A leading US disease expert says there's 'no doubt in my mind' vaccinated people are helping spread Delta

singer on stage in crowded room — Gretchen Gustafson of White Ford Bronco interacts with the crowd during a show at Union Stage on June 11, 2021 in Washington, DC. DC recently lifted capacity restrictions for bars, nightclubs, and venues.
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Vaccinated people are well protected from severe illness and death, even with the Delta variant surging.
But it is possible for fully vaccinated people to catch asymptomatic case of COVID-19 and spread it to others.
A top disease modeler, who advises the White House, said vaccinated people should still wear masks.
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The US is celebrating robust COVID-19 vaccine coverage.

Strangers are standing shoulder to shoulder in bars, fans are singing at packed indoor concerts, and travelers are flying in numbers not seen since before lockdowns began in 2020.

"While the virus hasn't been vanquished, we know this: It no longer controls our lives," President Biden said on July 4th, as hospitalizations, cases, and deaths trended down. "America is coming back together."

Yet, a quiet new wave of severe COVID-19 infections is brewing, fueled by the more transmissible Delta variant.

"We actually have states where hospitalizations are going up more than cases," Christopher Murray, director of the Institute for Health Metrics and Evaluation, told Insider, stressing CDC data may mask the virus's true spread.

"CDC guidance is not to test the vaccinated [unless they're symptomatic], so we're probably missing a bunch of transmission in vaccinated individuals."

Delta is spreading quickly in the US

a crowded line of travelers with rollerbags waiting at john wayne airport in california — Travelers wait at John Wayne Airport in Santa Ana, California on June 30, 2021.
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Drilling into state-level data reveals how quickly Delta has spread.

"We have 14 states where transmission has started to go back up," said Murray, who is the lead modeler at the IHME, which the White House has leaned on for disease projections throughout the pandemic.

That's "due to the Delta variant, and the fact that everybody's stopped wearing a mask and just basically stopped most precautions," he added.

Disease modelers at Scripps estimate that Delta could now be responsible for around 60% of COVID-19 cases across the US.

Vaccines prevent serious illness

COVID-19 vaccines don't prevent every infection. They are designed to better defend your body against the virus. The US-authorized vaccines do that very well - even against Delta.

Some vaccinated people get a mild, cold-like illness, with a headache and a runny nose. Others could get infected but never know it, becoming silent spreaders.

Delta wreaks far greater havoc among the unvaccinated. Hospitalizations are trending up in several US states, including Missouri, Arkansas, Utah, and Mississippi, according to IHME's data. Those are some of the same places where vaccine rates lag.

a map of the US showing the number of adults vaccinated with at least one dose of a COVID-19 vaccine, county by county, with areas of low coverage highlighted in the southeast and Midwest — The share of American adults who've had at least one dose of any COVID-19 vaccine varies dramatically by region and county.
CDC

How Delta can move through a semi-vaccinated population

Tim Spector, an epidemiologist at King's College London, previously told Insider that, while there's no evidence Delta is more deadly, it is more infectious, and "because of that extra stickiness, it's going to still keep breaking through the vaccine group."

More than half of Scotland is fully vaccinated, and 71% of Scots have received at least one dose of a vaccine. Yet the country is suffering its worst wave of infections yet.

"You cannot explain the explosive epidemic in Scotland, in a pretty highly vaccinated population, if they're not playing a role in transmission," Murray said of the vaccinated.

Delta versus our vaccines

A recent real-world study from the UK suggests Pfizer's vaccine is about 88% effective against symptomatic COVID-19 with Delta - markedly lower than the 95% efficacy against the first-detected COVID-19.

Moderna and Johnson & Johnson, too, may be less effective at preventing symptomatic infections with Delta, according to early lab studies by those companies.

What's clear is that all three US-authorized vaccines maintain strong protection against severe disease and death, even with the Delta variant.

While natural immunity may help (and federal estimates suggest more than one third of Americans have had COVID-19), Russia is an example of how prior infections can't halt Delta's spread.