How Soon After the COVID Vaccine Do You Build Immunity, and How Long Does Immunity Last?

COVID-19 vaccines help protect you against severe illness from COVID infection. But after you get a vaccine — or a booster shot — it can take a couple of weeks to build full immunity. The exact timing can vary depending on your age and other health conditions.

How long does it take for the COVID vaccine to work?

COVID vaccines begin to work right away, but it may take a couple weeks for them to build full protection. This is true for all COVID vaccines — whether it’s your first vaccine or a booster.

If you’ve never had COVID or a COVID vaccine in the past, it might take a little longer to reach full protection. But if you’ve had a prior infection or vaccination, you’ll build immunity more quickly after getting a COVID vaccine.

Research suggests that people with a history of COVID infection or vaccination reach peak antibody titers sooner compared to those without — about 10 days after getting their shot. As an added boost, they tend to have three times the amount of antibodies as people with no prior immunity.

While vaccines can’t prevent all COVID infections, they can help keep you safe from more severe illness.

mRNA COVID vaccines

The Pfizer and Moderna vaccines both use messenger RNA (mRNA) technology to stimulate your immune system. Earlier versions of these vaccines required multiple doses. But those versions are no longer in use. 

Now, if you choose to get the updated Pfizer or Moderna vaccine (for people 5 years old and older), it’s only one shot. This is true even if you’ve never had a COVID vaccine before. Guidelines for children (6 months to 4 years old) are a bit different and depend on vaccination history. 

The Pfizer and Moderna vaccines have been effective at protecting against COVID infection. They also help protect against severe outcomes — like hospitalization, severe illness, or death. The bivalent boosters have been even more effective against Omicron variants of the virus. 

It isn’t totally clear how long it takes to reach maximum protection after getting the updated vaccine. Earlier versions showed that immunity started to develop about 14 days after the first shot and increased for the first month. With boosters, the immune response was stronger and quicker (10 days) in people with existing immunity.

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Novavax

The Novavax COVID vaccine uses a protein-based technology with an added ingredient (adjuvant) to boost the immune response. This is a more traditional approach to vaccination.

People 12 years and older can choose the updated Novavax vaccine. The number of doses you’ll need depends on your vaccination history. If you’ve never had a COVID vaccine, you’ll need 2 doses (3 to 8 weeks apart).

Studies suggest the Novavax vaccine builds immunity on a similar timeline to the mRNA vaccines.

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Note: The Johnson & Johnson vaccine is no longer available in the U.S. 

What factors can affect COVID immunity?

Different factors can affect your immune response to a vaccine, including:

• Age: Very young children and older adults may have a lower immune response to vaccines.

• Genetics: Your genes may influence how your immunity responds to certain vaccines.

• Vaccine type: COVID vaccines target certain strains, but the virus evolves over time. This can affect how effective the vaccine is against illness.

• Weakened immune system: People with weakened immune systems (whether from immune-suppressing medications or a health condition) may not develop strong immunity after vaccination. Their protection might also wane more quickly.

• Timing of the dose: Immunity decreases over time (more on this below). If it’s been a while since your last dose, you may be less protected.

How long does the immunity from COVID vaccines last?

Immunity from the COVID vaccine doesn’t last forever — but it also doesn’t disappear overnight. Protection against infection starts to fade after about 3 to 6 months, especially as new variants emerge. That’s why updated vaccines are available each year, similar to the flu shot.

But even as antibody levels go down, your immune system still remembers how to fight the virus. This “immune memory” helps prevent severe illness, hospitalization, and death for much longer — even if you do end up getting sick.

Think of it like this: The vaccine improves how your body recognizes the virus and responds. Your front-line defense (antibodies) might decline over time. But your backup forces (T-cells and B-cells) stick around a lot longer, helping to keep you out of the hospital. 

How long does immunity last after you’ve had a COVID infection?

The length of immunity after a COVID infection depends on the virus variant. But the risk of getting reinfected usually starts to climb after a few months. While COVID antibodies can last up to 6 months or longer, they don’t guarantee you won’t get sick again. This is especially true with new variants in circulation.

The good news is your immune system still “remembers” the virus. This memory helps reduce the risk of severe illness even after antibodies decline. And research supports this. Studies show that people who’ve had COVID are less likely to get seriously ill if they catch it again, especially in the first 3 to 6 months. But just like with vaccines, this protection fades over time.

Getting an updated COVID vaccine can help boost your immunity and keep you protected for longer. This is especially important if you’re at higher risk because of age, pregnancy, or health conditions.

COVID immunity after infection vs. vaccine

Both COVID infection and vaccination can train your immune system to recognize and fight the virus. But they do it in slightly different ways. Infection exposes your body to the entire virus, while vaccines focus on the spike protein. Natural infection may lead to a broader immune response, but it has a greater risk of severe illness, long COVID, or other complications.

So, which is better: immunity from infection or immunity from vaccines? Studies show that both offer strong protection against severe illness, especially in the first few months. But the best protection seems to come from a combination of both — sometimes called “hybrid immunity.” People who have had COVID and are also vaccinated tend to have stronger, more durable immune responses than those who are only vaccinated or only infected. 

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Written by:

Maria Robinson, MD, MBA

Maria Robinson, MD, MBA, is a board-certified dermatologist and dermatopathologist who has practiced dermatology and dermatopathology for over 10 years across private practice, academic, and telehealth settings. She is a fellow of the American Academy of Dermatology and the American Society of Dermatopathology.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. A pulmonologist and hospitalist, she practiced and taught clinical medicine at hospitals in London for a decade before entering a career in health education and technology.

Reviewed by:

Farzon A. Nahvi, MD

Farzon Nahvi, MD, is an emergency medicine physician and author of “Code Gray: Death, Life, and Uncertainty in the ER.” He works at Concord Hospital in Concord, New Hampshire, and teaches at the Geisel School of Medicine at Dartmouth.

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