Even after
just one dose of the mRNA vaccines made by Pfizer and Moderna, the vaccines
reduced the
chance of getting infected with SARS-CoV-2, researchers report March
29 in Morbidity and Mortality Weekly Report. “We clearly showed in
our study that if you were at least 14 days out from your first shot, you had
80 percent protection” from infection, says Jeff Burgess, associate dean for
research at the Mel and Enid Zuckerman College of Public Health at the
University of Arizona in Tucson. The study is part of a growing body of
evidence suggesting that the vaccines not only reduce the risk of getting
seriously ill with COVID-19, but can prevent catching the virus in the first
place.
“If you
can’t get infected, you can’t infect anyone else, which means the vaccines can
reduce transmission as well as the disease,” says Marm Kilpatrick, an
infectious diseases researcher at the University of California, Santa Cruz, who
was not involved in the study.
That is
welcome news coming on the heels of data indicating that cases,
hospitalizations and deaths are on the rise again in the United States as
states lift mask mandates and open businesses at full capacity.
“Right now
I’m scared,” Rochelle Walensky, director of the U.S. Centers for Disease
Control and Prevention said during a White House
briefing on March 29, noting “the recurring feeling I have of
impending doom.” She urged people to “hang on a little longer” and continue to
wear masks, social distance and get vaccinated to head off a potential fourth
surge of the disease. “We have so much to look forward to. So much promise and
potential of where we are and so much reason for hope,” she said.
Part of the
reason for hope comes from the MMWR study. The study “is
tremendously encouraging and complements other recent studies,” Walensky said.
Nearly 4,000
health care workers, first responders and other essential workers in six states
took part in the study led by CDC researchers. From December 14 through March
13, the workers submitted weekly nasal swabs for coronavirus testing. Both
symptomatic and asymptomatic infection rates fell after vaccination. A small
number of vaccinated people in the study still got infected.
Other
real-world data collected from health care workers in California and Texas also
seem to back up those findings, researchers say in separate reports published
March 23 in the New England Journal of Medicine. In the Texas
report, 234 of 8,969 nonvaccinated employees at the University of Texas
Southwestern Medical Center in Dallas tested positive for the coronavirus from
December 15 to January 28. That’s 2.61 percent, compared with 1.82 percent (112
of 6,144) of employees that had gotten one shot and 0.05 percent (four of
8,121) of fully vaccinated employees.
In the
California report, infections among health care workers also fell with
increasing vaccination levels. Only seven infections occurred among 4,167
people who were at least 15 days out from getting their second dose of vaccine.
The vaccines prevented health care workers in the study from becoming seriously
ill, says study coauthor Francesca Torriani, an infectious diseases physician
and hospital epidemiologist at the University of California, San Diego.
Reducing the
severity of illnesses will help relieve the burden on hospital systems if there
should be a fourth wave, she says. But to really stop transmission of the
virus, it’s important to vaccinate 18- to 30-year-olds. “Those are the ones who
are right now transmitting the disease.” Motivating healthy young people who
are less likely to become severely ill in the first place to take the shots
could be difficult, Torriani says. “There’s not much in it for them, but there
is a lot in it for their families, so I’m hoping that realization” will push
young people toward getting vaccinated.
Because some
vaccinated people can still get infected, the CDC and other public health
agencies have recommended that people who have gotten their shots continue to
wear masks in public and take other precautions to avoid spreading the virus.
Data from
Israel does suggest that the Pfizer vaccine might block
transmission of the virus (SN: 2/12/21). Unvaccinated people
produce 2.58 to 4.5 times more virus than
vaccinated people do, researchers report March 29 in Nature Medicine.
Those data show vaccinated people have a lower “viral load” and are less likely
to pass the coronavirus to others if they do become infected, but the effect is
not as strong as might be hoped to truly limit transmission, Kilpatrick says.
That reduction in viral load amounts to about an 11 percent decrease in
infectiousness, he says. “That’s good … but you’d like to be half as infectious
or three-quarters lower infectiousness.”
There is not
yet enough data to say for sure that vaccines prevent transmission, Torriani
says. “There is definitely heavy suggestion,” but further studies on viral load
are needed.
So are data
from everyday citizens. Aside from the MMWR study, almost all
of the real-world vaccine data collected so far in the United States has been
among health care workers. Those workers may not give a true picture of
transmission risks because they have better personal protective equipment and
ventilation than the average person does, Torriani says. Far more indicative
would be studies to determine whether vaccinated people are less likely to
infect household members. “If [household transmission] goes away with
vaccination, that would be the proof.”
Source:
https://www.sciencenews.org/article/coronavirus-covid-vaccine-moderna-pfizer-transmission-disease
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