Briefing

What does the Delta variant mean for the fully vaccinated?

The U.S. is seeing a surge in COVID-19 cases driven by the Delta variant. Just how dangerous is it? Here's everything you need to know.

The U.S. is seeing a surge in COVID-19 cases driven by the Delta variant. Just how dangerous is it? Here's everything you need to know.

What is the Delta variant?

The Delta variant of SARS-CoV-2 — the coronavirus that causes COVID-19 — was first identified in India in December 2020. After ravaging India and sweeping through Great Britain, the Delta variant is now the dominant strain in the U.S., accounting for more than 83 percent of COVID-19 infections

Is Delta more dangerous?

The World Health Organization calls Delta "the fastest and fittest" of the variants, and they don't mean it as a compliment. The Delta mutation modified the protein spikes the coronavirus uses to attach to and infect cells, and those mutations make it at least twice as transmissible as the original strain. Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, called the Delta variant "one of the most infectious respiratory viruses we know of and that I have seen in my 20-year career." The Delta strain doesn't appear to be intrinsically more fatal, but people infected with the variant have a viral load 1,000 times greater than those infected with earlier mutations, according to preliminary research, and they shed more virus for a longer period of time. The massive quantity of virus means more chances to infect a person's cells, and the more the Delta variant spreads in a community, the higher the odds an individual will come in contact with infected people and get blasted with an amount of coronavirus that will make them sick. 

Do the vaccines still work?

Thankfully, yes. All three vaccines approved for emergency use in the U.S. — Pfizer/BioNTech, Moderna, and Johnson & Johnson — and others not yet approved — have proved extremely effective against the Delta variant. The vaccines appear to be about 90 percent effective at preventing serious illness and hospitalization, and 99.5 percent of U.S. COVID-19 deaths this year have been among unvaccinated people. But the vaccine isn't 100 percent effective and it isn't an impenetrable shield against COVID-19, especially when the virus is spreading freely.

Should vaccinated people worry about "breakthrough" infections?

The CDC no longer tracks mild or moderate "breakthrough" infections — instances in which vaccinated individuals contract the virus — so we don't know exactly how common they are. But the CDC does track severe infections among fully vaccinated Americans, and as of July 12, there were 5,492 cases reported, including 1,063 deaths. That is a miniscule fraction of the 159 million vaccinated Americans, but breakthrough infections do happen — and are expected to happen. At the same time, "they tend to be mild — they tend to be more like a cold," says Dr. Carlos del Rio, infectious disease epidemiologist at Emory University. 

These charts illustrate the difference in fatality rates between waves of COVID-19 infections before and after a country is significantly vaccinated. 

Honestly, "I think we are misusing the term breakthrough," says Dr. Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia. "If someone who is fully vaccinated is subsequently hospitalized or killed by the virus, that's a breakthrough case," but in the overwhelming majority of cases, "the vaccine is still doing what it is designed to do — keep people out of the hospital and out of the morgue."

Should vaccinated people wear masks?

The concensus among most public health experts is that wearing a mask can't hurt, especially in situations where the risk of transmission is higher, like crowded enclosed spaces, or if you're immune compromised. "Avoiding crowded spaces and wearing a mask when you're indoors and don't know the vaccination status of those around you is a good idea," writes Tara Parker-Pope at The New York Times. On the flip side, the CDC, citing limited evidence, says vaccinated people are less likely to infect others than unvaccinated people with asymptomatic cases. That would make sense, because people who got vaccinated generally have a lower viral load, which "makes it less likely for you to transmit — not impossible by any means but less likely," says Dr. Monica Gandhi at University of California, San Francisco.

How about booster shots?

The Food and Drug Administration has not authorized a booster shot of a COVID-19 vaccine, and health experts say it won't be necessary to counter the Delta variant or any other probable mutations in the near future. But on Friday, the Biden administration announced it had purchased an additional 200 million Pfizer doses just in case the data proves otherwise and boosters become necessary in the fall or spring. A CDC advisory panel has expressed preliminary support for giving booster shots to some immunocompromised Americans. If a future variant thwarts the current vaccines, a new booster vaccination may be needed.

Is that likely to happen?

It's hard to say, but experts are worried. The Delta variant is also suring in Asia, the Middle East, Africa, Latin America, and Europe, and "the more uncontrolled spread, the more risk of even more dangerous variants," says Dr. Tom Frieden, former CDC director. "Variants remain the wild card for the trajectory of the pandemic. Delta may not be the worst strain the virus deals us." Public health experts will be watching hospitalization data carefully in coming months for signs of a surge in vaccinated people becoming seriously ill, which might indicate a change in the virus. "Right now, it's Delta," says MIT medical director Dr. Cecilia Stuopis. "In the fall it may be Kappa or some other, fitter, variant. We can't be complacent. We are going to be living with this virus in some form or another for the foreseeable future, but our actions right now can determine what that future will be."

