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COVID-19 Boosters: Why You Should Schedule One Now

Vaccine booster

NOTE:  The following information was published Dec. 21, 2021. For current information, please visit

COVID-19 booster shots are now recommended for all individuals 16 and older who have completed their initial vaccine series (six months after the second Pfizer-BioNTech or Moderna vaccine and two months after the initial Janssen/Johnson & Johnson vaccine).

Booster shots are known to provide renewed protection against both the delta and omicron variants of COVID-19, reducing the incidence of infection and protecting against severe disease.

If you’ve already rolled up your sleeve for your initial COVID-19 vaccine series, you may have questions about the booster shots.

To answer key questions about the boosters and their importance, we spoke with infectious disease and internal medicine physician Joseph Yozviak, DO, Chief Medical Officer, Valley Health Partners, who serves as the Lehigh Valley Health Network (LVHN) Principal Investigator for Pfizer’s COVID-19 vaccine booster clinical trial:

Why do we need booster shots?

Yozviak: COVID-19 transmissions continue to occur at very high levels across the world, in our country and in our own community.  This shows that vaccination levels are not currently high enough to stop the spread of COVID-19.

Even though vaccination has been our most effective tool for preventing infection, severe disease, hospitalizations and death, the level of protection from the initial vaccine series falls over time. 

How do booster shots work?

Yozviak: A booster shot, or another dose of a vaccine that was received in the past, is a great way to remind our immune system how to build a response against a specific virus or bacterium. That’s why we need to get tetanus boosters every five to 10 years and one of the reasons why we receive annual influenza vaccines.

COVID-19 vaccines are no different. Getting a booster dose of an mRNA vaccine (Pfizer-BioNTech or Moderna) boosts antibody levels higher and optimizes our protection. This is true regardless of what vaccine series you originally received (it is preferred that people who received the Janssen/Johnson & Johnson vaccine initially receive the Pfizer or Moderna vaccine as their booster).

In studies that have been reported, booster shots have restored vaccine effectiveness in the United States to greater than 90 percent against symptomatic COVID-19.

Does this mean the original vaccines aren’t effective?

Yozviak: They are very effective, even more so than we originally hoped.  

The protection provided by the COVID-19 vaccines against severe illness, hospitalization and death has remained high, even as the more infectious delta variant became responsible for nearly 100% of new COVID-19 cases. 

However, while the initial vaccine series is still effective, a booster shot provides an even higher level of protection. This is especially important as newer variants emerge. In fact, early information on vaccine responses to the omicron variant suggests that booster doses are necessary for maintaining high levels of protection against it.

Are there any health risks from the booster shots?

Yozviak: COVID-19 booster shots are extremely safe. Reported side effects for the vaccines available in the United States are very similar or milder than what people commonly experienced after their initial vaccine series.

Common side effects such as pain, itching or redness at the injection site, fever, headache, tiredness and body aches usually resolve within a day or two.

Some of the booster trials showed a slight increase in the number of people reporting an enlarged lymph node or discomfort in the armpit (typically on the side where they received the vaccine), but these side effects are harmless and are direct signs that the immune system is responding. 

Should you only get a booster shot from the same manufacturer of your original vaccine(s)?

Yozviak: It depends on the vaccine you initially received.  Due to higher vaccine effectiveness of mRNA vaccines (Pfizer-BioNTech and Moderna) and the severity of rare safety issues with the Janssen/Johnson & Johnson vaccine, mRNA vaccines are preferred by the Centers for Disease Control and Prevention. If you received the Pfizer-BioNTech or Moderna vaccine initially, it’s recommended that you get a booster dose from the same manufacturer as their original vaccine series. If you received the Janssen/Johnson & Johnson vaccine initially, you should receive the Pfizer-BioNTech or Moderna vaccine as your booster.

While most of the information we have about booster doses is from people who received all doses from the same manufacturer, there are some data looking at a “mix and match” booster approach (from a trial done at the National Institutes of Health). These data suggest that antibody responses are best with the Pfizer-BioNTech or Moderna vaccine as a booster, regardless of which vaccine was originally received. There were no concerning differences in side effects with this approach, either. However, the number of people in each study group was very small, which makes it difficult to recommend one type of mRNA vaccine booster over another. 

The bottom line is, regardless of which vaccine you originally received, you should get an mRNA vaccine (Pfizer-BioNTech or Moderna) as your booster. 

Will we need more boosters?

Yozviak: It’s too soon to know for sure. There are a lot of factors that will affect the need for additional boosters, including:

  • How much virus is being spread in the community
  • How many people are becoming severely ill and being hospitalized
  • How much and how soon our protection decreases from current boosters
  • How well future variants can evade the immune response from the previous vaccines

The most important thing you can do is get vaccinated and receive any boosters that are needed. If we do that, we can keep COVID-19 infections down, keep our hospitals from filling up and help slow the development of new variants by reducing the virus’s ability to spread.

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