"Modest delays” between first and second doses of Covid-19 vaccine are not expected to decrease protection against the virus, the US Food and Drug Administration told CNN Saturday.
Previously, the agency had warned that changes to vaccine schedules without appropriate data could put public health at risk.
The US Centers for Disease Control and Prevention this week updated its guidance to say second doses of Covid-19 vaccines may be scheduled up to six weeks after initial doses, if necessary. The CDC said that second doses should be administered as close as possible to the recommended interval -- three weeks after the first dose for the Pfizer/BioNTech vaccine and four weeks after the first dose for the Moderna vaccine.
In its statement on Saturday, the FDA said it “recognizes that getting as many people as possible across the country fully immunized will help to curtail the spread of the virus that causes Covid-19 and should be a priority."
“Modest delays in the administration of the second dose, if absolutely necessary, would not be expected to decrease the protection conferred by the second dose and are preferable to not completing the 2-dose series.”
Earlier this month, when concerns about the availability of vaccines prompted suggestions to extend the length of time between doses, FDA officials doubled down on initial recommendations.
“At this time, suggesting changes to the FDA-authorized dosing or schedules of these vaccines is premature and not rooted solidly in the available evidence,” FDA officials wrote on January 4. “Without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from Covid-19.”
Clinical trials showed both vaccines are about 95% effective, when used according to recommended dosages and dosing intervals. The FDA noted that it has not evaluated data regarding the protection provided by the vaccines if there are longer delays in administering the second dose.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN on Friday that he didn’t think it would make a big difference if a person’s second dose took place two or three weeks after the recommended time.
“I don’t see a big problem with that if the situation on the ground means the stress is such you can’t precisely do 28 days or 21 days,” Fauci said.