CDC extends time between vaccine doses

The Centers for Disease Control and Prevention has extended the period between the two doses of the coronavirus vaccine people need, which doctors say could help more people receive the initial dose.

The CDC changed its recommendation on vaccine dosing Thursday, saying that second doses of the Moderna and Pfizer vaccines can be given up to six weeks after the first. Previously, people were told they should receive the second dose of the Moderna vaccine within 28 days of the first, and second dose of the Pfizer should be administered within 21 days.

“Extending the time is a reasonable thing to do,” said Dr. David Hamer, an attending physician at Boston Medical Center and professor of global health and medicine at Boston University.

In clinical trials, one dose of Moderna’s vaccine had a 95.2% effectiveness rate after two weeks, according to a Dec. 30 article in the New England Journal of Medicine.

“Extending the time between doses should not lead to any problems in terms of immune response,” Hamer said. “And it will buy us more time to have more people receive their first dose, giving them a chance to have early protection against viral infection.”

Dr. Todd Ellerin, director of infectious diseases at South Shore Health, sounded a more cautious note.

“From the clinical trials, we know that one week doesn’t really make a difference; patients should still get a robust immune response because I think our immune system is smart enough to respond in the way it did during the clinical trials,” Ellerin said.

“But beyond that, it becomes more of an uncontrolled experiment.”

Delaying the second dose does have advantages, however, he said.

“It allows companies to produce more of the vaccine,” Ellerin said. “And if you can space out the second dose a couple of weeks, that takes a little pressure off hospitals.”