By Peter Loftus
Infectious-disease specialists are working to reassure people
that they are still getting protection from Covid-19 vaccines, even
if they don't experience the flulike side effects that hit some
people after vaccination.
Fatigue, chills and other symptoms in the days following
vaccination are evidence that the vaccine is having the desired
effect on the body's immune system, according to public health
officials. The U.S. Centers for Disease Control and Prevention and
the World Health Organization say on their websites that side
effects mean the body is "building protection" against the
That message may lead some people to infer that the absence of
side effects indicates that vaccination isn't causing the body to
build immunity to the virus. Yet infectious-disease doctors say
most people get protection from the vaccines, even if they don't
experience side effects.
"I don't think someone should correlate the extent of their
reactions to the vaccine with protection from infection," said H.
Cody Meissner, chief of the pediatric infectious diseases division
at Tufts University School of Medicine in Boston. "We know that
people who don't respond to a vaccine in terms of the side effects
still are well protected. The vaccines work even if you don't have
fatigue and headache and fever and muscle pain and joint pain."
Experts say more research is needed to establish what
vaccine-related side effects, or their absence, tell us about the
strength of people's immune responses. "There are just so many
nuances in terms of how you respond," said Kathryn Edwards,
professor of pediatrics and a vaccine researcher at Vanderbilt
University School of Medicine in Nashville, Tenn.
Dr. Edwards said there is a biological basis to tell people
"it's good to feel bad" because side effects can be a sign of an
immune response. But, she added, "I think we should have
confirmation there is a relationship." She said she has fielded
questions from vaccine recipients who didn't experience side
effects and worried that the absence meant they weren't getting
Vaccines against other diseases have been known to cause side
effects because the immune response releases inflammatory
substances in the body.
A small study conducted recently by scientists at the University
of Pennsylvania found that people who had more robust side effects
after receiving either of the two leading vaccines in the U.S. --
from Pfizer Inc./ BioNTech SE and Moderna Inc. -- had slightly
higher antibody levels than those who had less robust side effects.
Yet all people getting the vaccine in the study had good immune
responses, said study co-author E. John Wherry, director of the
Penn Institute for Immunology.
The Pfizer and Moderna vaccines use RNA-based technology and can
cause similar side effects. Ranging from injection-site pain,
fatigue, headache, muscle pain, joint pain, in addition to fever
and chills, these typically arise within a day of vaccination and
resolve within a couple of days. The side effects can often be
managed by taking acetaminophen or another pain reliever.
The vaccines were at least 94% effective at protecting against
Covid-19 in separate, large clinical trials that started last
Injection-site pain or swelling is the most common reaction,
occurring in 92% of Moderna vaccine recipients and 84% of those
getting the Pfizer shot, the studies found.
A Pfizer spokeswoman said side effects don't indicate the level
of immunity conferred by its vaccine. It wouldn't be able to
demonstrate such high efficacy, if the only people protected were
the ones with symptoms, she said.
Moderna didn't immediately reply to a request for comment.
Johnson & Johnson's one-shot Covid-19 vaccine uses a
different technology than the Pfizer and Moderna shots. A large
study found that injection-site pain affected about 49% of
recipients, while headache, fatigue or muscle ache occurred at
lower rates. A small number of J&J vaccine recipients have
developed serious blood clots.
Age appears to be a factor in determining who experiences side
effects. People over age 65 are less likely than younger people to
experience side effects. Older adults tend to have less robust
immune responses to vaccines.
Vanderbilt's Dr. Edwards said women appear to be more likely
than men to experience the side effects, which may be related to
hormonal or weight differences.
The Food and Drug Administration says age, sex and general
health likely influence the occurrence and severity of common side
effects in the first couple of days after vaccination. Side effects
don't correlate with the effectiveness of a vaccine in an
individual, an FDA spokeswoman said.
Some doctors say heredity may also play a role. "I am sure that
our genes at some level determine differences in these responses,"
Paul Offit, director of the vaccine education center at Children's
Hospital of Philadelphia, said of varying levels of symptoms
For some receiving the RNA vaccines, side effects are more
pronounced after the second dose, making it hard for people to work
or be active. In contrast, people who were previously infected with
the coronavirus have had more pronounced side effects after the
first dose, Dr. Edwards said.
Major Hayden, a 38-year-old software developer living near San
Antonio, said he began feeling chills, fatigue and fever several
hours after getting the second dose of Moderna's vaccine in early
May. He took acetaminophen and began to feel better the following
"For me it just seemed like the risks from the vaccine were much
smaller than the risks of Covid," he said.
Write to Peter Loftus at firstname.lastname@example.org
(END) Dow Jones Newswires
May 17, 2021 05:44 ET (09:44 GMT)
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