Do the COVID-19 Vaccines Protect Against Variants?

Microbiologist Esther Babady in her lab

Esther Babady is Director of MSK’s Clinical Microbiology Service.

New data from studies show that the Pfizer-BioNTech COVID-19 vaccine (Comirnaty®), Moderna COVID-19 vaccine, and Johnson & Johnson COVID-19 vaccine are effective at protecting against severe disease caused by harmful variants of the virus.

The most important thing to know right now is that none of the current variants change the way people are tested, diagnosed, treated, or vaccinated.

Esther Babady, Director of MSK’s Clinical Microbiology Service, is a nationally recognized leader in testing for SARS-CoV-2, the virus that causes COVID-19. Here, she answers questions you may have.

If I’m exposed to any of the current variant strains of COVID-19 after I’m vaccinated, will I be protected?

Yes. According to the Centers for Disease Control and Prevention (CDC), the COVID-19 vaccines offer protection against infection by most variants. Most important, they have prevented serious illness, hospitalization, and death, even at a time when new variants are spreading around the world.

COVID-19 Vaccine Information for Patients
Learn what you need to know about the COVID-19 vaccines if you are an MSK patient.
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How do we know which variants are important?

When scientists find variants, it means the virus is changing as it moves through the population. It’s completely normal and expected. The CDC classifies variants into three categories and the WHO proposed using the Greek alphabet to label variants to help with public discussion:

Variants of interest. They may impact transmission, diagnosis, or response to therapy.

  • Epsilon (first identified in California)
  • Eta (United Kingdom and Nigeria)
  • Iota (New York)
  • Kappa (India)
  • Zeta (Brazil)

Variants of concern. In addition to the impact mentioned above, these strains may also lead to more severe illness.

  • Alpha (first identified in the United Kingdom)
  • Beta (South Africa)
  • Delta (India)
  • Gamma (Japan and Brazil)

Variants of high consequence. These strains may not be detected by current tests and may not respond to current therapies or be prevented by current vaccines. Thankfully, no variants of high consequence have been identified in the United States.

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What is the Delta variant and what do I need to know about it?

We have known that the Pfizer-BioNTech, Moderna, and Johnson & Johnson vaccines all provide good protection against most COVID-19 variants. New laboratory studies have tested all three vaccines against the Delta variant and found the vaccines to be effective. Furthermore, observations from different parts of the world suggest that the mRNA vaccines (Pfizer-BioNTech and Moderna) offer good real-world protection against the Delta variant. Most importantly, the reports suggest consistent and high protection from severe disease and hospitalization. This is excellent news.

It is important to remember that the best defense is achieved when you have received all recommended vaccine doses. Partially vaccinated people are less protected and should strongly consider completing their vaccinations as soon as possible to ensure best protection from the Delta and other variants.

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Have MSK patients or staff been infected with a COVID-19 variant after being vaccinated?

Yes, but very few. As of early May, MSK had vaccinated tens of thousands of employees and patients, and had identified fewer than 100 people who experienced a breakthrough infection after the second dose. No vaccine is 100% effective, so this small number of breakthrough infections was expected.

About half of the breakthrough cases were found to have variants, and among those we found a distribution of the different variants. This is good news because it means that at this time, variants are not driving breakthrough infections in vaccinated people. It also means there is not one single variant that’s leading to a greater number of infections after vaccination.

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Will I need to get a booster shot?

Vaccine manufacturers are already working on developing booster shots that will target the variants, but it’s not clear how soon they may be needed.

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When did MSK begin testing for COVID-19 variants?

We have been regularly testing for variants since January 2021 and have processed over 1,000 samples. We look for variants in every patient and staff member who tests positive for COVID-19 unless there’s not enough virus to test.

Testing enables us to detect the frequency of known variants and also determine whether newer, emerging variants are present.

The bottom line is that the faster people are vaccinated, the less chance the virus will have to develop additional variants.


July 8, 2021


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