Seniors: How Is A COVID-19 Diagnosis Possible After Getting Vaccine?


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This article was updated on May 12, 2021. 

Yes, you can get COVID-19 after the first shot of a two-dose vaccine

Vaccine immunity does not kick in immediately. Most COVID-19 vaccines require two shots, administered several weeks apart, in order to provide people with a robust, long-lasting form of protection against the virus.

Shots that have been approved so far (Pfizer, Moderna, and Johnson & Johnson in the US; Pfizer and AstraZeneca in the UK) have proved highly effective, providing up to 95 percent protection from the disease caused by the novel coronavirus. 

Why not just one vaccine?

Vaccinated people do get some form of protection from their first shot, which generally kicks in after about two weeks. But two shots have been shown to be more effective for stronger, longer-lasting immunity.

“Your body is going to take a little time to build up a robust immune response that is going to provide you protection, and unfortunately, that protection doesn’t come as soon as the needle breaks your skin,” said Dr. Wesley Willeford, Medical Director of Disease Control at the Jefferson County health department in Alabama.

“Once you’re vaccinated, and get both doses, you still need to wait two to four weeks before really beginning to think about re-engaging in a lot of activities.”

Although there is some evidence a first dose can start bolstering the body’s defenses against the novel coronavirus, it’s only after the second shot that your risk of infection can decrease to as little as 5 percent.

It would be a “big mistake” to rely on just one shot of a two-step vaccine to keep you safe from catching COVID-19, said Pfizer CEO Albert Bourla. While one shot could help begin to control the pandemic, Bourla said, “with two, you almost double the protection.”

What we do know is that two shots protect people almost entirely from the most severe, potentially deadly infections.

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Americans receive first-round vaccine, catch COVID-19

Already, there have been several instances of people who have gotten their first shot subsequently getting infected with the novel coronavirus. One nurse in California contracted COVID-19 six days after his first shot, and another emergency-room doctor in Georgia came down with COVID-19 nine days after his first dose of Pfizer’s vaccine.

Vaccine results prove experts right so far

Pfizer-BioNTech’s vaccine is up to 95 percent effective. It consists of two shots that are administered 21 days apart. According to the US Food and Drug Administration, Pfizer’s first shot can provide up to 52 percent protection. But it’s not until a week after the second shot that the chance of falling ill from the coronavirus decreases to just 5 percent. This means if someone receives Pfizer’s two shots exactly 21 days apart, they should not expect to be fully protected until around a month (28 days) after their first dose. 

Moderna’s results look similar. According to trial results, the first shot may provide good protection, around the order of 90 percent, after 14 days. But it’s not clear exactly how long that protection lasts, or how good it really is, because almost everyone in the trials got a second booster shot 28 days later.

The single-shot Johnson & Johnson vaccine is more than 70 percent effective, although it has faced some controversy.

Moral of the story

Get your vaccine as soon as you can, and get BOTH doses. After you receive your first dose, keep social distancing, avoiding large gatherings, wearing a mask, and practicing CDC precautions. Then, be sure to get your second dose, and hopefully, we can beat this virus! Share your vaccination story with others and encourage them to get their shots as well. It starts with you.


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