J&J Vaccine Clot Issue Shows Limits of Clinical Trials, Scientists Say
By Thomas M. Burton
WASHINGTON -- Clinical trials are medicine's way of deciding
whether vaccines and drugs work, and how safe they are.
But the studies have limits, as was shown Tuesday when U.S.
health authorities called for temporarily sidelining Johnson &
Johnson's Covid-19 vaccine while they investigate blood clots that
six women developed after getting the shot.
The Food and Drug Administration approved an emergency use
authorization for the J&J vaccine following positive results in
clinical trials involving 44,000 people, half of whom got the
vaccine, with the rest getting a placebo.
Since then, nearly seven million people in the U.S. have gotten
the J&J shot. Scientists say it isn't surprising that other
side effects occurred as the vaccine was given to a much larger
population than during trials.
"We have to keep reiterating that we can't pick up a
one-in-a-million event in clinical trials," said Arnold Monto, a
University of Michigan epidemiologist and public-health professor
who chairs the independent panel that evaluated the J&J
clinical study for the Food and Drug Administration.
Paul Offit, a vaccine authority and pediatrics professor at the
Children's Hospital of Philadelphia, agreed that a trial of 44,000
people would be "unlikely to pick up an instance of adverse events
at the rate of one in a million."
Both Dr. Offit and Dr. Monto noted that the cases of blood clots
did turn up in the FDA's post-study safety net once vaccination
commenced in the broader population.
Dr. Offit said he thinks the phenomenon of cerebral blood clots
among younger women linked to the Covid-19 J&J vaccine is real,
although rare, and added that federal officials were wise to pause
the use of the vaccine.
Even beneficial vaccines can have side effects -- for example,
flu vaccines have been linked to possibly causing rare cases of
Guillain-Barre syndrome, a rare neurological disorder.
The oral polio vaccine, now largely discontinued, led to one
polio case in about 2.4 million doses -- a ratio considered
acceptable given how many cases it prevented.
Write to Thomas M. Burton at firstname.lastname@example.org
(END) Dow Jones Newswires
April 13, 2021 14:57 ET (18:57 GMT)
Copyright (c) 2021 Dow Jones & Company, Inc.