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Monday, September 27, 2021

Vaccinated people may spread the virus, though rarely, CDC reports

The evolving research into the delta variant has humbled scientists worldwide, who now confront fresh questions about the virus they had not considered.

By: New York Times | Washington |
Updated: August 1, 2021 12:08:44 pm
A health care worker administers a COVID-19 test at a drive-thru testing site in Oakland. (The New York Times/File)

Written by: Apoorva Mandavilli

In yet another unexpected and unwelcome twist in the pandemic, the Centers for Disease Control and Prevention (CDC) released a report on Friday strongly suggesting that fully immunised people with so-called breakthrough infections of the delta variant can spread the virus to others just as readily as unvaccinated people.

The vaccines remain powerfully effective against severe illness and death, and the agency said infections in vaccinated people were comparatively rare. But the revelation follows a series of other recent findings about the delta variant that have upended scientists’ understanding of the coronavirus.

In the new report, which was intended to explain the agency’s sudden revision to its masking advice for vaccinated Americans, the CDC described an outbreak in Provincetown, Massachusetts, this month that quickly mushroomed to 470 cases in Massachusetts alone, as of Thursday.

Three-quarters of the infected were fully immunized, and the delta variant was found in most of the samples that were genetically analyzed. Vaccinated and unvaccinated people who were infected carried high levels of the virus, the agency reported.

“High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with delta can transmit the virus,” Dr Rochelle Walensky, director of the CDC, said Friday.

The viral load data indicate that even fully immunised people can spread the virus as easily as unvaccinated people who become infected. “We believe at individual level they might, which is why we updated our recommendation,” Walensky said in an email to The New York Times earlier this week.

Dr Rochelle Walensky, director of the US Centers for Disease Control and Prevention (CDC). (The New York Times/File)

An internal agency document, which was obtained Thursday night by the Times, suggested even greater alarm among CDC scientists and raised harrowing questions about the virus and its trajectory.

The delta variant is about as contagious as chickenpox, the document noted, and universal masking may become necessary. Still, breakthrough infections overall are infrequent, according to the agency.

On Friday, the Kaiser Family Foundation reported that the rate of breakthrough cases is less than 1% among fully vaccinated people in states that keep such data.

The gathering research into the variant throws into disarray the country’s plans to return to offices and schools this fall, and revives difficult questions about masking, testing and other precautions that Americans had hoped were behind them.

Government officials and scientists alike are gravely concerned that the findings may shake faith in the vaccines, hobbling the nation’s lagging immunization campaign, should Americans infer incorrectly that the shots are not effective.

Concerned by the lagging campaign, President Joe Biden has ordered that all federal employees be vaccinated or face weekly virus testing. Support for vaccination mandates is growing among some corporations and in some parts of the country.

The evolving research into the delta variant has humbled scientists worldwide, who now confront fresh questions about the virus they had not considered.

They do not fully understand the circumstances that may increase the odds of a breakthrough infection, for example, nor who may be most at risk. They do not know for certain that the delta variant causes more severe disease in the unvaccinated who become infected, although early data suggest it does.

“We spent so much time and energy and treasure trying to figure out this damn virus last year, and how it works and all the things it does,” said Dr Robert Wachter, chairman of the Department of Medicine at the University of California, San Francisco.

Learning just how different the delta variant is from the original virus is “just jarring,” he added. “The brain doesn’t like to keep being jerked around like this.”

Even if breakthrough infections are rare, the new data suggest the vaccinated may be contributing to increases in new infections — although probably to a far lesser degree than the unvaccinated. Breakthrough infections were always anticipated, but until the delta variant arrived, vaccinated Americans were not believed to be drivers of community spread.

Nationwide, about 97 per cent of people hospitalized with COVID-19 are unvaccinated, according to data from the CDC. And the unvaccinated are far more likely to spread the virus to others in their communities.

“Full vaccination is very protective, including against delta,” said Angela Rasmussen, a research scientist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada.

“Masks are a wise precaution, but the bulk of transmission is among the unvaccinated and that’s still who is most at risk,” she added.

The gathering research underscores the urgency to pick up the pace of vaccination in the United States and decrease the number of people susceptible to severe illness. This week, the rate of vaccination in the European Union exceeded that in the United States for the first time.

About 58 per cent of Americans ages 12 and older are fully vaccinated. The pace of vaccination has slowed to just over 500,000 people per day, although it has begun curving slightly upward in the past couple of weeks as infections rise again.

In its report Friday, the CDC urged local and state officials in jurisdictions with even lower levels of the virus to consider putting into effect precautions, such as masking and limiting gatherings. The CDC’s internal document sounded more urgent, recommending that the agency “acknowledge the war has changed.”

An employee and a customer both wear masks at a salon in Los Angeles. (Alex Welsh/The New York Times)

Indeed, the questions now facing Americans seem nearly inexhaustible, almost insoluble. Should companies have employees return to workplaces if vaccinated people might, on occasion, spread the variant? What does this mean for shops, restaurants and schools? Are unmasked family gatherings again off the table?

With the number of daily cases up to nearly 72,000 on average as of Friday, the new data suggest that immunized people with young children, ageing parents, or friends and family with weak immune systems may need to wear masks to protect vulnerable people in their orbit — even in communities with lower infection rates.

Scientists warned even last year that the vaccines might not completely prevent infection or transmission. But experts did not expect that these infections would figure significantly in the fight against the virus, nor did they anticipate how quickly the delta variant would tear through the country.

“I thought two months ago that we were over the hump,” Wachter said. In San Francisco, the most highly vaccinated big city in the country, 77 per cent of people over age 12 are vaccinated.

And yet, the hospital where he works has seen a sharp rise, from one case of COVID-19 on June 1 to 40 now. 15 of the patients are in intensive care.

“If getting to 70 or 75 per cent immunity doesn’t protect the community, I think it’s very hard to extrapolate what happens to a place that is 30 per cent vaccinated,” Wachter said. “Humility may be the most important thing here.”

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