Many states are rolling back restrictions and masking guidance now that just over half of American adults are vaccinated against COVID-19. But public health experts say this summer could be a crucial moment for contact tracing -- the process of identifying those exposed to communicable infectious disease.
Public health experts say that even as cases go down, contact tracing is one of the keys to controlling COVID-19.
"I really think this is contact tracing's moment, because those original bottlenecks that were preventing us from being able to really impact transmission have been essentially eliminated in most places," said Melissa Boyette, contact tracing technical adviser for the US COVID-19 Response Program with Resolve to Save Lives.
And even with states reopening, some public health departments say their work isn't done -- in fact, they say, the real work to end the pandemic is just now getting started.
The importance of contact tracing
New York City is reopening with over 40% residents fully vaccinated and less than 500 weekly average cases, according to the city's health department.
Dr. Ted Long of NYC COVID-19 Test & Trace Corps said contact tracers are now reaching 97% of cases.
"It's going to be the summer of outbreak hunting," he said.
NYC will be deploying contact tracers with mobile vaccine and testing units to communities with outbreaks for sustained COVID-19 suppression.
Following chains of transmission will lead to the most vulnerable people, "who need vaccines, who need support, who need food packages and cleaning supplies and masks to safely isolate and quarantine," Boyette said.
Dr. Clarence Lam, interim director of occupational health services and the department of health, safety and the environment at Johns Hopkins, said the public should know contact tracing helps protect vaccinated people, too.
"There are breakthrough cases," Lam said. "We know that there are people who have been fully vaccinated who have come down with COVID."
Research shows the vaccines are likely effective against variants, and people who do experience breakthrough infection tend to have mild or no symptoms. However, proponents of contact tracing say it's important to get a better picture of whether vaccinated people who experience breakthrough infections can spread the virus to others -- especially with the emergence of new variants.
"If we have variants that are more infectious, something that seems to work and control transmission in the past may not work in the future," said Dr. Dean Blumberg, chair of pediatric infectious diseases at UC Davis Children's Hospital.
Contact tracing with smartphones
Research from the UK presented in Nature found that cases could decline if more people started using a mobile exposure notification app.
California launched CA Notify, a smartphone-based exposure notification program, in partnership with Google and Apple. The app has been activated by 10.5 million Californians -- less than 30% of the 39.5 million population -- and over 116,000 users visited the CA Notify website after receiving an exposure notification, according to the state's department of health.
"These apps are most effective when there's very high utilization," Boyette said, such as among the closed environment of a college campus.
Boyette also warned that over-reliance on these smartphone applications may leave some people out or give false sense of security in low-use settings.
New research also indicates that current exposure notification apps might not be helpful for people who don't speak English, may be overly complicated, and don't always link to a testing site.
The contact tracing workforce
The White House recently announced that $7.4 billion will be invested in public health workers for pandemic preparedness and response.
Many public health departments now employ thousands of contact tracers in jobs they created during the early months of the pandemic. But as COVID-19 cases continue to decline, some have questioned whether those jobs are here to stay.
Current contact tracing capacity may be more than needed because cases are lower, but that the same workforce could be used to improve overall health in their communities, said Dr. Josh Sharfstein, vice dean for public health practice and community engagement at Johns Hopkins Bloomberg School of Public Health.
According to Long, NYC plans to use its 4,000 contact tracers to establish a NYC Public Health Core to improve public health permanently and sustainably.
Public health experts agree that contact tracing can prevent the past from repeating itself. And Boyette is hopeful, telling ABC News the U.S. could be the next New Zealand or Australia.
"They've been able to keep their numbers totally under control with contact tracing and supportive isolation and quarantine," she said, "and I think this is our shot to get us across the finish line."
Dr. Jade A Cobern, pediatric resident in Baltimore entering the field of preventive medicine, is a contributor to ABC News Medical Unit.
Dr. Jay Bhatt is an internal medicine physician, an instructor at the University of Illinois School of Public Health and an ABC News contributor.
John Brownstein, Ph.D, is an ABC News contributor. He's also the chief innovation officer at Boston Children's Hospital and a professor at Harvard Medical School.