The coronavirus pandemic continues to sweep across the country; every day, tens of thousands of Americans are reporting new COVID infections, which may be designated as a preexisting condition by insurers. In November, the Supreme Court will consider whether the Affordable Care Act (ACA) requirement to have health insurance is unconstitutional and if it is, whether to strike down all or part of the ACA — and with it, preexisting-condition protections. If the Court ultimately decides to strike down these protections, there could be dire health and financial consequences for people across the age spectrum, including an often-overlooked population, younger adults.

Younger adults are less likely to die from COVID-19, but we are beginning to learn how it affects health over the longer term. It may cause silent damage to the lungs, heart, kidneys, and nervous system — even among those with asymptomatic infections. Other viral infections are known to cause organ damage and cancer. For example, human papilloma viruses can cause cervical cancer in women; hepatitis C virus can cause cirrhosis and liver cancer decades after a silent infection. The novelty of this coronavirus means we do not yet know whether it could cause long-term health effects or how many young adults may be affected later in life.

Uncertainty about long-term health effects may be sufficient for health insurers to designate COVID-19 infection as a preexisting condition. Some may go further and designate anyone who is tested regularly for COVID-19 as having a preexisting condition, even if the test result was negative, because regular testing may indicate a high-risk occupation that increases likelihood of exposure. If young adults forgo testing and survive an infection at home, later health effects would almost certainly be designated as preexisting conditions.

Before the pandemic, an estimated 31 million younger adults ages 18 to 34 had a preexisting condition. Using the methodology of a recent Fund analysis, we estimate that between the beginning of the pandemic and October 26, approximately 3.9 million adults younger than 59 contracted COVID-19 and had no prior reported underlying health condition. Of that group, 2.3 million are ages 20 to 39, including 1.3 million ages 20 to 29. In the next few months, the number of young adults falling into this group may expand more quickly. The pandemic has shifted in the United States, with younger adults now having the highest incidence of infection, according to a recent CDC analysis.

The pandemic-related recession has already put the financial health of young adults at risk. Those younger than 25 accounted for 16 percent of job losses and 7 percent of all job-based health insurance loss between February and June. The continuing rise in unemployment and loss of health coverage may leave young adults with grave financial difficulties. More than a third (37%) of adults ages 19 to 34 reported they suffered from at least one medical bill problem over the past year, including having problems paying medical bills, being contacted by a collection agency for unpaid bills, having to change their way of life to pay their bills, or having medical debt. Of those adults, half had medical debt of $2,000 or more.

Young adults ages 19 to 34 made the largest gains in insurance coverage of any age group since the ACA was passed. Before the ACA, young adults who aged off parents’ plans or Medicaid or the Children’s Health Insurance Program had few affordable options. Now, they can stay on parents’ plans until age 26 or may be eligible for either Medicaid or subsidized marketplace plans.

These paths to coverage for young adults would end if the ACA were overturned. In addition, with the loss of preexisting-condition protections, young adults could face dire challenges accessing and affording health care for years to come, as well as unknown long-term health complications from COVID-19 infection.