How Long It Takes For The Coronavirus Vaccine To Work

Are the COVID-19 shots effective right after you get them? Here's the timeline you can expect and other important info to know.

Coronavirus vaccines are finally being administered to people across the country, and with them comes a dose of hope for curbing the pandemic.

Even when you get the vaccine, it’ll take some time for your body to build an immune response that’ll keep you safe and protected. Because of that delay and other unknowns related to the vaccine, doctors are asking people not to let their guard down even after getting vaccinated.

In other words, it’ll take time for the vaccine to kick in, and we should still plan to play it safe after getting the immunizations.

What happens in your body when you get the coronavirus vaccine?

Two of the vaccines, Pfizer and Moderna, use a type of technology called messenger RNA (mRNA). Each jab in the arm essentially includes instructions that teach your body how to fight and destabilize the coronavirus if it comes into contact with it. The one-shot Johnson & Johnson vaccine uses an adenovirus ― the type of virus that causes the common cold ― to teach your body the same thing. Neither of the shots actually cause you to get COVID-19.

“The hope is that when individuals get exposed to the real virus that they can already have pre-formed antibodies to avoid the infection or at least mitigate its severity,” said Onyema Ogbuagu, an infectious disease doctor at Yale Medicine.

It takes time for your body to read those instructions and build up a defense system that can effectively knock out the virus. This process doesn’t happen overnight, so you technically won’t be safe immediately after getting vaccinated.

How long does that process take?

The vaccines from Moderna and Pfizer are two-dose vaccines, meaning you’ll need a second booster shot a few weeks after the first to bring your protection up to a reliable level. If you’re getting Pfizer, you’ll get your shot around 21 days after your first one. Moderna’s second dose is typically scheduled 28 days after the first. You’re considered fully vaccinated about two weeks after you’ve had your second dose. (More on that in a minute.)

“While most people will achieve some level of immunity between two weeks to a month after being vaccinated, a small percentage won’t.”

With a one-dose vaccine, like Johnson & Johnson, it’ll still take your body some time to crack the code and build enough immunity against COVID-19. You’re considered fully vaccinated about two weeks after you get that shot as well.

“When you get a vaccine, usually there is a lag time between when you get the vaccine and when you are protected against the virus. It’s just the time it takes for your immune system to respond to a new antigen [foreign substance] and develop a memory of it to the point where it can ramp that up when it sees a new infection,” Ogbuagu said.

Why are you not protected right away?

The duration and nature of this process can vary depending on the individual.

For starters, not everybody is going to respond to the vaccine. Though most of the vaccines seem to be highly effective, a small but substantial percentage of people won’t respond to them.

The Moderna and Pfizer vaccines are more than 90% effective after receiving both doses. That’s impressive and way more effective than experts predicted early in the pandemic ― but it also means a small group of people who receive these vaccines won’t become immune. And in a population as big as ours, that’s still a significant number of people.

“That still means hundreds of thousands, depending on what [population] scale you’re looking at, could receive the vaccine and not be protected,” Ogbuagu said.

If and when you receive the second dose also affects how long it’ll take for you to become protected. Again, vaccine researchers recommend getting it about three to four weeks after the first dose, depending on which vaccine you get.

If you skip a dose, you won’t be fully protected and could still be at risk for contracting COVID-19. Research on the mRNA vaccines does show that people may wind up being pretty protected after just one dose. But regardless, everyone should definitely get both shots in order to be fully vaccinated.

Furthermore, different factors influence how quickly a person’s immune system responds to a vaccine.

Age is a big one, said Otto Yang, a professor of medicine in the division of infectious diseases and of microbiology, immunology and molecular genetics at the David Geffen School of Medicine at UCLA.

“The very young and very old have trouble making immune responses in general; not that it takes more time, they just cant reach the same [antibody] levels,” Yang said.

Immune-compromising health conditions — like HIV or end-stage renal disease — can also impact how quickly and effectively a person’s body builds immunity after receiving a vaccine, Ogbuagu noted.

It takes about a month on average to be protected from the coronavirus, starting from the day you get the first dose. However, that process can vary from person to person depending on a number of factors.
VioletaStoimenova via Getty Images
It takes about a month on average to be protected from the coronavirus, starting from the day you get the first dose. However, that process can vary from person to person depending on a number of factors.

Keep taking COVID precautions after getting vaccinated.

The truth of the matter is that when we get vaccinated, we’re still going to need to play it safe. While most people will achieve some level of immunity between two weeks to a month after being vaccinated, a small percentage won’t. Depending on your overall health, it also could take your body a little longer to build up a line of defense against the coronavirus.

Researchers are still figuring out how the body uses antibodies and other tools in the immune system to fend off COVID-19, and they don’t yet have all the answers. According to Ogbuagu, we really need to achieve herd immunity — the point at which transmission is reduced because most people have immunity — before it’s really, truly safe enough to return to normal life.

“For this virus, we probably need at least 70% of people to be immune, so that means we’re going to need to achieve a fairly high vaccination rate,” Yang said.

So while there’s a solid chance you’ll be protected once you’re fully vaccinated, we should all still plan to practice COVID-prevention measures ― wearing a mask, avoiding crowded spaces and washing our hands ― until cases begin to dramatically drop.

This article has been updated with new data on the vaccines.

Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.

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