Everything You Need To Know About Breakthrough COVID Infections

A breakthrough COVID-19 infection is when a fully vaccinated person contracts SARS-CoV-2, the COVID-19 virus. As the number of vaccinated people increases, more people will have a breakthrough infection. This article covers COVID-19 vaccination, testing, and when to be concerned about a breakthrough infection.

Breakthrough COVID Infection

Yuichiro Chino / Getty Images

What Is a Breakthrough Infection?

The COVID-19 vaccines are very effective at preventing severe illness and death, but they are not 100% effective at preventing infection. No vaccine is 100% effective at preventing disease.

When a fully vaccinated person contracts SARS-CoV-2 at least two weeks after completing vaccination, it is considered a breakthrough infection.

Fully vaccinated people with a breakthrough infection are less likely to develop severe disease, be hospitalized, or die from COVID-19 compared to unvaccinated people. However, fully vaccinated people with a breakthrough infection can still pass the virus to someone else.

Breakthrough COVID-19 infections are uncommon. Estimates are not accurate at this time and range from 1 in 100 people to 1 in 5,000 people that might develop a breakthrough infection. It is difficult to truly track the number of breakthrough cases because people with mild symptoms are less likely to seek testing or see a healthcare provider.

State health departments, the Centers for Disease Control and Prevention (CDC), and global organizations are still evaluating the data to determine how often breakthrough infections occur. However, they are confident that unvaccinated people are 5.8 times more likely to contract SARS-CoV-2 and test positive for the virus than unvaccinated people.

Antibody Levels

Scientists have determined that the likelihood of a breakthrough infection is higher when antibody levels are low. Therefore, it's essential that people seek vaccination and obtain a COVID-19 booster if available.

If You're Vaccinated, What Warrants a COVID-19 Test?

The symptoms associated with a breakthrough COVID-19 infection are the same in both vaccinated and unvaccinated people, but they are less severe in people who are vaccinated. COVID-19 can cause:

  • Fever
  • Fatigue
  • Cough
  • Sore throat
  • Headache
  • Chills
  • Muscle aches
  • Loss of smell

However, a global study that ranked the most likely symptoms of a breakthrough infection reported that people commonly have headaches, sneezing, runny nose, sore throat, and loss of smell. Notably, in the analysis, people who developed symptoms associated with a breakthrough infection had milder symptoms and a shorter duration of illness.

According to the CDC, you should get tested at least five days after being exposed to COVID-19—even if you don't have symptoms. If you develop symptoms, you should get tested right away.

Best Testing Options for a Breakthrough Case

Several testing options are available, and the possibilities are the same whether a person is vaccinated or unvaccinated.

There are three COVID-19 tests to understand: rapid antigen, molecular nucleic acid (also called PCR or RT-PCR), and antibody tests.

The rapid antigen and molecular PCR tests determine whether someone has an active COVID-19 infection.

Antibody tests are different in that they detect whether a person has been previously infected with, exposed to, or vaccinated against SARS-CoV-2. Antibody tests should not be used to determine whether a person has an active infection and are not helpful in people who have been vaccinated.

There are several factors to consider when deciding which test to obtain. These include:

  • Ability to visit a hospital or clinic versus needing an at-home test
  • Time to results
  • Cost
  • Diagnostic accuracy

Rapid antigen tests are more widely available than other tests. They are offered in hospitals and clinics and can be done at home. Molecular PCR tests are considered the gold standard of COVID-19 tests, and they are most often used in hospitals but are also offered in clinics. One molecular PCR test kit is available for home use.

Rapid antigen tests generally provide a result in about 15 to 30 minutes. Molecular PCR test results usually return after one to two days. At-home molecular PCR test kits usually require a person to send a specimen to a laboratory.

Rapid antigen tests are cheaper than PCR tests; however, they do not have the best diagnostic accuracy.

Know Which Test You Use

Be sure you understand which at-home test you are using to avoid confusion and delays in getting your results.

Factors That Affect Accuracy

Several factors affect COVID-19 testing accuracy, including:

  • Whether a person has symptoms
  • Time from exposure or symptom onset
  • Sample collection method

The amount of virus in a person's system can affect test results. Testing for COVID-19 when a person does not have symptoms increases the possibility of a false-negative result. Researchers report COVID-19 test accuracy in a person with symptoms at approximately 80%, whereas the tests are about 55% accurate in people who do not have symptoms.

Testing too early after exposure can also give a person a false-negative result. In one study, there was a 67% chance of patients receiving a false-negative result if they tested within four days of contracting the virus. If a person waited to test on the day of symptom onset (usually four days after becoming infected), the probability of receiving a false-negative result dropped to 38%.

The researchers explained that testing was most accurate when performed three to four days after symptom onset, but even then, the probability of receiving a false-negative result was 20%.

Finally, the way that a sample is collected can also affect test accuracy. Many people find the nasopharyngeal swab uncomfortable, but, when done correctly, it's the most accurate way to collect a COVID testing sample.

Saliva tests have become more widely available, but the accuracy varies widely because of how the sample is collected. However, researchers have been improving these testing kits and even though they are not quite as accurate as other kits, they still provide better access to testing for those who need it.

Breakthrough COVID-19 and Virus Variants

Several different SARS-CoV-2 variants have spread across the United States, which are being monitored by the CDC.

