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The slow rollout of Covid-19 vaccines – including delayed deliveries, states receiving fewer doses than expected, and difficulty scheduling appointments – has led to dismay that people cannot receive their second dose in the prescribed period of 21 or 28 days.
While potentially worrying, public health experts across the country say there is no cause for concern.
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The Centers for Disease Control and Prevention, national drugstore chains, infectious disease experts and physicians on the front lines of treating patients say there is leeway for this second dose – while stressing that it getting the full vaccine as soon as possible is always essential.
“There is no maximum interval between the first and second dose for either vaccine,” the CDC says on its website.
Rina Shah, group vice president of pharmaceutical operations and services at Walgreens, which plans to deliver doses at its stores across the country, said “patients can receive the second dose as long as it stays within the window of vaccination “, which means that the second dose is given as soon as possible within the allotted time.
“We encourage patients to schedule the second appointment closest to the earliest appropriate date, but a little later it’s OK,” Shah said.
This goes against official guidelines from the Food and Drug Administration and Pfizer-BioNTech and Moderna, the drug makers behind the two vaccines currently available in the United States, which state that two doses, administered to specific intervals, are necessary for maximum protection. For Pfizer, this interval is 21 days; for Moderna, 28 days.
These delays come from the way vaccines were administered in clinical trials, meaning the only data available examines how vaccines work when given 21 days apart for Pfizer and 28 days apart. for Moderna.
But the body’s immune response does not expire after a set interval.
“Your immune system is really smart,” said Dr. Buddy Creech, director of the Vanderbilt Vaccine Research Program at Vanderbilt University Medical Center in Nashville, Tennessee. “He doesn’t forget what he saw the first time,” he said, referring to the first dose of the vaccine.
Creech, who oversaw clinical trials for Moderna, said the vaccines should work as expected, even if the second dose is delayed by a month or more than recommended.
“Don’t panic. Even if it takes four weeks, six weeks, eight weeks before you can get that second dose, it’s all fine with the immune system,” he said.
The second dose of Pfizer and Moderna vaccines serves as a booster to the immune system.
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“Like any defense mechanism, if the immune system sees something once, it can be prepared the second time around,” said Dr Bruce Y. Lee, professor of health policy and management at City University of New York. York. “If you’re exposed to something a second time, it tells you – hey, you’ve got to take it seriously.”
This could happen even if the second dose were given up to a year later, said Dr Diane Griffin, an infectious disease specialist at Johns Hopkins University School of Medicine, although there is no data showing that administration of the second dose much later would lead to a 95% efficacy observed in clinical trials.
“The main reason for the booster is to raise the immunity to a level high enough that you can be sure you are protected,” Griffin said.
Still, Griffin stressed the importance of getting a full vaccine as soon as possible.
“People may think they are protected because they have been given a dose,” she said. While the first dose provides protection, “it should be emphasized that a second dose is needed” for full protection.
Lee agreed, adding that the more protected a person is, the better it is for others around them. “If other people are protected, the virus may find fewer opportunities to spread,” he said.
CORRECTION (Jan. 21, 2021, 4:51 p.m. ET): A previous version of this article incorrectly stated the recommended number of days between each Covid-19 vaccine. The interval for Pfizer is 21 days (not 28), and the interval for Moderna is 28 days (not 21).
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