The Need for COVID-19 Booster Shots

Any individual age 5 or older is eligible for a COVID-19 booster shot five months after they were fully vaccinated. There are several reasons to get the booster.

May. 20, 2022 5   min read

More than 66 percent of all Americans are fully vaccinated as of late May 2022, according to CDC data. Being fully vaccinated means receiving two doses of the Pfizer-BioNTech or Moderna vaccine or one dose of the Janssen (Johnson & Johnson) vaccine.

At the same time, just 46.4 percent of those fully vaccinated individuals received a booster shot – despite more than half of them being eligible to receive one.

So what are the reasons to get a booster shot? Scott Stratton Smith, MD, is a Family Medicine physician with Rochester Regional Health and provides an explanation as to why fully vaccinated people need the booster shot.

What is a booster shot?

A booster shot is administered as an additional dose of a vaccine to give a person’s immune system additional protection against a specific type of illness – e.g., influenza, polio, COVID-19, etc.

Depending on the initial dose(s) of the vaccine and how effective it is, health providers may need to give another dose of the vaccine to help ‘boost’ a person’s immune system.

Generally, a booster shot is given to someone after their initial immunity to a disease starts to drop off over time. The booster shot does what its name suggests: it gives a boost to the immune system and helps it continue protecting the body against infection.

”The booster doses work exactly the same as the initial series of shots,” Dr. Stratton Smith said. “Individuals get the dose of the vaccine, it heads to your cells and triggers an antibody response, and if they are exposed to the virus at any point, it will recognize the virus and activate antibodies to fight off the virus.”

Levels of protection

The intent of the COVID-19 vaccines is to prevent infection from the virus as much as possible; the booster dose helps the body’s immune system to prevent hospitalization, severe illness, and death.

There are different reasons why individuals should receive a booster dose, both those who are fully vaccinated and those who have compromised immune systems.

Fully vaccinated

Anyone who receives two doses of the Pfizer-BioNTech or Moderna COVID-19 vaccine, or one dose of the Janssen (Johnson & Johnson) COVID-19 vaccine is considered fully vaccinated two weeks after they were given their last dose.

The body’s immune response to a potential COVID-19 infection decreases over time, so after five months, people who are fully vaccinated should get a booster dose to give their body the opportunity at a better response.

According to a recent CDC study, the Pfizer-BioNTech and Moderna vaccines were 57 percent effective for those who received their second dose more than six months when it came to preventing hospitalization with the Omicron variant. With the booster dose, the protection was found to be 90 percent.


The CDC and FDA recommend a third and fourth dose of the Pfizer or Moderna COVID-19 vaccine be given to people with “moderately to severely compromised immune systems.” Some of these immunocompromised people include:

  • Those undergoing active cancer treatment for tumors or blood cancers
  • Stem cell transplant recipients – either within the last 2 years or currently on immunosuppressant medicines
  • Organ transplant recipients taking immunosuppressant medicines
  • Patients with moderate or severe primary immunodeficiency
  • Patients with advanced or untreated HIV infection
  • Those currently being treated with high-dose corticosteroids or other drugs that may suppress your immune response 
  • Those on medications for bowel conditions such as Krohn’s disease or ulcerative colitis

“These are the patients who need to be first in line to receive a fourth dose or second booster shot,” Dr. Stratton Smith said. “They are the most vulnerable because their immune response to the first series is not as robust as patients whose immune systems are not suppressed.”

Risk of breakthrough infections

While there is not definitive data available yet on COVID-19 breakthrough infections with the Omicron variant of the virus, anecdotal evidence from healthcare providers across the U.S. suggests there were more breakthrough infections than with previous variants of the virus.

At the same time, the CDC report released in late January highlights how successful booster doses are at preventing hospitalization and severe illness. In its analysis of more than 310,000 patients across 10 states from August 2021 to January 2022, individuals who received the booster dose were significantly better protected compared to those who only had their first vaccines series.

“We are seeing patients who are fully vaccinated and boosted coming down with COVID-19,” Dr. Stratton Smith said. “However, generally those patients are not becoming extremely ill. Most of those patients are experiencing symptoms similar to a mild cold. With the Omicron variant, those symptoms are more upper respiratory: sore throats, nasal congestion, and less of the loss of taste and smell.”

Fewer individuals sickened by the Omicron variant are having their breathing affected as badly as previous COVID-19 variants such as Delta. This makes infections less severe for vaccinated individuals.

However, for individuals who are unvaccinated, the virus has more potential to be quite severe compared to people who have been fully vaccinated and boosted. Dr. Stratton Smith said practices are seeing young and healthy patients hospitalized in the ICU on ventilators.

A changing virus

As the world approaches the third year of living through the COVID-19 pandemic, people are growing weary of its involvement in nearly every aspect of our lives.

Some patients struggle with the changing nature of COVID-19 and what the medical community is learning about it. While certainty is something everyone needs, Dr. Stratton Smith encourages everyone to remember how new this virus is to the world. That affects how much information we have about treating it – including the need for a booster shot.

“We have to remember that this is a disease that we have only known about for two years,” Dr. Stratton Smith said. “It’s evolving, our information about it is evolving, and we can only go with the most recent most up to date information and we are learning about this virus as it changes,” Dr. Stratton Smith said. “Some of the information we shared 6-12 months ago has changed because our knowledge has changed.”

For other individuals, they simply may not have thought about getting a booster shot and may not have a specific reason for or against it.

Others may not have heard about its safety and effectiveness – and the need for a booster dose to help your immune system protect against newer variants of the virus. When they have a conversation with their primary care provider about a booster dose, it can often help to put their mind at ease.

Where can I get a booster shot?

Anyone who is fully vaccinated but has not yet received a COVID-19 booster shot can find them at several different locations.

Booster shots are widely available at primary care offices, pharmacies, and clinics run by local public health departments.

For individuals who received the Johnson & Johnson vaccine, doses of the Pfizer-BioNTech and Moderna COVID-19 vaccines are often used a booster. There is evidence that receiving the Johnson & Johnson vaccine first and a booster dose of either the Pfizer or Moderna vaccine second gives a broader protection than two shots of the Johnson & Johnson.

“Like the COVID-19 vaccine itself, booster shots are safe and effective,” Dr. Stratton Smith said. “Any side effects that come with the shot – such as a sore arm, mild fatigue, or body aches – are gone within 12-48 hours. It is so much better than being on a ventilator.”

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