Is a COVID-19 Booster Still Effective If You Waited Too Long to Get One?

Hands reaching for the COVID booster shot vial.

Ellen Lindner / Verywell

Key Takeaways

  • If you delay getting a COVID-19 booster shot beyond the recommended time frame from the CDC, health experts say getting it now will still provide protection.
  • Booster shots trick the immune system into thinking there’s a pathogen/virus, which will then activate antibody cells and other immune cells to remove pathogens from the body. 
  • More studies are needed to determine exactly how effective booster shots will be after a certain time period, in addition to how variants may impact the level of effectiveness.

Getting vaccinated against COVID-19 is one of the most important life-saving tools we have in this pandemic and vaccines have been proven to be safe and effective.

Despite this, healthcare records from the United States, United Kingdom, and Israel have shown COVID vaccine immunity wanes over time. Instead of offering around 90% of protection against mild cases of the disease, it may be only 70% effective after six or seven months.

Due to some of these findings, the Centers for Disease Control and Prevention (CDC) recommended COVID-19 booster shots for most people, at least two months after the primary dose of the Johnson & Johnson vaccine and five months after Pfizer or Moderna.

However, if you completed your initial vaccine series, but never got a COVID-19 booster shot during the recommended time frame from the CDC, will you still get protection from the booster shot and how effective will it be?

Why Is There a Wait Period for Booster Shots?

Even if people wait beyond the recommended time frame from the CDC to get a COVID-19 booster shot, the vaccine will still be very effective, Sharon Nachman, MD, chief of the division of pediatric infectious diseases at Stony Brook Children’s Hospital, told Verywell. 

“The booster at any time will be incredibly effective, because the focus of it, the role of a booster dose is actually to not get a primary immune response, but a boost response,” Nachman said. “You can get that even a year after your vaccine and still get some bang for your buck.”

She explained that those who wait to get a booster shot months or even years after completing their initial vaccine series will still get protection, because boosters are meant to increase levels of immune response after they have naturally waned over time.

This process can be seen similarly to the tetanus vaccine which protects against diphtheria (difficulty breathing, heart failure, and paralysis), tetanus (which can cause a person’s neck and jaw muscles to lock, making it difficult to open the mouth or swallow), and pertussis (whooping cough or violent coughing).

According to the CDC, five doses of the tetanus shot are recommended for children at two months, four months, six months, 15 to 18 months, and four to six years of age. A booster shot is also recommended at 11 to 12 years of age and for adults every 10 years.

“If you got a diphtheria, tetanus, pertussis vaccine as an infant, in the past we thought, you got your primary series, you’re done,” Nachman explained. “But over the past several years, we’ve said, actually that’s not enough and now there’s a Tdap booster at age 11 [or] 12. So all those kids who we really thought are probably protected, we’ve actually decided to go and boost them seven years later, and they make a wonderful immune response.”

In addition, Nachman said a booster shot tricks the immune system into thinking that it is again seeing a pathogen, which is a microorganism that causes disease. When the body detects a pathogen, antibody-producing cells and other immune cells are called back to recognize specific pathogens and remove them from the body.

Rob Rohatsch, MD, emergency medicine physician and chief medical officer at Solv Health, told Verywell that studies have also shown that while immune protection begins to fade after four to five months, protection is still present even if the booster was received after the 5-month wait period. “I am not aware of a specific study that shows waiting past the 5-month mark causes any harm,” he said. 

How Effective Will Booster Shots Be if You Wait Too Long?

According to Nachman, there’s not enough data at this time to say exactly how effective boosters will be if an individual waits more than five months to get boosted after completing their initial vaccine series.

More studies that look at different time frames will be needed to determine the level of effectiveness of boosters at providing protection, Nachman said. Further research is also necessary to find out how new variants could have an impact on protection.

“In general, yes, it’s good to get boosted even if it’s a year later because you will still get some immune response. Will it be as good as if you had gotten it in six months? Probably not,” Nachman said. “On the other hand, will it still be protective against hospitalizations? Yes. So there’s no downside to getting a booster even if it’s delayed.”

Javeed Siddiqui, MD, MPH, an infectious disease specialist and chief medical officer at TeleMed2U, based in California, told Verywell even though clinical scenarios involving a delayed booster shot for a certain time was not studied in clinical trials, “we know there will be an increase in immunity with a subsequent booster dose regardless of the time frame.”

However, Siddiqui said the main caveat is that by waiting one year after the initial vaccination, we cannot predict what that increase in immunity will be.

“Vaccine is meant to decrease the need for hospitalization and decrease deaths, it is not to provide 100% protection against infection,” Siddiqui said. “This is why we need to continue public health measures such as wearing a mask, social distancing and avoiding mass gatherings.”

Rohatsch added that while we may not know the answers to how effective booster shots will be after waiting certain time periods, “for now, we know that following the CDC recommended guidelines affords the proper protection.”

What About Second Booster Shots? 

The CDC expanded eligibility for a second booster dose for individuals who may be at higher risk of severe outcomes from COVID-19 on March 29. Adults ages 50 and older, as well as people ages 12 years and older who are immunocompromised can receive a second booster shot. 

If these individuals wait beyond the recommended time frame to receive a second booster shot, will they still receive protection? 

According to Nachman, while the answer should be yes, there’s not enough data per population over certain months to give a scientifically based answer.

“We just don’t have enough data on those specific populations who took it early versus late to say how effective the second booster will be, especially if delayed,” she said. “Because remember, the fourth booster dose really didn’t get approved until relatively recently for certain populations.”

Nachman added that patients who are immunocompromised or older are less likely to have a robust immune response to the primary vaccine series and to any boosters.

“Generally when you get older, your immune response is just not as good. I hesitate to compare older adults to cars, but when you buy a new car, it’s going to do a whole lot better on gas mileage than if you have had the car for over 25 years,” Nachman said.

Even though scientists are still learning more about the timing and effectiveness of booster shots, it is better to follow the current recommended schedule for vaccinations and boosters, Rohatsch said.

What This Means For You

If you complete your initial COVID-19 vaccine series but delay getting a booster shot beyond the recommended time frame, health experts say the booster should still provide protection and elicit an immune response.

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.

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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.
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By Alyssa Hui
Alyssa Hui is a St. Louis-based health and science news writer. She was the 2020 recipient of the Midwest Broadcast Journalists Association Jack Shelley Award.