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, itll take some time for your body to build an immune response thatll 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, itll 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 doesnt happen overnight, so you technically wont be safe immediately after getting vaccinated.

How long does that process take?

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

With a one-dose vaccine, like Johnson & Johnson, itll still take your body some time to crack the code and build enough immunity against COVID-19. Youre 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. Its 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 wont respond to them.

The Moderna and Pfizer vaccines are more than 90% effective after receiving both doses. Thats 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 wont become immune. And in a population as big as ours, thats still a significant number of people.

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

If and when you receive the second dose also affects how long itll 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 wont 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 persons 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 persons body builds immunity after receiving a vaccine, Ogbuagu noted.