By Peter Loftus
Johnson & Johnson's Covid-19 vaccine was authorized for use
in the U.S. by federal health regulators in late February.
Authorities on April 13 recommended pausing its use to investigate
rare but severe cases of blood clots.
It was the third shot to be cleared after vaccines from Pfizer
Inc. and its partner BioNTech SE and from Moderna Inc. And it was
the first shot requiring just one dose, rather than two. Here's
what we know and don't know:
Why is the J&J vaccine being paused?
U.S. health authorities are investigating six reported cases of
blood clots, including one death. Six women, ages 18 to 48 years,
were reported to have experienced the clots as well as low levels
of platelets, which help with clotting. The cases were extremely
rare -- more than 6.8 million doses of the shot have been given in
the U.S. so far -- but the U.S. Food and Drug Administration said
it was making the recommendation out of an abundance of
How do the three Covid-19 vaccines compare?
They all work well at preventing the Covid-19 disease, health
experts say. The Pfizer-BioNTech and Moderna shots were more than
94% effective at preventing Covid-19 in their late-stage trials,
while J&J's effectiveness was 66%. But the difference may be
less than it seems. The Pfizer-BioNTech and Moderna shots were
tested before the emergence of strains like one first identified in
South Africa, which various studies have indicated eludes vaccines
somewhat, though they still work against it. J&J's vaccine was
tested in South Africa, and its effectiveness wasn't as high there
as in other countries, hurting the vaccine's overall effectiveness.
The J&J vaccine was 72% effective in the U.S. portion of its
Yet health experts say J&J's vaccine is plenty effective.
Importantly, it was 85% effective against severe Covid-19 at least
28 days after vaccination. That suggests the vaccine should help
many people avoid the kinds of serious cases that result in
hospitalization and death.
Which Covid-19 vaccine should I get?
Health authorities have generally said people should take the
first vaccine they can get because early supplies have been
constrained. But if you do have a choice, there are some key
differences that could guide your decision. J&J's vaccine is
given as a single dose, which may be a more convenient option than
the two doses required for both of the Pfizer-BioNTech and Moderna
vaccines, given three or four weeks apart. Only the Pfizer-BioNTech
vaccine is authorized for adolescents 16 and 17 years old, while
J&J and Moderna's shots are cleared for those 18 and older.
The U.S. Food and Drug Administration says people who are
allergic to the ingredients of a vaccine shouldn't take it. The
vaccines from Pfizer and Moderna contain, among other ingredients,
the genetic material RNA and a substance called polyethylene
glycol, which has been associated with rare allergic reactions. The
J&J vaccine contains an adenovirus, a virus that can cause the
common cold, which is rendered harmless; polysorbate and other
A healthy, younger woman with a history of an allergic reaction
known as anaphylaxis may opt for J&J's vaccine because there
appears to be a lower rate of such side effects than seen for the
vaccines from Pfizer and Moderna, said Dr. Gregory Poland, a Mayo
Clinic vaccine researcher and fellow with the Infectious Diseases
Society of America. Conversely, a 65-year-old man with a blood type
associated with higher risk of severe Covid-19 may opt for a Pfizer
or Moderna vaccine because of the strong evidence of efficacy in
both clinical trials and real-world use, he said.
When can I get J&J's shot?
How effective is J&J's Covid-19 vaccine?
It appears to work well. The vaccine's 66% effectiveness rate
shows it can protect a majority of most vaccinated adults from
moderate to severe Covid-19, the disease caused by the coronavirus.
And the vaccine was even more effective preventing severe disease
specifically, posting the 85% rate. By comparison, an annual flu
shot is considered to work well if it is 60% effective.
What are the side effects of J&J's vaccine?
The most common side effects among people who received the
vaccine were injection-site pain, headache and fatigue. Most were
mild to moderate. J&J has received preliminary reports of two
cases of severe allergic reactions in vaccine recipients, one of
which was anaphylaxis. Now, health authorities are investigating
the blood clots. A panel of outside experts will meet Wednesday to
review the matter for the CDC, while the FDA will also conduct an
How was J&J's Covid-19 vaccine tested?
Starting in September, J&J enrolled more than 44,000 adults
in the U.S. and several other countries including Brazil and South
Africa in a clinical trial. The subjects received a single dose of
either the vaccine or a placebo. Researchers counted how many
people subsequently contracted moderate to severe Covid-19 starting
14 days after vaccination, until a certain number of people fell
ill. Researchers then examined whether there were fewer vaccinated
people than unvaccinated people among the Covid-19 cases.
Researchers also monitored for side effects among the study
How does J&J's vaccine work?
The vaccine uses a harmless type of virus, called an adenovirus,
which can cause cold symptoms. It is modified to contain the DNA of
the so-called spike protein found on the surface of the new
coronavirus. After injection, the cold-virus vector carries the DNA
payload into human cells. Once inside the cells, the DNA payload
causes the production of the spike protein. This, in turn, triggers
an immune response that can later defend against the real
coronavirus if a vaccinated person is exposed to it.
What don't we know about J&J's Covid-19 vaccine?
We don't know its safety and effectiveness in children, or among
pregnant women, their fetuses or women nursing babies. We also
don't know how long vaccine-induced protection will last. The
company has started a study testing the vaccine in adolescents and
is conducting a separate study testing whether adding a second dose
improves its performance. Also uncertain is whether the vaccine can
help curb the spread of the virus by infected people who don't have
symptoms, a group that turns out to be responsible for a lot of
transmission. A preliminary analysis by J&J gave tantalizing
signs the company's vaccine could limit asymptomatic spread, by
reducing infections that didn't cause symptoms in study subjects.
Health authorities are also probing the clotting issue.
Does J&J's vaccine protect against new coronavirus
The vaccine was less effective in South Africa and Latin America
than in the U.S. That could be a sign the vaccine is less
protective against strains circulating in those regions, though
J&J is still conducting that analysis. J&J's vaccine was
57% effective in South Africa and 66% in Latin America, compared
with 72% in the U.S. during the late-stage trial, according to
J&J. Even at the lower levels of effectiveness in South Africa
and Latin America, health experts say, J&J's vaccine works
well. The company said it is working on a version of the vaccine
targeting the variant first identified in South Africa. Even in
study subjects there, the shot still performed above what health
experts say is needed to protect many people and provide the
community immunity needed to move to a post-pandemic life.
Have there been production problems with the J&J
In late March, J&J said a batch of the main ingredient for
its vaccine that was manufactured at a contractor's plant in
Baltimore didn't meet quality standards. But no finished doses from
the batch were distributed, and the contractor, Emergent
BioSolutions Inc., plans to dispose of the batch. J&J says it
still expects to meet its supply commitments for the vaccine.
Write to Peter Loftus at email@example.com
(END) Dow Jones Newswires
April 13, 2021 14:18 ET (18:18 GMT)
Copyright (c) 2021 Dow Jones & Company, Inc.