Why is a second dose of the COVID-19 vaccine necessary?

The Food and Drug Administration (FDA) will decide whether to grant approval this week for a COVID-19 vaccine, but one big thing: You’ll need to get two doses in order for the vaccine to work.

With every day seeming to break new records for hospitalizations and deaths, COVID-19 is now the No. 1 killer in the U.S, according to the Institute for Health Metrics and Evaluation.

“These are really very, very disturbing numbers. That’s not the time to throw our hands up and say, well, you know, we’re helpless. We’re not.” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

Fauci says help is just around the corner.

“We’re going to start distributing vaccine doses to health care providers and people in nursing homes and other facilities literally within a week or two. It will be in the middle or end of December and then as we get into January, there will be more doses for more people.”

While highly effective, both vaccines – from Pfizer and Moderna – up for emergency authorization require two doses given weeks apart.

“The only way that we have been able to demonstrate that these are effective is if two shots are taken,” said Dr. Marissa Levine.

Levine, director of the Center for Leadership in Public Health Practice at USF, says that’s because of how our bodies react to foreign substances, like vaccines.

“When we first see something that’s foreign to our body, we kind of prime our system, if you will. The second time we see it is when we actually get that boost of immunity.”

But if you skip – or forget – to get your second dose, are you worse off than if you hadn’t gotten vaccinated at all?

“The worst thing is you might think you’re protected when you’re not, and you might let your guard down,” which means you could let the virus in.

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