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

Vaccine reactions covid 19
Healthcare workers get the Pfizer-BioNTech COVID-19 vaccination at the Legacy Emanuel Medical Center on December 16, 2020 in Portland, Oregon. Paula Bronstein/Getty Images
  • Getting a COVID-19 shot does not make you immediately 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. 
  • Johnson & Johnson’s efficacy was measured 28 days after the single jab. 
  • Visit Business Insider’s homepage for more stories.

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 – not so fast.

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

There are three coronavirus vaccines authorized for use so far in the US. Messenger RNA (mRNA) vaccines from Moderna and Pfizer are given as two separate shots, administered three to four weeks apart. Johnson & Johnson’s new adenovirus vaccine, meanwhile, is administered in a single jab. 

The shots are extremely effective at eliminating severe disease, 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 at least a full month out for J&J’s one shot vaccination, while for Pfizer and Moderna’s two shot course, protection’s not full strength until a week or two after your second dose. 

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.” For Pfizer and Moderna’s vaccines, it’s possible that protection could wane quickly, without a second (booster) shot. 

Here’s precisely how long it takes your vaccination to become near-perfect at preventing severe disease and death from COVID-19, 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. 

If a majority of people choose not to get vaccinated, this disease will continue to spread to healthy people who aren’t vaccinated. That’s why it’ll still be important for everyone 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 of Moderna or Pfizer’s vaccine, 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 on end, because it’s possible that those vaccines won’t work as well then.

This story has been updated to include Johnson & Johnson’s vaccine data. Aria Bendix contributed reporting.