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TO BOOST OR NOT TO BOOST: What is the answer?

As of Oct. 22, both the Centers for Disease Control and Prevention and the Western States Scientific Safety Review Workgroup recommended expanding the use of a booster dose of the Pfizer, Moderna and Johnson & Johnson vaccines for eligible populations. The CDC and Western States Workgroup had previously approved the administration of a third dose to boost immunity for vulnerable and immunocompromised groups.

The emergency use authorizations were amended to allow a booster dose of the Moderna COVID-19 vaccine for certain vulnerable populations, six months after completion of their initial vaccination series. Approval also was given for the use of a single booster dose of the Johnson & Johnson COVID-19 vaccine for individuals 18 and over, two months after their single dose. Further, the two organizations cleared the way for the use of a “mix and match” of COVID-19 vaccines which would not require individuals to use the same dose as their initial series.

These approvals follow the FDA’s previous authorization of third dose booster doses for individuals who received the Pfizer-BioNTech COVID-19 vaccine six months after completing their initial series.

In this FAQ, Dr. Dali Fan, a UC Davis Health Science Clinical Professor who also serves as a volunteer vaccinator at California Northstate University in Elk Grove, California, answers some of the most commonly asked questions about boosters.

1) What are the benefits of getting a booster?

FAN: COVID-19 boosters are meant to boost immunity that may have waned overtime and are the same dose of vaccine that were given as part of the primary series. Booster doses of vaccines are very common. They are part of most childhood and adult vaccine series to ensure a person maintains optimal immunity against infection from a disease.

2) What is the difference between an additional dose and a booster dose?

FAN: An additional dose is administered to people with moderately to severely compromised immune systems. This additional dose of an mRNA COVID-19 vaccine is intended to improve immunocompromised people’s response to their initial vaccine series

At this time, CDC does not have a recommendation for immunocompromised people to receive both a booster dose and an additional dose. The current recommendation is for immunocompromised people to receive an additional dose 28-days after completing an mRNA COVID-19 vaccine series.

As you can see, an additional dose is specifically meant for those who are “immunocompromised.” Others do NOT need an additional dose (28 days after the initial series), but they may be eligible for a booster two-to-six months after the initial series depending on the type of vaccine.

3) Are the boosters different than the original vaccination series?

FAN: The boosters are the exact vaccine as the original series for these vaccines.

4) Does the fact that boosters are recommended mean that the vaccines are not effective?

FAN: No. COVID-19 vaccines are working well to prevent severe illness, hospitalization, and death, even against the widely circulating Delta variant. However, public health experts are starting to see reduced protection, especially among certain at-risk populations, against mild and moderate cases of COVID-19.

Vaccine boosters are common, as most of us have had them throughout childhood and adulthood. Whether it is measles, Hepatitis A/B or COVID-19 – boosters are great tools in our arsenals to fight disease.

5) Who is eligible to get a booster dose now?

FAN: A Pfizer or Moderna booster dose is recommended if you:

Received your second dose at least six months ago, and

Are 65 or older, or

Age 18+ who live in long-term care settings, or

Age 18+ who have underlying medical conditions, or

Age 18+ who are at increased risk due to social inequity, or

Age 18+ who work or live in high-risk settings

A Johnson & Johnson booster dose is recommended if you:

Received your first dose of the Johnson & Johnson vaccine at least 2 months ago, and

Are 18 or older

If you fall within the categories above, you can get your booster by going to your healthcare provider, clinics and neighborhood pharmacies. You can visit or call 833-422-4255 to make an appointment or find a nearby vaccine clinic.

5) The CDC has recommended additional does for those over 65, people living in group homes, and the immunocompromised. How do we define who is immunocompromised and needs an additional dose?

FAN: Currently, the CDC is recommending that moderately to severely immunocompromised people receive an additional dose. This includes people who have:

Been receiving active cancer treatment for tumors or cancers of the blood

Received an organ transplant and are taking medicine to suppress the immune system

Received a stem cell transplant within the last 2 years or are taking medicine to suppress the immune system

Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)

Advanced or untreated HIV infection

Active treatment with high-dose corticosteroids or other drugs that may suppress your immune response

People should talk to their healthcare provider about their medical condition, and whether getting an additional dose is appropriate for them.

7) The CDC has also recommended that essential workers might consider getting boosters. Is that your recommendation as well? What types of workers are particularly high-risk?

FAN: Yes, it is my recommendation as well.

Examples of workers who may get Pfizer-BioNTech or Moderna boosters:

First responders (e.g., healthcare workers, firefighters, police, congregate care staff)

Education staff (e.g., teachers, support staff, daycare workers)

Food and agriculture workers

Manufacturing workers

Corrections workers

U.S. Postal Service workers

Public transit workers

Grocery store workers

This list could be updated in the future.

8) Where can we get boosters? And are boosters free?

FAN: Visit the state’s websites at or to learn more about where boosters are being offered near you. Your healthcare provider or local pharmacists can also help connect you to resources. The booster is free of charge to all; no insurance or documentation is required.


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