Chauphuong Ly Dinh, 50, is given a coronavirus disease (COVID-19) vaccination, in Los Angeles, California, April 12, 2021.
Lucy Nicholson | Reuters
White House chief medical advisor Dr. Anthony Fauci on Friday urged Americans to make sure they receive their second dose of the Covid-19 vaccines, saying the second shot provides "dramatic" benefits.
Pfizer's and Moderna's Covid vaccines require two doses given three to four weeks apart. Both vaccines are about 95% effective against the virus, but that strong protection doesn't kick in until two weeks after the second dose, officials say.
Fauci said Friday that about 8% of Americans who received one dose of the Pfizer or Moderna Covid vaccines have not returned for their second shot. But skipping the second dose could cause problems for those Americans, he said, because a single shot of the vaccine triggers a weaker immune response compared with two.
Fauci cited numerous scientific studies, including a Centers for Disease Control and Prevention report published Wednesday that found the Pfizer-BioNTech and Moderna Covid-19 vaccines are 64% effective at preventing hospitalizations in the elderly after one shot, but 94% effective after two doses. The study evaluated 417 hospitalized adults across 14 states from January to March.
"If you're having a two-dose regimen, make sure you're getting that second dose," he said during a White House briefing on the coronavirus pandemic.
Early on, officials and public health experts said they worried it would be difficult for some Americans, especially working-class people who cannot as easily take time off, to return for a second dose. Still, officials have said the uptake of second shots is better than expected.
On Friday, Fauci also urged health-care providers to make sure they quickly reschedule canceled visits for second shots.
Fauci's remarks come as the U.S. is experiencing its first true slowdown in the rate of daily vaccinations after months of a steady climb. The country is averaging 2.6 million reported vaccinations per day over the past week, CDC data shows, down from a peak of 3.4 million reported shots per day on April 13.
His comments also come as the U.S. is tracking highly contagious new variants of the virus. Fauci has previously said two doses of Pfizer's or Moderna's Covid vaccines are better than one to protect against variants.
Earlier this month, Fauci offered advice for those who have reported being diagnosed with Covid after receiving their first vaccine shot and before receiving their second shot.
He said people who get infected with the coronavirus between Covid-19 vaccine shots can get their second dose after they've recovered from the illness and are no longer considered contagious.
– CNBC's Nate Rattner contributed to this report.