What to expect after a COVID-19 vaccine, from how long side effects last to when protection kicks in

  • Getting one COVID-19 shot does not make you immune to the coronavirus.
  • Shots from Pfizer and Moderna are designed to be most effective starting 7 to 14 days after the second dose is given. 
  • Even then, it's still possible you could contract the virus, but your odds of getting a severe or deadly case of COVID-19 are almost zero. 
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If you've gotten a COVID-19 shot, congratulations! You're on your way towards some very impressive protection from novel coronavirus infections. 

Over the next few days, you might notice the arm where your vaccine was injected feels sore, and you might feel some fatigue, headache, or other common vaccine side effects.

This is a good sign that the shot is working as planned, and that your body is building up its defenses against the virus.

But, if you're thinking that this new jab in the arm also means you can go ahead and throw your face masks in the trash right away — not so fast.

Protection begins to build 10 to 14 days after the first shot, but it's not full-strength 

The two coronavirus vaccines authorized for use so far in the US, from Moderna and from Pfizer, are given as two separate shots, administered three to four weeks apart.

The shots are extremely effective, and your body will start to develop some protection from infection, beginning somewhere around two weeks after the first one is injected, but that coverage isn't complete until several weeks later, well after the second dose should be scheduled. 

Read More: Answers to your 24 most pressing questions about the coronavirus vaccine, from side effects and costs to when you'll be able to get one

Dr. Anthony Fauci, the country's top infectious disease expert, recently explained to the Harvard Business Review that "you will get some degree of protection, literally within 10 to 14 days" after the first dose, as studies have shown.

But, he stressed "it will not be maximum, and we don't know how durable it would be" without a second shot. 

Here's precisely how long it takes your vaccination to become roughly 95% effective at preventing a symptomatic COVID-19 infection, according to scientific studies of tens of thousands of volunteer vaccine-takers around the world:

These vaccines protect people very well from serious disease and death, but they may not stop the spread

These new vaccines protect people very well from developing symptoms of COVID-19, and they're near-perfect at eliminating death. 

"But if you want to get back to normal, just you or a few other people being vaccinated doesn't change the dynamics of the outbreak," Fauci said. 

It's possible that vaccinated people could still be asymptomatic virus carriers, unwittingly spreading infections around to others in their population. That could be a problem, if a majority of people choose not to get vaccinated, because it could mean that the more deadly and debilitating forms of this disease would continue to spread to healthy people who aren't vaccinated.

That's why it'll still be important to social distance and wear a mask for at least several months to come. 

It's going to take a while to develop herd immunity through vaccination

The good news is that this country, and the world, have conquered diseases like this before: mass inoculating people against deadly and crippling infections including smallpox, polio, and many other now-defunct diseases, which have been wiped out by vaccinations. 

"You can take the most formidable virus, if you have a good vaccine, and essentially box it out," Fauci said. "And that's what we hope to do. So if you want to help, get your friends, your colleagues, and your family to get vaccinated."

And, if you miss your target date for the second shot, worry not. In vaccine trials, not everyone was perfectly on time for their booster dose either, and a few days of lag time shouldn't be an issue. Just don't let the delay drag on for weeks and weeks on end, because it's possible that the vaccine won't work as well then.

Aria Bendix contributed reporting. 

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