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What is the science behind the CDC decision on masks?

2021-05-21T09:37:10.283Z


After weeks of telling people that even vaccinated people can carry the virus in their nose, mouth or throat and breathe it in or spit it out, the CDC now says the evidence shows this is unlikely.


CDC: Vaccinated should no longer wear masks in the US 1:44

(CNN) -

A new batch of data from a large study of healthcare workers across the country helped prompt the U.S. Centers for Disease Control and Prevention (CDC) to say that people completely vaccinated may not wear masks in most circumstances, the agency said Friday.

The study found that real-life use of the Moderna and Pfizer vaccines provided 94% protection for immunized front-line workers at the beginning of the vaccine launch.

A single dose provided 82% protection, the CDC-led team reported in the agency's weekly report, the MMWR.

It was the new study's findings, in addition to previous studies, that prompted the CDC to decide to relax its advice on who needs to wear masks and when, said CDC Director Dr. Rochelle Walensky.

"This report provided the most compelling information to date that COVID-19 vaccines were working as expected in the real world," Walensky said in a statement Friday.

"Covid-19 vaccines are effective in preventing covid-19 disease, especially serious illness and death," says the CDC on its new website that outlines a guide for those who are fully vaccinated.

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"Covid-19 vaccines reduce the risk of people transmitting covid-19."

After weeks of telling people that even fully vaccinated people can carry the virus in their nose, mouth, or throat and breathe it in or spit it out at other people, the CDC now says the evidence shows this is unlikely.

The reason: viral load.

At least three major studies have shown that fully vaccinated people are unlikely to test positive for the coronavirus, indicating that they do not carry it in their bodies, whether or not they have symptoms.

On March 29, a network of researchers published a study through the CDC that involved nearly 4,000 healthcare workers who underwent weekly tests.

That is the only real way to know if people are infected with the virus without developing symptoms.

About 63% of them were vaccinated.

Only about 11% had asymptomatic infections, the research team found at the time.

Those who received both doses of the Pfizer / BioNtech or Moderna vaccine were 90% less likely to test positive, and those who received only one dose were 80% protected.

A similar study from Israel, published the same day in the journal Nature Medicine, found that vaccinated people who became infected had a lower viral load, four times lower than unvaccinated people.

“In this analysis of a real-world data set of positive test results for severe acute acute respiratory syndrome coronavirus 2 (SARS-CoV-2) after inoculation with the BNT162b2 messenger RNA vaccine (Pfizer), we found that viral load was substantially reduced for infections occurring between 12 and 37 days after the first dose of vaccine, "wrote Roy Kishony of the Technion Israel Institute of Technology and colleagues.

"These reduced viral loads point to potentially lower infectivity, further contributing to the effect of the vaccine on the spread of the virus."

The latest study was published on Friday.

“This evaluation, conducted in a different study network with a larger sample size over a wider geographic area than in clinical trials, independently confirms the US vaccine effectiveness findings among US workers. health that were first reported on March 29, "the CDC said in a statement.

"This study, in addition to the many studies that preceded it, was instrumental in the CDC changing its recommendations for those who are fully vaccinated against COVID-19."

The study involved more than 1,800 workers and compared people who tested positive for coronavirus with those who tested negative.

"Healthcare personnel are at high risk of contracting COVID-19," the report reads.

"The early distribution of two covid-19 mRNA vaccines (Pfizer-BioNTech and Moderna) to healthcare personnel provided an opportunity to examine the effectiveness of the vaccine in a real-world setting," they added.

Israel, no face masks in the open 0:37

Real data show little risk of breakthrough infection

"The first multi-site negative test design vaccine effectiveness study in the US among healthcare personnel found that a single dose of Pfizer-BioNTech or Moderna Covid-19 vaccines is 82% of effectiveness against the symptomatic covid-19 and 2 doses to have an effectiveness of 94% ».

With more Americans vaccinated, the risk of infection is decreasing, said Dr. Peter Hotez, a vaccine expert and dean of the school of tropical medicine at Baylor College of Medicine in Houston.

According to CDC data, nearly 47% of the US population has received at least one dose of the COVID-19 vaccine and approximately 36% of the US population is fully vaccinated.

"Transmission rates are going down," Hotez told CNN's Alisyn Camerota and Victor Blackwell on Friday.

“And I think the other piece that is really important is the data that comes from real-life situations like Israel, which shows that anyone who gets an advanced asymptomatic infection, which is very rare, has drastically reduced the virus load. and moving, so this is really disrupting the broadcast, which is very good news and very exciting.

In theory, if only fully vaccinated people were to remove their mask, there should be little risk of spreading the virus.

But most US states have removed the mask mandates and more are removing them after the CDC's guidance.

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They warn of risks for eliminating the use of face masks in Texas 2:16

Confusing guidelines

Some critics have complained that the CDC did not take action for people who have not been vaccinated but will not wear masks.

“While we all share the desire to return to normal without masks, today's CDC guidance is confusing and does not take into account how it will affect essential workers who face frequent exposure to people who are not vaccinated and refuse to wear face masks, ”Food and Commercial Workers Union President Marc Perrone said Thursday.

And President Joe Biden confirmed that Americans will rely on the good faith system to ensure they are vaccinated before disposing of face masks.

"We are not going out to arrest people," Biden said in remarks Thursday.

There are some caveats to the science behind the new guide.

Right now, it appears that licensed vaccines are very effective against emerging new variants of the virus, but that's not certain.

"Early data shows that vaccines may work against some variants but may be less effective against others," notes the CDC.

Other unknowns include how well vaccines protect people with weakened immune systems, including cancer patients and people with autoimmune disorders who take immunosuppressive drugs.

Also, the CDC says, it's unclear how long the coronavirus vaccine's protection lasts, although studies indicate it's at least six months and probably longer.

Walensky denies that the changes were made to motivate people to get vaccinated, although many public health experts had urged the CDC to make the changes as an incentive.

In April, when the CDC said fully vaccinated people should wear masks indoors when around other people, the agency noted that encouraging people to get vaccinated could be a legitimate factor in changing the guidance.

"In summary, relaxing certain preventive measures for fully vaccinated people can be a powerful motivator for vaccination and should therefore be an important goal of the US vaccination program," say those guidelines, which are still in use. found on the CDC site.

Covid-19 vaccine against covid-19

Source: cnnespanol

All news articles on 2021-05-21

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