Maria Robinson, MDMaria Robinson, MD, is a board-certified dermatologist and medical writer with an interest in nutrition and its impact on health and disease prevention.May 27, 2021, 7:55AM (PT)
Key takeaways:
- COVID-19 vaccines are very effective in building immunity against infections.
- Full immunity can take several weeks after getting your vaccine.
- Different factors can affect how you build immunity to vaccines.
The three COVID-19 vaccines available in the U.S. — Pfizer-BioNTech, Moderna, and Johnson & Johnson – are all very effective in protecting you against getting infected with COVID-19. For each of them, it can take a couple of weeks after the shot to build full immunity. Because the vaccines are relatively new, we are still learning about how long that immunity will last.
Here we’ll discuss how immunity works, what factors can influence it, and when you can expect to build immunity after getting your COVID-19 vaccine.
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 (also called immune cells) circulating in your blood. The main types of white blood cells are listed below.
- Macrophages attack and break down germs when they enter your body. After this, they leave behind parts of the germ (called antigens), which are then attacked by certain antibodies (see below).
- B lymphocytes (also called B cells) produce different types of antibodies, which are proteins that attack antigens left behind by macrophages. The first time the body is exposed to a certain infection, it can take 7 to 10 days for antibodies to form, and they are specific to that infection. The next time your body gets that infection, your B cells will quickly make those specific antibodies to fight the infection.
- T lymphocytes (also called T cells) attack cells in the 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, that are ready to fight that infection again if you get it.
How do you get immunity?
There are two ways your body can make antibodies and get immunity:
- Natural immunity happens when you get an infection, and your immune system starts producing antibodies against that infection.
- Vaccine-induced immunity happens when your immune system starts making antibodies after getting a vaccine.
Both types of immunity can last for a long time — for years and even longer in some situations.
How does immunity from a vaccine compare to immunity from infection?
Vaccine-induced immunity and natural immunity both provide protection against getting the infection in the future. Which one provides better immunity can depend on the type of infection it is.
We are still learning about COVID-19 and immunity, but a recent study showed that vaccine-induced immunity was better than natural immunity in protecting against COVID-19. Getting the vaccine also allowed the immune system to recognize other coronavirus strains, which could provide protection against new variants that develop.
An important advantage of any vaccine-induced immunity is that you can get immunity without actually getting sick. For COVID-19, this is especially important because even if you recover from it, many people continue to have debilitating symptoms for months.
How long does it take to build immunity after I’m vaccinated?
For all three COVID-19 vaccines, full immunity can take a couple of weeks to build. Here we’ll review some differences between the vaccines, but for all of them, it’s important to wait the recommended amount of time after getting the shot(s) before you can be considered fully vaccinated.
Immunity after first dose vs. second dose of Pfizer and Moderna vaccines
The Pfizer and Moderna vaccines are similar in that they both use a new technology called mRNA (messenger RNA) to stimulate your immune system and they both require two shots. Their levels of immunity during clinical trials (as measured by preventing COVID-19 infections) were also somewhat similar.
Pfizer vaccine
- Immunity starts to develop about 12 days after the first shot (at which point the vaccine is about 52% effective).
- Full immunity is reached about 7 days after the second shot (at which point the vaccine is about 95% effective).
Moderna vaccine
- Immunity starts to develop about 14 days after the first shot (at which point the vaccine is about 51% effective).
- Full immunity is reached about 14 days after the second shot (at which point the vaccine is about 94% effective).
As more studies are being done, we’ll learn more about how effective these vaccines are after each of the doses.
Immunity after Johnson & Johnson vaccine
The Johnson & Johnson vaccine is a viral vector vaccine, which works differently than the Pfizer and Moderna vaccines. It only requires one shot.
In the initial clinical trial studies for the Johnson & Johnson vaccine:
- Partial immunity started to develop 2 weeks after the shot, and full immunity was reached about 28 days after the shot, for the overall effectiveness of preventing 66.1% cases of moderate to severe COVID-19 (or 72% if you just looked at people studied in the U.S.).
Additional studies are still providing more information about immunity after the Johnson & Johnson vaccine. For example, some initial studies showed that the immune response may even continue to rise after 28 days.
Factors that can affect immunity
There are different factors that can affect your immune response to a vaccine. Some examples include:
- Age: Very young children and older adults may have a decreased response to vaccines.
- Genetics: Your genes may influence how you respond to certain vaccines.
- Vaccine type: Some vaccines don’t provide as much immunity as others, so booster shots may be needed.
- Health conditions: Certain conditions, like celiac disease and diabetes, may lower your response to vaccines.
- Being immunocompromised: People with a weakened or suppressed immune system may not develop strong immunity after vaccination.
How long does immunity last?
We are still learning about how long COVID-19 immunity lasts, whether you get it from a previous infection or the vaccine.
Vaccine-induced immunity
The COVID-19 vaccines are all pretty new. The first clinical trials for the Pfizer-BioNTech and Moderna vaccines started only about 10 months ago, and Johnson & Johnson began after that. So we don’t have a lot of follow-up data on any of the vaccines yet.
So far, preliminary studies show that people who got the Pfizer and Moderna vaccines still had strong immunity 6 months after the second dose.
All three vaccines are still being monitored and studied. As more time goes on, we’ll have more information on how long their immunity lasts.
Natural immunity
We’re also still learning about how long natural immunity to COVID-19 lasts.
Preliminary studies show that people who recovered from a COVID-19 infection can have immunity that lasts 6 to 8 months. But some studies also show between 20% to 30% of those who had the virus can lose immunity after a 6-month period. This is why it’s still important to get vaccinated against COVID-19 even if you’ve had the infection in the past.
Do I still need to take precautions if I’m vaccinated?
Yes, you’ll still need to take precautions but not as many as before. Remember, not everyone has been vaccinated and COVID-19 is still spreading in some areas.
If you are fully vaccinated — meaning it’s been at least 2 weeks since your last COVID-19 dose — you can now participate in some activities that you did prior to the pandemic.
The Centers for Disease Control and Prevention periodically updates their guidelines on what fully vaccinated people can do. For example:
- If you are around other fully vaccinated people, you don’t need to wear a mask or socially distance yourself in small indoor or outdoor gatherings (except if required by other local law or business guidelines).
- If you travel in the U.S., you don’t need to get tested before or after travel.
- You can eat at an indoor restaurant or bar.
You should still wear a mask when traveling on public transportation and watch out for COVID-19 symptoms if you’ve been around someone who is sick.
Vaccines work well but are not 100% effective, and people who have been vaccinated can still get sick. Fortunately, these COVID-19 “breakthrough cases” are very rare and the vaccine helps prevent more serious illnesses.
The bottom line
We are still learning a lot about COVID-19 and the vaccines. We do know that the COVID-19 vaccines are highly effective in building immunity and protecting you against infection, but full immunity can take a couple of weeks to develop after you get the shot. More research needs to be done to see how long immunity to COVID-19 and the vaccines last.
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