The U.S. has been rolling out COVID vaccines to its population for just over a month now. As of today, 16.5 million doses have been administered -- 9 million from Pfizer (NYSE:PFE) and its partner BioNTech (NASDAQ:BNTX) and 7 million from Moderna (NASDAQ:MRNA). Both mRNA vaccines have demonstrated exceptionally high efficacy and are hugely important tools in combatting the coronavirus pandemic. 

Considering more than 24 million cases of COVID-19 have been reported in the U.S. since the start of the pandemic, it's natural to ask: "If I already had COVID, do I still need a vaccine?" You do, and here's why:

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