The Delta variant is currently the most prominent and most concerning since it is more contagious, which means it is also more likely to lead to a breakthrough infection. The Omicron variant is currently undergoing further investigation to determine how mutations affect the likelihood of severe infection.

The FDA-approved antigen and molecular PCR tests detect these variants, including the Delta variant. The Omicron variant is being studied further, but we know that molecular PCR tests detect this new variant.

Additionally, the FDA-authorized vaccines still offer protection against variants, including the Delta variant. Further research needs to be done to determine the effectiveness of vaccines against the new Omicron variant, but it is likely that the vaccines offer some protection against severe COVID-19 and death.

How Long Does It Take to Build Immunity After Getting the COVID-19 Vaccine?

It can take about two weeks to develop immunity to SARS-CoV-2 after vaccination.

The CDC reports that the effectiveness of the mRNA vaccines in people with normal immune systems is 90%. However, people with weakened immune systems might not develop the protection they need against severe COVID-19. The CDC reports that the vaccines are 77% effective in these people.

In addition to certain diseases that lead to decreased immunity, people over age 65 are more likely to have weak immune systems. They may not develop an appropriate immune response to vaccination.

Thus far, reports show that people with weakened immune systems or people over the age of 50 have made up almost 50% of hospitalized breakthrough infections in the U.S. This helps to explain why some older people with breakthrough infections still develop severe disease or death.

Vaccinated people with weak immune systems should continue to practice social distancing and wear masks indoors and in close quarters.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

23 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Ssentongo P, Ssentongo AE, Voleti N, et al. SARS-CoV-2 vaccine effectiveness against infection, symptomatic and severe COVID-19: a systematic review and meta-analysis. BMC Infect Dis. 2022;22(1):439. doi:10.1186/s12879-022-07418-y

  2. Centers for Disease Control and Prevention. Ensuring COVID-19 vaccines work.

  3. Centers for Disease Control and Prevention. Public health investigations of COVID-19 vaccine breakthrough cases: Case investigation protocol.

  4. Centers for Disease Control and Prevention. The possibility of COVID-19 infection after vaccination: breakthrough infections.

  5. Klompas M. Understanding breakthrough infections following mRNA SARS-CoV-2 vaccination. JAMA. 2021;326(20):2018-2020. doi:10.1001/jama.2021.19063

  6. Bergwerk M, Gonen T, Lustig Y, et al. COVID-19 breakthrough infections in vaccinated health care workers. N Engl J Med. 2021;385(16):1474-1484. doi:10.1056/NEJMoa2109072

  7. Centers for Disease Control and Prevention. Rates of COVID-19 cases and deaths by vaccination status.

  8. Centers for Disease Control and Prevention. Symptoms of COVID-19.

  9. Zoe COVID Study. What are the new top 5 COVID symptoms?

  10. Abbasi J. COVID-19 mRNA vaccines blunt breakthrough infection severity. JAMA. 2021;326(6):473. doi:10.1001/jama.2021.12619

  11. Centers for Disease Control and Prevention. Overview of testing for SARS-CoV-2, the virus that causes COVID-19.

  12. Food and Drug Administration. COVID-19 test basics.

  13. Food and Drug Administration. COVID-19 tests and collection kits authorized by the FDA: infographic.

  14. Centers for Disease Control and Prevention. Interim guidance for SARS-CoV-2 testing in nonhealthcare workplaces.

  15. Parvu V, Gary DS, Mann J, et al. Factors that influence the reported sensitivity of rapid antigen testing for SARS-CoV-2. Front Microbiol. 2021;12:714242. doi:10.3389/fmicb.2021.714242

  16. Kucirka LM, Lauer SA, Laeyendecker O, et al. Variation in false-negative rate of reverse transcriptase polymerase chain reaction-based SARS-CoV-2 tests by time since exposure. Ann Intern Med. 2020;173(4):262-267. doi:10.7326/M20-1495

  17. Bastos ML, Perlman-Arrow S, Menzies D, Campbell JR. The sensitivity and costs of testing for SARS-CoV-2 infection with saliva versus nasopharyngeal swabs: a systematic review and meta-analysis. Ann Intern Med. 2021;174(4):501-510. doi:10.7326/M20-6569

  18. Johnson AJ, Zhou S, Hoops SL, et al. Saliva testing is accurate for early-stage and presymptomatic COVID-19. Microbiol Spectr. 2021;9(1):e0008621. doi:10.1128/Spectrum.00086-21

  19. Centers for Disease Control and Prevention. SARS-CoV-2 variant classifications and definitions.

  20. World Health Organization. Update on omicron.

  21. Centers for Disease Control and Prevention. Key things to know about COVID-19 vaccines.

  22. Centers for Disease Control and Prevention. Effectiveness of 2-dose vaccination with mRNA COVID-19 vaccines against COVID-19–associated hospitalizations among immunocompromised adults — nine states, January–September 2021.

  23. Tenforde MW, Patel MM, Ginde AA, et al. Effectiveness of SARS-CoV-2 mRNA vaccines for preventing COVID-19 hospitalizations in the United States. Clin Infect Dis. 2021:ciab687. doi:10.1093/cid/ciab687

By Christine Zink, MD
Dr. Christine Zink, MD, is a board-certified emergency medicine with expertise in the wilderness and global medicine. She completed her medical training at Weill Cornell Medical College and residency in emergency medicine at New York-Presbyterian Hospital. She utilizes 15-years of clinical experience in her medical writing.