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

Key takeaways:

• COVID-19 vaccines train your immune system to recognize and fight against COVID infections.
• After you get a vaccine, it can take a couple of weeks to build immunity against the virus if you've never had a COVID infection or vaccination before.
• If you've already had COVID infection or a previous vaccine, you could reach immunity sooner - often within 10 days - after getting an updated vaccine.
• Many factors affect how quickly you build immunity after vaccination. And the same goes for the strength of that immunity.

Table of contents

Vaccine effectiveness timeline

How long immunity lasts

How immunity works

Infection vs. vaccine immunity

What affects immunity?

FAQs

Bottom line

References

Prostock-Studio/iStock via Getty Images COVID-19 vaccines are very effective at protecting 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. This can vary from person to person based on their age and other health conditions.

How long does it take to build immunity after the COVID vaccine?

For allCOVID vaccines- whether it's your first vaccine or the updated 2024-2025 dose - it usually takes a couple of weeks to build up immunity.

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 probably build immunityquickerafter getting a COVID vaccine.

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Research suggests that people with a history of COVID infection or vaccination reach peakantibody titerssooner than 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. There are 3 approved COVID vaccines for the 2024-2025 season. Note that the CDCdoesn't recommendone over the other. All should offer good protection and are thought to have similar effectiveness.

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

EXPERT PICKS: WHAT TO READ NEXT

• All about COVID-19 vaccines:Get the latest information onCOVID vaccines, including where to get one.
• Can you get a COVID and flu shot at the same time?Yes, and here are tips to plan when toget vaccinated.
• What to know about vaccine side effects:MostCOVID vaccine side effectsare mild and short-lived. Here are tips to manage them.

Now, people 5 years old and up need only 1 shot of the updated 2024-2025 Pfizer or Moderna vaccine. 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 beeneffectiveat protecting against COVID infection. They'reeven more effectiveat preventing severe outcomes - like hospitalization, severe illness, or death.

It isn't totally clear how long after getting the updated vaccine you'll get maximum protection. With the earlier versions,immunity started to developabout 14 days after the first shot and increased for the first month. The updated vaccines may give you an immune boost even more quickly, but it's not certain when you reach peak immunity.

Novavax The Novavax COVID vaccine is an adjuvanted protein-based vaccine. This is a more traditionalapproach to vaccination.

If you're 12 years old or older, you may opt for theupdated 2024-2025 Novavax vaccine. The number of doses you'll need depends on yourvaccination history. If you've never had a COVID vaccine, you'll need 2 doses (3 weeks apart).

Note:The Johnson & Johnson vaccine isno longer availablein the U.S.

How long does COVID immunity last?

Before answering this question, it's helpful to talk about what it means to have immunity against COVID.

In the early stages of the pandemic, the medical community described immunity as something that could help prevent you from getting sick. After Omicron came onto the scene, vaccines and natural infections no longer provided strong protection against getting sick. But they still offered protection against severe disease from COVID, like hospitalization or death.

So, if you think about immunity as protection against severe illness, both natural and vaccine-induced immunity seem to be holding up pretty well.

A large meta-analysis from 2023 showed that people who had been infected with COVID in the past still had90% protectionagainst severe disease (hospitalization and death) 40 weeks later. This was true for all variants - Ancestral, Alpha, Delta, and Omicron. A similar study looking at vaccine-related immunity found that 6 months later, vaccinated people still had81% protectionagainst severe disease.

Staying current withupdated vaccinescan help increase that immunity to COVID and make it last longer as well. Experts recommend an updated shot for people over 12 years of age if it has been more than 2 months since their last shot.

Note that COVID immunity might not last as long if thelatest COVID strainbecomes very different from the one in the vaccine. The 2024-2025 COVID vaccines arebased onwhich strains were circulating in June of 2024. They're expected to be effective against newer strains as well. But if there's a major mutation and change, it's possible the vaccines will offer less immunity against the newest circulating strains.

Thankfully, there aren't signs of this happening. And in the 2023-2024 season, the COVID vaccines continued to offer protection against newer COVID strains even when new mutations occurred.

How does immunity work?

