The One Vaccine Efficacy Number that Truly Matters
Shopping for the best Covid-19 vaccine? Here’s something to
keep in mind.
By Faye Flam
March 6, 2021, 1:00 PM GMT
Something sounds
fishy when public health experts advise us to take whatever vaccine is
available even though some vaccines show much more promising efficacy numbers
than others. And it’s understandable that people would want to shop for the
best vaccine. Americans are accustomed to the idea of consumer choice in
pharmaceuticals — why else would we have so much direct-to-consumer drug
advertising? But cut through the noise and there’s only one thing that really
matters: all three FDA-authorized vaccines seem to work equally well — close
to 100% — at preventing hospitalization and death.
That message has gotten diluted in the reporting around the
efficacy numbers for different vaccines. The efficacy numbers associated with
the Moderna and Pfizer vaccines came
in at around 95%,
while the newly approved Johnson &
Johnson vaccine has shown a less impressive 72% in the U.S., and even lower
in other countries. As risk communication expert Peter Sandman says, people
remember from school that 95% usually earns and A, and 72% a C at best.
The problem is that numbers most touted to measure “efficacy” measure various degrees of
symptoms plus a positive test — criteria that vary some from trial to
trial. They don’t measure what’s most important: protection against hospitalization and
death.
And on that score, all three vaccines are outstanding. So public
health experts are justified in suggesting people take the first vaccine
available.
People aren’t only worried about dying from Covid; they’re
also worried about getting so-called long Covid and transmitting the disease to others
even after they’re vaccinated. There’s no data one way or the other one
whether vaccination cuts the risk of long Covid for those who get sick, but
all the vaccines appear to reduce the number of people who get mild
illness or asymptomatic cases, and thereby probably reduce transmission.
While the Pfizer and Moderna vaccines work the same way,
Johnson & Johnson’s vaccine works through a different mechanism. The first
two use messenger RNA, and the latter uses DNA, which is ferried to the
nucleus of cells with a different kind of virus, called an adenovirus, modified
so it can’t replicate itself and cause disease. All three vaccines have good safety data, and all of them prompt
the body to produce T-cells, which retain a sort of memory of the protein and attack
it.
One reason for the seemingly stark difference in efficacy
numbers is that the clinical trials
were held in very different groups of people. The Johnson & Johnson trial enrolled more people with
hypertension, diabetes and HIV, as well as more people over 60, says
University of California infectious disease doctor Monica Gandhi. Johnson and
Johnson’s results also came from testing people in South Africa and Latin
America at a time when new variants of the virus were already
rampant. The important thing to note, says Gandhi, is that nobody who
got the vaccine in the clinical trials — for any of the shots — was
hospitalized for Covid-19. None of them died. None even got a severe enough
case to require medical intervention at all.
The absence of hospitalizations and deaths in the Johnson
and Johnson trial looks even more impressive given that the volunteers included
people who were more vulnerable to dying from the virus. Gandhi says she’d
advise her own 80-something parents to get that shot if it was the first one
available.
Earlier this year, Yale University epidemiologist Robert
Hecht had told me in an interview that he thought more lives could be saved by
vaccinating people in so-called hot spots where there was an unusually high
burden of disease. I called him back and asked whether the single-shot advantage of the Johnson and Johnson vaccine might
make it a good choice for those places. He agreed it would, but worried about
the perception that it’s an inferior vaccine, which could incite outrage
about racial or socioeconomic injustice.
Other experts are also wrestling with this question, since
the Johnson & Johnson vaccine is cheaper than the other approved shots,
delivered in a single dose, and requires only ordinary refrigeration rather
than ultra-cold storage. That would make it a practical choice for vaccinating
homeless people, and those in hard-to-reach rural areas, but again, experts are
wrestling with the perception of inequality.
That concern isn’t justified, given a proper interpretation
of the data. Even the perception of unfairness, though, could be harmful.
Giving people the ability to vaccine-shop might help more hesitant people feel
more in control and less coerced — but also inadvertently prolong the pandemic.
Getting the one-shot vaccine out as fast as possible and
focusing on virus hot spots would save lives and hasten a return to some
level of normal life. It’s now up to the public health community to send out a
clearer message and get the public on board.
The most important numbers here aren't 95% or 72%, but 0%: the number of
vaccinated people who've died from the virus. When that's the
emphasis, the message to get the first available vaccine makes a lot more
sense.
This column does not necessarily reflect the opinion of the
editorial board or Bloomberg LP and its owners.
To contact the author of this story:
Faye Flam at fflam1@bloomberg.net
To contact the editor responsible for this story:
Sarah Green Carmichael at sgreencarmic@bloomberg.net
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