The COVID-19 Third Dose and Booster Shot Explained

LUNGevity Foundation
Dr. Amy Moore

Editor's Note: Post was updated on 10/21 with new recommendations and authorizations. 

There has been a lot of information recently about COVID-19 boosters and who should get them and when. Here, LUNGevity’s Dr. Amy Moore, a PhD trained virologist and recognized expert on issues at the intersection of COVID-19 and lung cancer, answers some common questions about boosters and who should get them and when.

What’s the difference between a third dose and a booster shot? Or are they the same? Who should get them?

Third shots and booster shots are NOT the same. We use third shots when talking about an extra shot given to people who may not have achieved an optimal response to their first two shots of either the Pfizer or Moderna vaccine. Third shots are given to those who are considered “immunocompromised,” such as patients with cancer who are on active treatment, those who have undergone organ or bone marrow transplants, those on immunosuppressive drugs, or those with HIV.

Booster shots are given to people who DID have a strong initial response to vaccination (either two shots of Moderna or Pfizer or one shot of J&J) but are now seeing their immune response weaken or fall off. This includes elderly patients (whose immune systems are generally weaker overall), those who got vaccinated very early in the initial roll-out (such as healthcare and other frontline workers), and those who may have other health conditions that put them at increased risk of infection and severe outcomes (for example, those ages 18-64 with heart disease, diabetes, obesity, asthma).

Who should get a third shot or booster shot?

Any immunocompromised patient can get a third dose of either the Moderna or Pfizer vaccine. Medical experts strongly encourage patients with cancer to get a third dose of vaccine at this time. Patients with lung cancer are known to be at increased risk for severe outcomes and death from COVID-19, so they are strongly advised to get vaccinated and to get third shots. Third shots can be given as soon as a month following the second shot.

Boosters were recently approved for those who got Pfizer shots initially. In this case, boosters are recommended for those over age 65, those ages 18 – 64 with other health conditions that put them at increased risk (heart disease, diabetes, asthma, obesity) and those whose jobs or living conditions put them at increased risk (such as healthcare workers). Pfizer boosters use the same amount of mRNA as the first two shots. People falling into the above categories who are at least 6 months out from their second shot should consider getting a booster.

The CDC’s Advisory Committee on Immunization Practices (ACIP) met October 21, 2021 to review the FDA’s newest Emergency Use Authorization regarding Moderna and J&J boosters as well as mixing different vaccine types.

Moderna boosters are recommended for the same categories of individuals as Pfizer boosters: those ages 65 and older; those ages 18 – 64 who are at high risk of severe outcomes because of other health conditions; those whose jobs or living conditions put them at increased risk. While the Pfizer booster contains the same amount of mRNA as the first two doses, the Moderna booster will use half the amount of mRNA as the first two shots. Both Pfizer and Moderna boosters should be given at least 6 months after the second shot.

All individuals ages 18 and older who received the J&J vaccine are encouraged to get a second shot as soon as possible but at least 2 months after the first shot.

This also brings up the idea of mixing vaccine types. The current recommendation is that the first two shots (if getting either Moderna or Pfizer) should be the same. If the same type of vaccine is not available when people go to get a third dose or booster, mixing of vaccine types can be allowed. In this case, some consideration should be given for other risk factors. For example, in young men, where there is a small risk of vaccine-associated myocarditis (heart inflammation) from mRNA vaccines, you could consider getting the J&J shot as a booster. In the case of young women (< 30 years old), where rare blood clots have been associated with the J&J vaccine, it might be worth getting either a Moderna or Pfizer shot as a booster. If you are concerned about your risk for these rare side effects, discuss with your doctor about getting a different type of vaccine for your third shot or booster.

Note that the general public is NOT advised to get boosters at this time. All three vaccines continue to provide strong protection against severe illness, hospitalization, and death. Additionally, our immune response includes protection from antibodies made by B cells as well as cellular immunity from T cells.

Does the need for a booster shot mean the vaccine isn’t effective anymore?

Some people fear that the need for boosters in some groups of people means the COVID-19 vaccines are no longer working. The good news is that all three vaccines currently used in the US remain very strong at protecting against severe illness, hospitalization, and death. However, additional studies from other countries as well as real-world studies in healthcare workers have shown that the vaccines are less effective at blocking against infection and symptomatic illness over time. This is why certain at-risk groups are advised to get a booster shot to “top off” their protection.

What are some side effects of getting a third shot or booster shot?

The Pfizer booster is given at the same dose as the first two shots. The Moderna booster is given at half the dose of the first two shots. Side effects have been reported to be similar to what people experienced originally (headache, swelling/pain at the injection site, fever, aches, fatigue). These are short-lasting.

Can I get my flu shot at the same time as a third dose/booster of the COVID-19 vaccine?

Yes! You may get both shots at the same time, though you may want to get them in different arms.

Can I safely fly cross-country after getting my booster?          

With the holidays rapidly approaching, many wonder how safe air travel is during the ongoing Delta surge of the pandemic. While the signs point to decreasing cases nationwide, we must still use common sense precautions to reduce the chances of getting infected.

Just like with the other COVID-19 shots, you won’t have full protection from the booster until a couple of weeks after your shot. You will want to continue wearing masks in public, maintaining social distance and avoiding crowds and washing your hands or using hand sanitizer often. When flying, you may want to consider upgrading your mask to an N95 or KN95, as these offer the best protection, followed by surgical masks.

That being said, several studies have shown that air travel is relatively safe, even during the ongoing pandemic. Here is some additional guidance regarding travel. The CDC also just updated its holiday guidance, found here.

Will I need to receive the COVID vaccine annually, like the flu shot?

Scientists are still working to determine how often people may have to get a COVID-19 vaccine. The SARS-CoV-2 virus that causes COVID-19 is expected to become “endemic,” meaning it will continue to be present as part of the respiratory viruses that we must deal with each year. It is possible that people will have to get a booster every year or maybe every couple of years. More research is needed to determine how long protection will last for those who have been vaccinated.

To hear the latest on what we know regarding the COVID-19 pandemic and how it affects the lung cancer community, please watch our webinar with leading experts or see our COVID-19 Vaccine FAQs page.

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