Why will the COVID-19 vaccine require 2 doses?

SALT LAKE CITY, Utah (ABC4 News) – On Wednesday, officials in Utah laid out a timeline for Utahns to get vaccines for COVID-19 — vaccines that will both require two doses.

“Those two doses, it’s not a booster dose. What it is, you know how if you’re a teenager, or a kid, and you want them to take out the garbage, you want them to wash their hands — you kind of have to tell them more than once? Well, your immune system kind of works the same way,” said Tamara Sheffield, MD, Medical Director for Intermountain Healthcare’s Community Health Health and Prevention.

Sheffield says that dosing twice — at least 21 days for Pfizer’s vaccine, and 28 for Moderna — comes as a result of testing during vaccine trials.

“They tested to see when was the peak time of the amount of antibody that came up in the serum inside your blood. And they found out it was peaking at about 21 days, so they realized — oh, we can go ahead and give that second dose of 21 days,” said Sheffield.

Sheffield further explained the logic behind two doses in the COVID-19 vaccines.

“The reason why we need to make sure we have a sufficient number of doses is to make sure our immune system recognizes the protein or antigen that would cause a disease, and make the antibody to protect you against them. And it takes two doses to get the prime, maximum amount of protection that you need,” said Sheffield.

“There is something within the influenza vaccine that it does compare to. And so for children who are very young – under 9 years – if they’ve never had an influenza vaccine before, they need two doses in that first year. And that’s because the rest of us have been exposed to influenza year after year or the vaccine year after year. And we respond really well to the vaccine. But for kids who are very young, and haven’t been exposed that much to influenza, one dose of influenza vaccine doesn’t give them enough protection. They have to, a month later, have a second dose,” added Sheffield.

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