Medically reviewed by Kasia Hein-Peters, MD, Susan Kerrigan, MD and Marianne Madsen
In late 2020, as the first coronavirus vaccines made their way to market and subsequently into people’s arms, it looked like the beginning of the end of the COVID pandemic. But then, the virus started mutating into several variants, and the so-called Delta variant became the dominant strain worldwide. Despite widespread vaccination campaigns, infection rates skyrocketed. At the same time, scientists discovered that the immunity granted by Pfizer, Moderna, and J&J’s COVID vaccines didn’t last as long as previously thought.
As a result, talk of vaccine booster shots began to circulate. So what exactly is a vaccine booster shot, and how does it help fight COVID-19?
What is a booster shot?
The mRNA COVID vaccines (Pfizer and Moderna) are given in two doses and the J&J vaccine in one dose. At the time, this was deemed sufficient to generate a strong immune response against the virus, and it worked in the short term, keeping many people from contracting the virus. But cases of vaccinated individuals becoming reinfected, either with Delta or with the previous COVID strains, started coming to light over time. Consequently, health authorities have started recommending booster shots to protect against the Delta variant and further reduce the spread of COVID as a whole.
In this case, a booster shot just means an additional dose of the vaccine to strengthen your immunity against the virus. It’s similar to the boosters people get for an MMR vaccine or the same idea as getting a flu shot every year to provide immunity for the variants of the flu.
Why do we need a booster shot?
As vaccine-induced immunity against COVID has been found to wane over time, it means that your chances of getting the virus again, even possibly a symptomatic case, gradually become higher in the months after your initial shots. Furthermore, getting a booster can slow the spread of transmission, since even vaccinated individuals can get (and spread) COVID, but a booster may help these vaccinated individuals by providing an even stronger immune response. While the consensus is still mixed on the necessity of booster shots, it’s clear that they may prove to be a useful tool in finally ending the pandemic.
Regarding the mixed consensus, some governments and health authorities are recommending against booster shots, not because they don’t work, but because they believe that vaccines should first be distributed to developing countries where widespread vaccination has not yet occurred.
Booster shot vs. third dose
There has been some recent confusion regarding the terms “booster” and “third dose.” While the terms are often used interchangeably, they aren’t exactly the same.
A third dose is given to individuals who failed to mount a strong immune response from the first two shots with mRNA vaccines, particularly those with immunocompromising conditions. At-risk individuals often need the third dose as part of their standard vaccine regimen, while in most people, two doses is sufficient.
A booster shot, while also technically a “third dose,” is simply given to protect against new COVID strains like Delta or to “boost” the immune response against the virus–hence the name.
Side effects of the booster shot
Fortunately, the booster shot doesn’t seem to carry any new side effects that weren’t seen in the first two shots. Of course, adverse reactions to any dose of the COVID vaccine can occur, but these are usually mild (soreness at the injection site, fever, chills, headache, or nausea). More serious side effects are rare.
While their necessity has been debated, booster shots have been proven to be effective and may help us make headway in the fight against COVID-19. Soon enough, you might be receiving your COVID booster in conjunction with your yearly flu shot.
UPDATE (as of 11/22/2021)
The FDA and CDC have changed their recommendations for Pfizer and Moderna vaccines:
You should get a booster if you are:
- Ages 50 years and older
- Ages 18 years and older and live in a long-term care setting
You may get a booster if you are:
- Ages 18 years and older
You can get the booster at least six months after completing your primary COVID-19 vaccination series and you can received any of the COVID-19 vaccines authorized in the United States. The CDC recommendations remain the same for the J&J vaccine.
UPDATE (as of 12/16/2021)
In addition to previous recommendations, FDA added a recommendation for teens 16-17 years old who can get a Pfizer booster. All adults 18 years old and above should get a booster with any vaccine, at least 6 months after they got their 2 doses of mRNA or 1 dose of J&J vaccines.
