comparisons of vaccine efficacy out of context
can lead to very wrong conclusions.
There are key differences in the study population for example,
age, gender, genetic environmental factor, preexisting conditions.
N: So how do efficacy trials work?
Participants are split into two groups.
One group gets the vaccine; the other, a placebo.
They then go about their lives as usual.
After a certain period of time,
researchers count how many of them caught COVID-19.
If all participants who got sick came from the placebo group,
and zero from the vaccine group,
the vaccine would be 100% effective.
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.
But the chance of the participants getting the disease during a trial
corresponds with the overall infection rate in their environment.
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.
MF: So while we think we know which vaccine is best,
our opinions have actually been influenced by circumstantial factors.
N: Let's look at an example.
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.
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.
MF: So efficacy rates will never be exactly the same
in a real world setting,
and they can change over time.
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.
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.
MF: Now there is one other aspect that influences how we judge vaccines:
side effects.
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.
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.
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.
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.
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.
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.
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.
Subtitles by Maurício Kakuei Tanaka Review by Carol Wang