Recommended

A plant-filled home could help prevent infections, study finds
Person watering house plants
plant prevention

A plant-filled home could help prevent infections, study finds

Millions of Americans poised to lose Medicaid coverage on April 1
Doctor holding clipboard.
healthcare at risk

Millions of Americans poised to lose Medicaid coverage on April 1

Honeybees help gather data about a city's health
Honeybee on flower.
buzz buzz

Honeybees help gather data about a city's health

FDA approves overdose drug Narcan as 1st over-the-counter opioid treatment
Narcan in a vending machine.
Lifesavers

FDA approves overdose drug Narcan as 1st over-the-counter opioid treatment

More on Delta variant

Should you get a COVID booster shot as soon as you are eligible?
COVID booster shots
Yes

Should you get a COVID booster shot as soon as you are eligible?

California and New Mexico join Colorado, open COVID boosters to all adults
Woman getting booster shot
Vaccination Nation

California and New Mexico join Colorado, open COVID boosters to all adults

Economy slows to 2 percent annual growth
Hiring sign
'a lot of damage'

Economy slows to 2 percent annual growth

Officials keeping 'close watch' on Delta subvariant
London, England.
keeping watch

Officials keeping 'close watch' on Delta subvariant

Former FDA commissioner suggests every household have a supply of at-home COVID-19 tests
Scott Gottlieb.
sunday shows

Former FDA commissioner suggests every household have a supply of at-home COVID-19 tests

Scientists say 'premature' to predict if there will be another major COVID-19 wave, but room for optimism
COVID-19 testing site.
the coronavirus crisis

Scientists say 'premature' to predict if there will be another major COVID-19 wave, but room for optimism

Outside experts are reportedly advising the White House to scrap its universal COVID-19 booster plan
Joe Biden.
solving covid

Outside experts are reportedly advising the White House to scrap its universal COVID-19 booster plan

FDA approval of Pfizer vaccine had 'modest' effect on hesitancy
Pop-up vaccine clinic sign.
the great vaccine debate

FDA approval of Pfizer vaccine had 'modest' effect on hesitancy

'Too soon' to tell if Americans can gather safely for holidays, Fauci says
Anthony Fauci.
sunday shows

'Too soon' to tell if Americans can gather safely for holidays, Fauci says

Incentives key to United Airlines' 'extremely effective' vaccine mandate
United plane.
vaccine mandates

Incentives key to United Airlines' 'extremely effective' vaccine mandate

Pfizer CEO: 99 percent chance Delta-specific vaccine won't be necessary
Albert Bourla.
solving covid

Pfizer CEO: 99 percent chance Delta-specific vaccine won't be necessary

Public still 'hugely underestimating' how much more dangerous COVID-19 is for the elderly
COVID-19 testing site.
the coronavirus crisis

Public still 'hugely underestimating' how much more dangerous COVID-19 is for the elderly

The not-so-terrible challenge for future trials of COVID-19 therapeutics
Pfizer vaccine.
solving covid

The not-so-terrible challenge for future trials of COVID-19 therapeutics

It's the virus, stupid
President Biden.
Picture of Noah MillmanNoah Millman

It's the virus, stupid

Pfizer CEO expects to submit children's COVID-19 vaccine data to FDA in days
Albert Bourla.
sunday shows

Pfizer CEO expects to submit children's COVID-19 vaccine data to FDA in days

COVID-19 booster discussions have sparked a 'communications crisis'
Pfizer-BioNTech vaccine.
the booster question

COVID-19 booster discussions have sparked a 'communications crisis'

Stuck in the pandemic
A COVID hole.
Picture of Damon LinkerDamon Linker

Stuck in the pandemic

Fauci not disappointed by FDA advisory panel's COVID-19 booster recommendation
Anthony Fauci.
sunday shows

Fauci not disappointed by FDA advisory panel's COVID-19 booster recommendation

CNN's Jake Tapper presses Mississippi governor on COVID-19 policies in contentious interview
Jake Tapper, Tate Reeves.
sunday shows

CNN's Jake Tapper presses Mississippi governor on COVID-19 policies in contentious interview

Why doctors don't think vaccine skeptics' acceptance of a helpful COVID-19 treatment is sufficient
Monoclonal antibody treatment.
the coronavirus crisis

Why doctors don't think vaccine skeptics' acceptance of a helpful COVID-19 treatment is sufficient

Idaho doctors and nurses 'beyond frustrated' by COVID misinformation
Nurses.
the fourth wave

Idaho doctors and nurses 'beyond frustrated' by COVID misinformation

The insanity of leaving Africa unvaccinated
A protestor.
Picture of Ryan CooperRyan Cooper

The insanity of leaving Africa unvaccinated

How the dearth of ICU beds threatens non-COVID patients
Doctor in hospital.
'this is an everyone issue'

How the dearth of ICU beds threatens non-COVID patients

Biden's booster headache
President Biden.
Picture of Joel MathisJoel Mathis

Biden's booster headache