Plummeting Cases in U.S. Show Pathway to Crushing Covid-19

Covid-19 cases and hospitalizations are dropping dramatically across the U.S., suggesting that measures to interrupt transmission are working, at least for now.

More than 27.7 million Americans have tested positive among at least 83 million believed to have been infected. A rising number -- 11.8% of the population -- has now received at least one dose of a vaccine. And data gathered from mobile phones suggest people are being more cautious in their day-to-day activities. If cases keep falling, it could buy time for the U.S. vaccination effort to take hold in the warm summer months ahead, potentially underpinning a long-sought economic recovery.

Plummeting Cases in U.S. Show Pathway to Crushing Covid-19

Health experts, meanwhile, are anticipating challenges. Inoculations need to outpace highly contagious variants from the U.K. and South Africa that are now in the U.S. And the upcoming holidays -- Spring Break, Easter and Mother’s Day included -- hold the threat of group gatherings that can swiftly boost the virus’s spread.

“The history of surges is they do come down,” said Robert Wachter, chair of the department of medicine at the University of California-San Francisco. “They generally come down from some combination of changes in behavior, changes in government policy and the impact of immunity.”

Infectious disease experts agree it’s way too early to call an end to the pandemic. The declines follow a surge tied to the Thanksgiving and Christmas holiday season, and infection levels remain roughly on par with trends from last fall at around 91,000 new cases confirmed daily.

Plummeting Cases in U.S. Show Pathway to Crushing Covid-19

Rochelle Walensky, head of the U.S. Centers for Disease Control and Prevention, on Sunday rang a warning bell. “We are nowhere out of the woods,” she said on CBS’s “Face the Nation,” adding that “now is the time to double down” on mitigation efforts.

If those efforts are relaxed “with increasingly transmissible variants out there,” she said, “we could be in a much more difficult spot.”

Walensky’s warning comes as some states, including Iowa and Montana, ease mandates on mask wearing and as the CDC emphasizes that tamping down community spread is key to safely reopening schools -- a priority of the Biden administration.

Early on, the country experienced regional surges in the northeast last spring, Sun Belt states in the summer and Midwest and Western states through the fall. However, the latest surge worsened nearly everywhere in January, producing the deadliest month so far.

Dead Silence

Since then, the numbers have leveled off or declined. Ali Mokdad, a professor of health metrics at the University of Washington’s Institute of Health Metrics and Evaluation, said that after the holiday surge, Americans began to behave much more cautiously.

“If you look at our data, the week after Thanksgiving, the week after Christmas, it was dead silence,” Mokdad said. “People stayed at home, even cell-phone calls went down.”

The country is still far short of herd immunity, the time when the country has so much protection from the dominant strain that it can no longer spread effectively. That will likely require 70% to 85% of the 330 million Americans be either vaccinated or have natural protection, experts say.

At the present vaccination rate, enough doses will have been administered by Spring Break in mid-March to cover about 15% of the U.S. population with two doses, according to the Bloomberg vaccine tracker. By Easter Sunday, that will rise to about 20% and by Mother’s Day enough shots could be given to cover close to 30% of Americans.

These estimates are based on vaccination rates over the last week, and will likely rise substantially as more vaccine supply becomes available. On Tuesday, the vaccination rate in the U.S. was 1.7 million doses per day, on average.

At this rate, it will take an estimated 8 months to cover 75% of the population with a two-dose vaccine.

U.K. Variant

Meanwhile, the highly-contagious U.K. variant, known by scientists as B.1.1.7, is already tied to about 1% to 4% of U.S. infections and is predicted to become the dominant strain by late March or April, according to Gregory Armstrong, director of the Advanced Molecular Detection Program at the CDC.

That may set up a race between vaccine dispersals, which are likely to rise, and the ability of the virus to spread among Americans who aren’t yet immunized, some experts say.

Armstrong emphasized in an interview that the mutation today remains at relatively low levels. Even if the U.K. variant -- which is believed to be 50% more transmissible -- accounted for 10% of all known infections, it would drive cases up by just 5%, according to Armstrong.

That’s “small enough that we’re not even going to be able to detect it,” Armstrong said.

Still, as the variant becomes more prevalent, adherence to measures like mask-wearing, social distancing and vaccination will have to be even better to prevent infections from increasing, he added.

California Mutation

Researchers at Cedars-Sinai recently claimed to have found a U.S. variant in California linked to the holiday season in Los Angeles. That finding has prompted new concern about the role being played to date by the new mutations.

“There’s no consensus yet on what to think of that,” Armstrong said. “Across the U.S., what’s happened in the last several months, this surge that peaked in the beginning of January, a lot of people have looked at this and have not seen anything in the virus itself that would explain it.”

In contrast, B.1.1.7 already made up about 80% of cases in parts of the U.K. by the time early concerns were raised about it, Armstrong said.

The U.S., however, lags behind many other countries, including the U.K., in its genomic surveillance, in which scientists use genetic data to track the spread of different strains of a disease.

Counter Pressure

In the near term, new dominant variants can be expected to exert counter pressure to the forces that are driving cases lower. Meanwhile, holiday seasons and big events that traditionally draw people together have often matched up with case surges.

A stretch of new events and holidays -- from the recent Super Bowl and Chinese New Year to Mardi Gras, St. Patrick’s Day and then Passover and Easter in April -- are expected to test social distancing commitments moving forward.

“Which one wins and whether we have a fourth surge is sort of the great unknown at this point,” said Wachter at the University of California-San Francisco.

Last year’s Mardi Gras festival dramatically accelerated transmission in Louisiana, eventually leading to secondary localized epidemics throughout the South, according to a preprint by scholars at The Scripps Research Institute and Tulane University.

Eventually, Covid-19 may reach an endemic state and become seasonal like other coronaviruses, the common cold and influenza, said Brian Fisher, a senior scholar at the Penn Center for Clinical Epidemiology and Biostatistics. The endemic state will still need to be addressed with vaccines, he said, including updated ones.

“Now, how we get there is up for debate, and there likely will be some increased periods of increased transmission still ahead,” he said.

©2021 Bloomberg L.P.

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