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If a vaccinated person gets infected, it is a sign that they're not immune to the virus?

This article was published on
July 8, 2021

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Someone who is vaccinated shouldn’t think they are absolutely immune, because they can still get what is called a "breakthrough infection" (an infection that happens to someone who is fully vaccinated). Breakthrough infections are relatively rare and CDC guidance says that, typically, ~2 weeks after the full course of COVID-19 vaccination, the body builds some protection (immunity) that can last for at least several months. This protection is highly effective at preventing serious disease, hospitalization, and death. 

Someone who is vaccinated shouldn’t think they are absolutely immune, because they can still get what is called a "breakthrough infection" (an infection that happens to someone who is fully vaccinated). Breakthrough infections are relatively rare and CDC guidance says that, typically, ~2 weeks after the full course of COVID-19 vaccination, the body builds some protection (immunity) that can last for at least several months. This protection is highly effective at preventing serious disease, hospitalization, and death. 

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What our experts say

Research shows that the approved vaccines protect an encouragingly high percent of people from severe disease, hospitalization, and death. The data also suggests that several vaccines remain mostly effective against variants of concern such as Alpha, Beta, and Delta.

However, vaccines are not 100% effective at preventing illness. Someone who is vaccinated shouldn’t think they are absolutely immune, because they can still get what is called a "breakthrough infection" (an infection that happens to someone who is fully vaccinated). Breakthrough infections are relatively rare and CDC guidance says that, typically, ~2 weeks after the full course of COVID-19 vaccination, the body builds some protection (immunity) that can last for at least several months. This protection is highly effective at preventing serious disease, hospitalization, and death. 

For example, Johnson & Johnson submitted preprint studies in July 2021 and in them reported that their vaccine "generated strong, persistent activity against the rapidly spreading Delta variant and other highly prevalent SARS-CoV-2 viral variants. In addition, the data showed that the durability of the immune response lasted through at least eight months, the length of time evaluated to date." In April 2021 Moderna and Pfizer reported that their COVID-19 vaccine protection can last for at least six months.

Peer-reviewed research on the body’s immune response, which was published in the scientific journal Nature, found persistent immune activity over four months after COVID-19 vaccination. Some scientists are exploring whether some parts of our immune activity can help determine if vaccines are lifelong or require boosters.

Research is still being done on longer-term immunity from COVID-19 vaccination.

Many prevention methods we use in our daily lives, ranging from vaccines to condoms, are not 100% effective. But vaccines are widely used because they can protect many people from serious disease. The U.S. Centers for Disease Control and Prevention (CDC) recommends COVID-19 vaccination for everyone who is eligible, and reminds people that "it typically takes 2 weeks after vaccination for the body to build protection (immunity) against the virus that causes COVID-19."

Context and background

Misinformation has been spreading about what it means when a vaccinated person is infected with COVID-19, with some people falsely claiming that this suggests the vaccines are not effective. Approved COVID-19 vaccines have been rigorously tested for efficacy and protect the vast majority of recipients from serious symptoms, hospitalization, and death. Even if a vaccinated person becomes infected, vaccination reduces the likelihood of the infection becoming more severe and deadly.

Resources

  1. Key Things to Know About COVID-19 Vaccines (U.S. Centers for Disease Control and Prevention)
  2. Positive New Data for Johnson & Johnson Single-Shot COVID-19 Vaccine on Activity Against Delta Variant and Long-lasting Durability of Response (Johnson & Johnson)
  3. Moderna Provides a Clinical Update on the Neutralizing Activity of its COVID-19 Vaccine on Emerging Variants Including the Delta Variant First Identified in India (Moderna)
  4. UK study finds vaccines offer high protection against hospitalisation from Delta variant (Reuters)
  5. SARS-CoV-2 mRNA vaccines induce persistent human germinal centre responses (Nature)
  6. COVID-19 vaccine generates immune structures critical for lasting immunity (Washington University in St. Louis)
  7. COVID-19 vaccines likely activate strong, lasting immunity (Futurity)

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