Covid-19: efficacy of vaccines against the delta variant 4:05
(CNN) - The
United States turned its approach to the coronavirus pandemic this week.
Mask wear is back, vaccine mandates looming, and officials seem more concerned than they have in months.
President Joe Biden said Thursday that all federal government employees or contractors will be asked to say if they are vaccinated, and those who are not should wear a mask at work, stay away from others and be tested. of coronavirus at least once a week.
What drives this are two things: the large number of Americans who remain unvaccinated and the rapid spread of the delta variant.
This is what is known so far about the variant.
Delta variant would spread as easily as chickenpox 0:50
What is the delta variant
The delta variant, originally known as B.1.617.2, has been around since late last year, but in recent months it has quickly become dominant in many countries.
It accounts for more than 80% of newly diagnosed cases in the US, according to the Centers for Disease Control and Prevention (CDC).
"Covid-19 cases increased more than 300% nationally from June 19 to July 23, 2021, along with parallel increases in hospitalizations and deaths caused by the highly communicable variant B.1.617.2 (delta)" , the CDC said in a Health Alert Network advisory this week.
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The variant is more transmissible
How much more is not really clear.
Estimates range from 60% higher to over 200%, depending on who is making the estimates.
A CDC document indicates that the delta variant is as transmissible as chickenpox: each infected person infects up to eight or nine, on average.
The original variant of coronavirus, the CDC noted, was as contagious as the common cold, with each infected person infecting two others.
It's a difficult number to verify, because figuring it out would require a lot more testing than is currently being done.
People who test positive would have to submit samples for genomic sequencing, and that's only done in a few places around the country.
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And comparing its transmissibility to past variants would require those kinds of tests to have been done in recent months, and that just wasn't done.
So everything is based on estimates.
British modelers of infectious diseases, a group known as the Scientific Pandemic Influenza Group on Modeling, operational subgroup, say that data indicates that the delta variant is 40-60% more transmissible than the B.1.1.7 or the alpha variant. , which was once dominant in the US but has been replaced by delta.
They say it is almost twice as transmissible as the original variants of the virus that were first seen in China.
Delta could cause more serious illness
Hospital emergency rooms and intensive care units are filling up with patients again in some parts of the U.S. The delta variant may seem to make people sick, but more than 90% of people who present to receive treatment are not vaccinated, according to the CDC and hospital officials who have spoken with CNN.
So while people may be more likely to be infected with delta in the first place if they are not vaccinated, there is no hard data yet to show that delta causes a more serious disease.
People who are vaccinated and infected have the same viral load of the delta variant as unvaccinated people, according to an unpublished study
The CDC cites three older studies from Canada, Singapore and Scotland, which indicate that people infected with delta end up in hospital more often.
What is also happening is that young people represent a higher proportion of those who get sick.
More than 80% of Americans 65 and older are fully vaccinated, according to the CDC.
But younger Americans are not vaccinated at the same rate, so they are the ones who show up in emergency rooms.
It can infect even fully vaccinated people
No vaccine is 100% effective, and yet many thousands of people who are fully vaccinated have become infected, known as a sudden breakthrough.
The CDC released a surprising study Friday looking at an outbreak in Provincetown, Massachusetts, where 74% of the people who became infected were fully vaccinated, and four of them ended up in the hospital.
The outbreak involved 469 people who contracted Covid-19 earlier this month.
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"The tests identified the delta variant in 90% of the 133 patient samples," the CDC researchers and local health departments wrote in the CDC's weekly report.
It is the first large study to contradict previous evidence that vaccinated people are almost completely safe from serious disease, even with delta and other variants.
This was noted in a CDC presentation made to Walensky this week.
"Vaccines prevent more than 90% of serious diseases, but they may be less effective in preventing infection or transmission," he says.
"Therefore (there would be) more (infections) after vaccination and more community spread despite vaccination," he says.
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The CDC now notes this on its website:
"Available evidence suggests that currently licensed mRNA covid-19 vaccines (Pfizer-BioNTech and Moderna) are highly effective against hospitalization and death from a variety of variants including Alpha (B.1.1.7), Beta ( B.1.351), Gamma (P.1) and Delta (B.1.617.2), says the CDC.
"The data suggest less effectiveness against confirmed infection and symptomatic disease caused by the Beta, Gamma, and Delta variants compared to the ancestral variant and the Alpha variant. Continuous monitoring of the effectiveness of the vaccine against the variants is needed." , adds the CDC.
Tests on lab plates had indicated that the immune response generated by the vaccines should, in theory, be strong and broad enough to cover delta.
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More infectious for vaccinated people
than past variants
While the CDC originally told people that those vaccinated are less likely to infect others, the CDC's Walensky said this week that the delta variant may be different.
The Provincetown study released Friday shows that.
"People with covid-19 reported attending densely packed indoor and outdoor events at venues including bars, restaurants, guesthouses, and rental homes," the researchers wrote.
Tests on infected people showed that fully vaccinated people had as much virus in their body as unvaccinated people.
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"Elevated viral loads suggest an increased risk of transmission and raise concerns that, unlike other variants, vaccinated people infected with delta can transmit the virus. This finding is concerning and was a fundamental finding that led to the recommendation of the mask use updated from CDC, "Walensky said in a statement.
Because of this and other tests, the CDC now says that even vaccinated people should wear face masks in areas of moderate or high transmission.
This is because vaccinated people can be exposed and then have enough virus load growing in their bodies to infect another person, even if they have no symptoms.
"The findings of this research suggest that even jurisdictions without substantial or high COVID-19 transmission could consider expanding prevention strategies, including the use of masks in closed public settings regardless of vaccination status, given the potential risk of infection. while attending large public gatherings that include travelers from many areas with different levels of transmission, "wrote the team that reported on the Provincetown outbreak.
Much of what is known comes from a study conducted by researchers in China.
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They found that the viral loads of people infected with delta were 1,000 times higher than those of people infected at the start of the pandemic.
Jing Lu of the Guangdong Provincial Center for Disease Control and Prevention and his colleagues also said the virus spread faster, in four days, compared to six days at the beginning of the pandemic.
People who make statements about delta characteristics often refer to this single study.
For example, New York University infectious disease specialist Dr. Celine Gounder caused a stir when she said that people could become infected with delta in just one second of exposure, compared to 15 minutes at the start of the pandemic.
This was not based on scientific observations.
Gounder was extrapolating from Lu's study, he explained on Twitter.
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Has some unique mutations
The delta variant has a constellation of mutations that characterize it.
Each variant carries a group of different mutations.
When these mutations start to cause a particular lineage of the virus to behave differently or have different effects, it is labeled either a variant of concern or a variant of interest.
Delta has at least three mutations in a structure called the receptor-binding domain - the part of the virus that attaches directly to the human cells it infects.
The structure can help the virus escape detection by the immune system, and at least one helps it bind more closely to cells.
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Another mutation in a place known as the furin cleavage site - it's on the signature spike protein - could also help the virus infect cells more easily, according to the American Society for Microbiology.
"The mutation is believed to increase viral infectivity and transmissibility; however, research indicates that it must occur in the context of additional spike protein mutations to be consistent," says the ASM.
It does not have some of the mutations that made other variants more transmissible, including one called N501Y that characterizes the alpha or B.1.1.7 variant;
the beta variant or B.1.351;
and the gamma or P1 variant.
It also lacks a mutation called E484K that is seen in beta and gamma.
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The answer to the spread, infectious disease experts universally say, is more vaccination.
"If we have more and more people vaccinated, we will win in this race," Walensky said this week.
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Delta variant
