Does Getting the Covid-19 Vaccine Stop You Spreading It? Scientists Don't Know Yet.
By WSJ Noted.
The Covid-19 vaccines authorized in the U.S. are approximately
95% effective at preventing people from getting sick with symptoms,
according to Pfizer and Moderna, the companies that produce them.
But scientists are still studying whether vaccination prevents
transmission to others.
1. There is not enough evidence yet on whether the vaccines
prevent asymptomatic infection.
Some research suggests that, without vaccines, roughly a quarter
of Covid-19 transmissions result from asymptomatic spread. There is
some indication that vaccination may reduce asymptomatic infection,
resulting in reduced transmission. Preliminary evidence from
Moderna showed that participants in a clinical trial who received
the vaccine and were tested for Covid between their first and
second doses had a roughly two-thirds reduction in asymptomatic
infections. But experts note the data set was small and more
results are needed.
2. Precautions will be necessary until the U.S. gets closer to
herd immunity, experts say.
Wearing masks, social distancing and avoiding crowded spaces are
likely to be necessary for some time, experts say. Marion Pepper,
an immunologist and associate professor at the University of
Washington in Seattle says that even after getting vaccinated, if
someone is exposed to the virus it can take the body's immune
response some time to control an infection and the potential for
transmission depends on how quickly the infection is controlled.
"Most vaccines prevent disease as opposed to preventing infection,"
says Anna Durbin, a professor of international health at Johns
Hopkins Bloomberg School of Public Health who is working on the
AstraZeneca Covid-19 vaccine trial and previously worked on the
Pfizer vaccine trial. She believes Covid vaccine studies will
eventually show a reduction in asymptomatic transmission but not a
3. Reaching herd immunity is partly dependent on enough people
opting to be vaccinated.
Herd immunity is the point at which enough people are immune to
a disease to make its spread unlikely. Roughly 75% to 80% of the
U.S. population needs to be immune to Covid-19 to reach herd
immunity, some studies estimate. But that number is a moving target
and could rise as new variants emerge. Even if vaccines don't
prevent transmission completely, they can still help populations
achieve herd immunity if enough people take them, says Arnold
Monto, an epidemiology professor at the University of Michigan
School of Public Health who chairs the U.S. Food and Drug
Administration's Vaccines and Related Biological Products Advisory
Committee. "Until we have broad-based vaccination and herd
immunity, we should appreciate that it's possible to still get
exposed to the virus really from anybody whether they're vaccinated
or not," says John R. Mascola, director of the federal National
Institute of Allergy and Infectious Diseases' Vaccine Research
Center. But if the vast majority of people get the vaccine, "some
asymptomatic transmission is not going to have much of a public
health implication," he says.
Read the original article by Sumathi Reddy here.
(END) Dow Jones Newswires
January 18, 2021 12:26 ET (17:26 GMT)
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