The light at the end of the pandemic tunnel is getting brighter. This week, the first health care workers will receive the first doses of an FDA-approved coronavirus vaccine. Soon, so will other front-line workers in health care and beyond, and residents of long-term care facilities.

The availability of COVID-19 vaccines, however, will not necessarily result in people getting fully vaccinated.

For the first vaccines that will reach the public, everyone who gets a first dose must have a second dose within a few weeks to get full protection against severe COVID-19.

While Mark Fendrick, M.D. hails the rapid development of vaccines as a scientific breakthrough, he is anxious.

For decades, the University of Michigan primary care physician and researcher has studied what it takes to make sure that Americans get the essential preventive services that can help them stay healthy.

So what's his worry?

"There are several factors and behaviors that prevent many well-intentioned people from completing a two-step process, like that recommended for the COVID-19 vaccines," he says. "We need to provide everything necessary to support those who receive the first shot to make sure they complete their second dose."

This lack of completion has been well established for other two-dose vaccines, like those that prevent less contagious and less lethal conditions, such as shingles, human papilloma virus (HPV), and hepatitis B. Fendrick worked on studies of the latter vaccine early in his career.

"On the positive side, out-of-pocket costs - one of the most significant barriers for vaccine uptake -- has been removed for COVID-19 vaccines, thanks to federal action," says Fendrick, a general internist at Michigan Medicine and director of the Center for Value-Based Insurance Design, which has fostered research and policy initiatives to enhance access to preventive care.