The US Centers for Disease Control and Prevention said Friday that a new batch of data from a large study of health care workers across the country helped prompt the agency to say fully vaccinated people can go without masks in most circumstances.
According to the study, real-world use of the Moderna and Pfizer vaccines provided 94 per cent protection for front-line workers immunized at the start of the vaccine rollout. The CDC-led team reported in the agency’s weekly report, the MMWR, that a single dose provided 82 per cent protection.
The findings of the new study, combined with previous research, prompted the CDC to loosen its recommendations on who should wear masks and when according to CDC Director Dr Rochelle.
According to CDC Director Dr Rochelle Walensky, the findings of the new study, combined with previous research, prompted the CDC to loosen its recommendations on who should wear masks and when.
“This report provided the most compelling information to date that COVID-19 vaccines were performing as expected in the real world,” Walensky said in a statement Friday.
“COVID-19 vaccines are effective at preventing COVID-19 disease, especially severe illness and death,” CDC says on its new web page describing guidance for the fully vaccinated.
“COVID-19 vaccines reduce the risk of people spreading COVID-19.”
After weeks of warning people that even fully vaccinated people could have the virus in their noses, mouths, or throats and breathe or spit it out onto others, the CDC now says that evidence shows this is unlikely.
The reason for this is viral load. At least three major studies have found that people who have been fully vaccinated are unlikely to test positive for coronavirus, indicating that they do not carry it in their bodies whether they have symptoms or not.
On March 29, a group of researchers released a study through the CDC that included nearly 4,000 health care workers who tested themselves weekly. That is the only true way to tell if people become infected with the virus but do not develop symptoms.
Approximately 63% of them had been immunized.
The research team discovered that only about 11% of the people had asymptomatic infections at the time. Those who received both doses of either Pfizer/or BioNtech’s Moderna’s vaccine were 90 per cent less likely to have a positive test, while those who received only one dose received 80 per cent protection.
A similar study from Israel, published on the same day in the journal Nature Medicine, discovered that vaccinated people who became infected had a fourfold lower viral load than unvaccinated people.
“In this analysis of a real-world dataset of positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) test results after inoculation with the BNT162b2 messenger RNA vaccine (Pfizer’s), we found that the viral load was substantially reduced for infections occurring 12–37 days after the first dose of vaccine,” Roy Kishony of the Technion – Israel Institute of Technology and colleagues wrote.
“These reduced viral loads hint at a potentially lower infectiousness, further contributing to vaccine effect on virus spread.”
The latest study was released Friday.
“This assessment, conducted in a different study network with a larger sample size from across a broader geographic area than in the clinical trials, independently confirms U.S. vaccine effectiveness findings among health care workers that were first reported March 29,” the CDC said in a statement.
“This study, added to the many studies that preceded it, was pivotal to CDC changing its recommendations for those who are fully vaccinated against COVID-19.”
More than 1,800 workers participated in the study, which compared those who tested positive for coronavirus to those who tested negative.
“Health care personnel are at high risk for COVID-19,” the report reads. “The early distribution of two mRNA COVID-19 vaccines (Pfizer-BioNTech and Moderna) to health care personnel provided an opportunity to examine vaccine effectiveness in a real-world setting,” they added.
“The first U.S. multisite test-negative design vaccine effectiveness study among health care personnel found a single dose of Pfizer-BioNTech or Moderna COVID-19 vaccines to be 82% effective against symptomatic COVID-19 and 2 doses to be 94% effective.”
The risk of infection is decreasing as more Americans are vaccinated, according to 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 per cent of the US population has received at least one dose of the Covid-19 vaccine, with approximately 36 per cent fully vaccinated.
“The transmission rates are going way down,” Hotez told reporters on Friday.
“And I think the other piece that’s important is the data coming out of real-life situations like Israel, showing that anyone who does get breakthrough asymptomatic infection — which is very uncommon — has dramatically reduced virus loads and virus shedding, so this is interrupting transmission, which is just such good news and so exciting.”
In theory, if only fully vaccinated people did not wear masks, there should be little chance of the virus spreading. However, most states in the United States have dropped mask mandates, and more are following the CDC’s advice.
Some critics have expressed concern that the CDC has made no provision for people who have not been immunized but refuse to wear masks.
And, according to President Joe Biden, Americans will be on the honour system when it comes to ensuring they are vaccinated before discarding face masks. “We’re not going to go out there and arrest people,” Biden said Thursday.
There are some caveats to the new guidance’s science. At the moment, it appears that the approved vaccines are very effective against new variants of the virus that are emerging—but this is not certain.