The slow roll-out of Covid-19 vaccines – including delayed deliveries, states receiving less than expected doses and problems scheduling appointments – has led to some concern that people are not taking their second dose within the prescribed time frame of 21 or 28 days can not get.
Although 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 pharmacy chains, infectious disease experts and doctors at the forefront of treating patients say there is little room for maneuver for the second dose – while also emphasizing the need to continue to do so. to be vaccinated as soon as possible. if possible.
“There is no maximum interval between the first and second doses for any vaccine,” the CDC said on its website.
Rina Shah, group vice president of pharmacy operations and services at Walgreens, which plans to administer doses across the country in its stores, said that “patients can receive the second dose as long as it follows the immunization window”, which means no earlier than given the designated time frame.
“We encourage patients to schedule the second dose appointment so after the earliest applicable date, but a little after that is OK,” Shah said.
This is contrary to the official guidance of the Food and Drug Administration and Pfizer-BioNTech and Moderna, the drug manufacturers behind the two vaccines currently available in the US, which states that two doses, at specific intervals, are needed for maximum protection . For Pfizer, the interval is 21 days; for Modern, 28 days.
The time frames come from the way the vaccines were administered in clinical trials, which means that the only available data looks at how well the vaccines worked if they were given 21 days for Pfizer and 28 days for Moderna.
But the body’s immune response does not decay 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, said. “It does not forget what was first seen,” he said, referring to the first dose of vaccination.
Creech, who oversaw clinical trials for Moderna, said the vaccines should work as expected, even if the second dose is delayed a month or longer than recommended.
“Do not panic. Even if it is four weeks, six weeks, eight weeks before you can get the second dose, it is good from an immune system point of view,” he said.
The second dose of both the Pfizer and Moderna vaccines serves as a reminder to the immune system.
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“Like any defense mechanism, the immune system can prepare a second time,” said Dr. Bruce Y. Lee, a professor of health policy and management at City University of New York, said. “If you’re exposed to something a second time, it’s telling you, ‘hey, you need to take it seriously.’
This can happen even if the second dose is administered as much as a year later, said Dr. Diane Griffin, an expert in infectious diseases at Johns Hopkins University School of Medicine, said, but there is no data showing that giving the second dose so much later would lead to the 95 percent effectiveness seen in clinical trials. .
“The main reason for the amplifier is to increase the immunity at a high level so that you trust that you are protected,” Griffin said.
Griffin nevertheless stressed the importance of being fully vaccinated sooner rather than later.
“People may think they are protected because they have been given one dose,” she said. Although the first dose provides protection, it should be “emphasized that a second dose is needed” for full protection.
Lee agreed, adding that the better an individual is protected, the better it is for others around them. “If other people are protected, the virus may find fewer opportunities to spread,” he said.
CORRECTION (21 January 2021, 16:51 ET): An earlier version of this article incorrectly indicated the number of days recommended 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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