Now Playing: ABC News Live Update: Early evidence of new variant spreading in NYC

Now Playing: CDC guidelines to reopen schools met with criticism

Now Playing: ABC News Live Update: New COVID variant spreading rapidly through NYC

Now Playing: FDA to meet tomorrow about J&J emergency use authorization

Now Playing: New study suggests plant-based diets reduce risk of heart disease

Now Playing: New COVID variant in NYC

Now Playing: Facing stress from the pandemic, thousands re-examine relationship with alcohol

Now Playing: ABC News Live Prime: Wednesday, February 24, 2021

Now Playing: ABC News Lives Presents Prescriptions for Health: Your Heart and You

Now Playing: What age should you be aware of prevention of heart disease?

Now Playing: The science on halting the gene that causes heart disease

Now Playing: ‘The Queen of Daytime’ shares how early diagnosis and intervention can save lives

Now Playing: What are the risk factors for heart disease in pregnant women?

Now Playing: People of color dealing with not receiving treatment needed for heart disease

Now Playing: What are the telltale signs of heart disease?

Now Playing: Anti-vax sentiment slows Europe’s vaccine rollout

Now Playing: By the Numbers: Children’s mental health crisis during pandemic

Now Playing: Single-dose vaccine effective against COVID-19 variants, data shows

Now Playing: The Johnson & Johnson COVID-19 vaccine could be authorized by Friday

Now Playing: Nursing home residents get 2nd dose of COVID-19 vaccine