Immunity refers to how your immune system protects you from different infections, like viruses and bacteria. One way it does this is through white blood cells (immune cells) that circulate in your blood.

Here are some types of white blood cells that play a role increating immunity:

• Macrophagesattack and break down germs when they enter your body. Then they leave behind parts of the germ (antigens), which are then attacked by certain antibodies.
• B lymphocytes (B cells)make antibodies. These are proteins that attack the antigens macrophages left behind. The first time your body is exposed to a certain infection, it can take 7 to 10 days for antibodies to form. But the next time your body is exposed to that infection, your B cells can make these antibodies faster.
• T lymphocytes (T cells)attack cells in your body that have already been infected by the bacteria or virus. After the infection has passed, your body keeps a few T cells, called "memory cells." These cells are ready to fight that infection again if you get exposed to it.

How do you get immunity? Your body can make antibodies and buildimmunityin two ways:

1. Natural immunity:This happens when you get an infection, and your immune system makes antibodies against that infection.
2. Vaccine-induced immunity:This is when your immune system makes antibodies after getting avaccine.

Both types of immunity can last a long time - for years or even longer in some situations.

COVID immunity after infection vs. vaccine

Vaccine-induced immunity and natural immunity both provide protection against future infections. But there are varying reports about which one works better or lasts longer.

Many studieshave weighed in on the side ofnatural immunity. But other studies found that natural and vaccine-induced immunity areequally effectiveagainst the virus that causes COVID.

This is challenging to study because vaccines, boosters, and variants are always changing. Throughout the pandemic, both types of immunity were different with each variant.

Even though it's hard to say for sure which one is better, theevidencegenerally agrees on a few points:

• Protection is limited.Both infection and vaccination greatly reduce the risk of serious infection for at least 10 months -and possibly years. Over time, your protection against mild infectiongoes down.
• Newer variants can better evade immunity.Vaccine-induced and natural immunity gave stronger protection against infection before the arrival of Omicron. Omicron and the strains that came later are better at evading bothvaccineandnaturalimmunity. But there's still strong protection against severe disease with Omicron and later variants.
• People respond in unique ways.Different people are going to have different immune responses to both the vaccine and infection. So, population studies aren't necessarily going to predict an individual's immunity. Neither type of immunity can provide 100% protection against infection.
• Combined natural and vaccine immunity is stronger.Natural immunity along with vaccine immunity provides thestrongest protection. And itdoesn't matterif you get the vaccine before or after natural infection.
• Vaccination is safer than infection.Vaccine immunity comes without the risks associated with natural immunity - like severe infection, hospitalization, or the many complications associated with COVID infection.

What factors can affect COVID immunity?

Different factorscan 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:While all 3 COVID vaccines for 2024-2025 are considered similar in effectiveness, theytarget slightly differentOmicron strains. Moderna and Pfizer target the KP.2 strain, while Novavax targets the JN.1 strain. It's possible that one version may give better immunity, but that's not known yet.
• Weakened immune system:People who areimmunocompromised(those with a weakened immune system from immune-suppressing medications or a health condition) may not develop strong immunity after vaccination.
• Timing of the dose:You can get an updated vaccine if it's been at least 2 months since your last dose. Even if you've been infected with COVID, getting a COVID shot can give you further protection. But the CDC recommends that people at low risk of serious infectionwait 3 monthsbefore getting an updated shot.

Frequently asked questions

Does the COVID vaccine prevent infection? expand_more Yes, all of the approved and updated COVID vaccines canhelp preventCOVID infection. While vaccinations can't prevent all infections, vaccines will help you recover faster and moderate your symptoms.

Does the COVID vaccine wear off? expand_more

How many updated COVID vaccines are there? expand_more

Is the COVID vaccine safe? expand_more

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Researchers are still learning how COVID infection and COVID vaccination affect your immune system and protect against future infections. Your immunity will continue to evolve as the virus does.

The good news is that all 3 of the available COVID vaccines for 2024-2025 offer strong protection against serious illness. If you've had a previous infection or vaccine, you'll probably start building immunity even faster. Vaccination can also give you stronger and longer-lasting protection. So, whether this is your first or sixth COVID vaccine, vaccination can boost your immunity towards the latest strains.

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