Do COVID-19 vaccines protect against the variants?

By Mayo Clinic Staff

October 7, 2021

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What do I need to know about the delta variant?
Find out about the delta variant and how it spreads, and how a COVID-19 vaccine can protect you.

Nipunie Rajapakse, M.D., Pediatric Infectious Diseases, Mayo Clinic: The delta variant is concerning because it is spread much more easily than prior versions of COVID-19 that we have seen. This means that more people are getting sick. That means more people are getting hospitalized and dying from the infection as well.

The delta variant is concerning because it's more highly transmissible, but the good news is that the COVID-19 vaccine is still highly protective against getting infected or ending up in a hospital or dying from the infection.

Breakthrough infection is a rare event where someone who is fully vaccinated still ends up getting infected with COVID-19. The good news is that these breakthrough infections generally had been asymptomatic or only led to mild illness, and the vaccine remains highly protective against winding up in a hospital or dying from the infection.

The mutations that have caused the delta variant do seem a bit more likely to break through our vaccine immunity as compared to the original types of COVID-19. If you are one of those very rare breakthrough cases that we've been hearing about who still gets infected despite being vaccinated, I want to emphasize those cases are getting a lot of headlines, but they're very rare events and they are not what is driving the current surge in cases that we're seeing. The current surge is really amongst unvaccinated people, predominantly your and middle aged.

If a vaccinated person, gets infected with COVID-19, it is possible for them to transmit it to others. Thankfully, the vaccine significantly reduce your risk of getting infected, which then reduces your risk of passing it on, but yes, it is possible and there are still studies being done to understand exactly how that risk compares with people who are unvaccinated.

Knowing that in rare cases a vaccinated person can transmit COVID-19 to someone else is one of the primary reasons behind the recommendation that vaccinated people now continue to wear a mask if they are indoors in areas where we are seeing a lot of virus circulation. Guidance on masking has changed with the delta variant for a number of reasons. One is that the variant is highly transmissible. It's spread much more easily than prior types of COVID-19 that we have seen and so a layered strategy for prevention becomes even more important so using masks along with vaccination will be more protective than using either alone.

So with the delta variant, we are seeing increased number of cases amongst children. The American Academy of Pediatrics has reported a significant increase in COVID-19 cases amongst people under 18 years of age. So children who are eligible to be vaccinated, which is anyone over 12 years of age, should get vaccinated before returning to school in the fall. It is the single most effective meassure that we will have.

So the best way we can protect kids who can't be vaccinated themselves is to make sure that everyone around them is vaccinated. That means anyone over 12 years of age should go out and get their vaccine, especially before return to school in the fall. Other strategies like wearing a mask when you are out in public, excellent handwashing continues to be incredibly important both for the prevention of COVID-19 and spread of other infections that we're seeing rise in the communities as well these days.

As of right now, there are three vaccines that are approved for use in the United States. Children over 12 years of age are approved for one of the vaccines which is the Pfizer vaccine. So as we've seen, the older part of our population get vaccinated and drive protection from COVID-19, we are seeing that children and young adults are making up a larger proportion of new cases of COVID-19. This is for a variety of reasons. We don't yet have a vaccine that is approved for children under 12 years of age so they are still very vulnerable to getting infected. We also know that vaccine uptake amongst young adults has not been as high as we had hoped, so there is still a large proportion of that population that is still susceptible to getting infected.

If you have not yet been vaccinated, we recommend that you get vaccinated. It is the best thing we have to offer for protection at this point in time.

Key takeaways


In the U.S., the delta (B.1.617.2) variant is now the most common COVID-19 variant. It is nearly twice as contagious as earlier variants and might cause more severe illness. The greatest risk of transmission is among unvaccinated people. But people with vaccine breakthrough infections may also spread COVID-19 to others. However, it appears that vaccinated people spread COVID-19 for a shorter period than do unvaccinated people.

This variant also might reduce the effectiveness of some monoclonal antibody treatments and the antibodies generated by a COVID-19 vaccine.

The alpha, gamma and beta variants continue to be monitored but are spreading at much lower levels in the U.S. The mu variant is also being monitored.

While research suggests that COVID-19 vaccines are slightly less effective against the variants, the vaccines still appear to provide protection against severe COVID-19. For example:

  • Early research from the U.K. suggests that, after full vaccination, the Pfizer-BioNTech COVID-19 vaccine is 88% effective at preventing symptomatic COVID-19 virus caused by the delta variant. The vaccine is 96% effective at preventing severe disease with the COVID-19 virus caused by the delta variant. The research also showed that the vaccine is 93% effective at preventing symptomatic COVID-19 virus caused by the alpha variant.
  • Early research from Canada suggests that, after one dose, the Moderna COVID-19 vaccine is 72% effective at preventing symptomatic COVID-19 virus caused by the delta variant. One dose of the vaccine is also 96% effective at preventing severe disease with the COVID-19 virus caused by the delta variant.
  • The Janssen/Johnson & Johnson COVID-19 vaccine is 85% effective at preventing severe disease with the COVID-19 virus caused by the delta variant, according to data released by Johnson & Johnson.

More about COVID-19 variants and vaccines