The U.S. has spent months trying to vaccinate those most at-risk of severe illness from COVID-19, from health-care providers and the elderly, to essential workers and those with other underlying medical conditions.

In the weeks ahead, data on COVID hospitalizations and deaths will show whether that strategy is working.

Spikes in case numbers have typically translated weeks later to increasing hospitalizations and fatalities, a dynamic that should abate after the most vulnerable are immunized. While there are early signs that’s happening in places like nursing homes, whether it will hold true with other at-risk groups and younger people remains to be seen. And the moment of truth is arriving just as infections are rising again in many states.

“It’ll be a test of the effectiveness of our vaccination campaigns to reach at-risk populations,” said Josh Michaud, an associate director for global health policy at the Kaiser Family Foundation, an independent nonprofit. All states have at least made those age 65 and older eligible, which means “you’re cutting out something like 80% of the population most at risk of dying.”

The expanding share of Americans who have received COVID-19 vaccines — about 26%, or more than 87 million people, have gotten at least one dose — represents an inflection point in the pandemic’s trajectory and a watershed moment for the U.S., where the virus has sickened at least 30 million and killed more than 547,000.

Yet most people in the U.S. still aren’t protected. And there are major roadblocks in the U.S. race to stay ahead of the virus, including vaccine hesitancy and barriers to access, declines in testing and the emergence of more-contagious variants.


While the number of new cases, hospitalizations and deaths will remain important indicators of the state of the pandemic, there’s a glaring need for more precise ways of measuring COVID-19, public-health experts say.

“Knowing where we have a problem by community and by source is very important to handle the pandemic as we move forward,” said Ali Mokdad, a professor at the Institute for Health Metrics and Evaluation in Seattle, which produces influential COVID-19 projections. “Otherwise, we are flying blind.”

At least for some groups, COVID vaccines are reaching their target audience and doing what they’re supposed to. Among those age 65 and older, an early demographic to qualify for inoculation, about 71% have received at least one dose, according to Centers for Disease Control and Prevention data.

In nursing homes, where inhabitants were also prioritized early for shots, COVID cases among residents have dropped by nearly 98% since mid-December, and deaths by 88%, according CDC data, something industry officials have linked to immunizations.

What that means is that new COVID cases will likely emerge in younger age groups. That occurred in Israel, where infections were recently plateauing despite the country’s world-leading immunization program. It turned out that cases among young people were surging, even as infections dropped in the 50-and-older crowd.

Younger people, though they’re thought to be less likely to have symptoms, can still spread the virus and contract severe cases themselves. In a handful of states, for instance, those with underlying medical conditions don’t yet qualify for shots.


While it’s “extraordinarily good news that our death rate is declining in those who have been vaccinated, there is still a death rate among those who are over 20,” CDC Director Rochelle Walensky said at a White House briefing this week. “As those cases continue to increase in that demographic, we will see death rates in that demographic as well.”

Those risks are top-of-mind in West Virginia, which widened eligibility this week in an effort to interrupt transmission of the virus among young people.

“We think that will buy us more time,” said Clay Marsh, West Virginia’s COVID-19 coordinator and executive dean for health sciences at West Virginia University. “We’d love to hold the variants at bay and try to get a lot of the rest of the population vaccinated.”

In Michigan, where COVID infections are rising again, the ratio of hospitalizations to cases is significantly lower than it was in October, the last time the state saw a surge of this magnitude. About 69% of its 65-and-over cohort — which has typically accounted for half of all COVID hospitalizations and about 4 in 5 deaths — has now had at least one dose of a vaccine.

Still, the Michigan Health & Hospital Association raised alarms this week about hospitalizations spiking among younger age groups: Since early March, they rose 633% among those in their 30s and 800% among those in their 40s. The data show COVID-19 vaccines are working but also “that adults of any age are vulnerable to complications from the disease,” the group said.

While expanding vaccination coverage is the key to the U.S. recovery, it also threatens to further splinter an already-fractured national pandemic response.


Take, for instance, testing levels, which are how U.S. cases get identified and counted. In recent months, those levels have stagnated, and even recently started to decline.

“We’ve completely shifted our focus to vaccines at the expense of testing,” with states even converting testing facilities to administer shots, said Jennifer Nuzzo, a senior scholar at the Johns Hopkins Center for Health Security, adding that “we are potentially losing some insight into where the virus is and where it isn’t, and how quickly it’s spreading.”

And while there are other ways of monitoring COVID trends known as surveillance, such as doing more targeted testing at places like travel hubs, nursing homes or prisons, that never got off the ground in the U.S., Nuzzo said.

That matters because as vaccination coverage expands, virus outbreaks are likely to become more scattered.

“People would be surprised to see the number of people who still remain unvaccinated, particularly among vulnerable groups,” said David Rubin, a physician and director of PolicyLab at Children’s Hospital of Philadelphia, which has been modeling the spread of COVID-19.

CDC epidemiologist Adam MacNeil said in an interview that the agency is setting up surveillance systems to track COVID-19 reinfections and cases in which people who have been immunized get infected, to accompany longtime efforts to track and model infection levels.


Federal and state officials have made virus data at the county level publicly available, but more precise looks at who is affected is often lacking, IHME’s Mokdad and others said. Data for cases and hospitalizations by age group and race or ethnicity, for instance, are infrequently and inconsistently available at the county level, according to PolicyLab’s Rubin.

“We don’t even have that, a year into the pandemic,” he said.

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Bloomberg’s Jonathan Levin and Jill R. Shah contributed to this report.