COVID-19 Vaccine

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Like many other viruses, SARS-CoV-2 — the virus that causes COVID-19 — changes over time. Those changes, or mutations, can lead to new variants of the virus.

There are many variants of SARS-CoV-2 now spreading globally. Scientists are studying them to see how they differ from each other and from the original strain of SARS-CoV-2.

Scientists also are monitoring how well authorized vaccines and therapies that can prevent or treat COVID-19 are working against the variants.

“Because there has been so much transmission globally, it means the virus has had an opportunity to diversify,” says Graham Snyder, MD, medical director, Infection Prevention and Hospital Epidemiology, UPMC. “And when the virus diversifies — when it looks different — that means our immune systems may be less prepared to recognize it.”

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How Many COVID-19 Variants Are There?

Virus mutations are random. It is not unusual for viruses to change over time, Dr. Snyder says. That’s what happened with SARS-CoV-2.

“Every single day, there are hundreds of thousands of transmission events around the world,” Dr. Snyder says. “And when you have hundreds of thousands of transmission events a day, that’s a huge opportunity for something different to emerge.”

There are many variants of the coronavirus spreading globally and within the United States. The Centers for Disease Control and Prevention (CDC) classifies variants into three groups:

  • Variants of interest (VOI): Variants that potentially may cause higher transmission, more severe illness, or may affect existing therapies or vaccines. Variants classified as VOIs may have caused clusters of cases. However, few of these variants have appeared in the U.S. or other countries.
  • Variants of concern (VOC): Variants that have shown some evidence of causing more severe illness or higher transmission rates, or that have shown some evidence of affecting existing vaccines or therapies.
  • Variants of high consequence: Variants that have shown clear evidence of impacting the effectiveness of vaccines or therapies. They also have shown evidence of causing more severe illness and increased hospitalizations.

There are currently no variants of high consequence in the U.S. The CDC is currently tracking several variants of interest or variants of concern.

The most widely known variant of concern is the Omicron variant (B.1.1.529).

Variants differ from each other in transmissibility and severity.

“These emerging strains are likely to be more transmissible,” Dr. Snyder says. “They may be more likely to cause severe disease. For the most part, the strains that we’re seeing, we’re still well prepared to respond to them.”

Does the COVID-19 Vaccine Work Against Variants?

There are currently four COVID-19 vaccines being distributed in the United States: from Pfizer-BioNTech, Moderna, Novavax, and Johnson & Johnson/Janssen (J&J). COVID-19 variants may affect their overall effectiveness. But all vaccines are safe and effective against COVID-19, especially in preventing severe illness, hospitalization, and death.

Vaccines may lose effectiveness over time or as variants emerge. Some people, such as those with compromised immune systems, may not have a strong response to the vaccine.

To combat that, the FDA and CDC have authorized additional and booster doses of the COVID-19 vaccine for many people who have completed their initial series of the vaccine. To view recommendations for additional and booster doses, visit the CDC’s website.

Scheduling an additional dose? Don’t forget to bring your COVID-19 vaccine card with you to your appointment.

Early data on Omicron indicated that the initial doses of the COVID-19 vaccine were not as effective in preventing infection, although they were still effective in preventing severe illness. Additional or booster doses showed a higher level of protection against Omicron.

The CDC recommends people who are eligible for the vaccine get vaccinated and get boosted. To schedule a vaccine or booster appointment at UPMC, visit

“If you’re worried about emerging variants, the most important thing you can do is not give them a chance to transmit,” Dr. Snyder says. “It’s still wise to get the vaccines because they work against what we’re likely to see in the U.S. in the future.”

Scientists will continue to monitor how effective the vaccines are against variants.

Do Monoclonal Antibodies Work Against COVID-19 Variants?

Monoclonal antibodies — which act like your body’s natural antibodies but are created by scientists — are a promising treatment for COVID-19.

So far, the Food and Drug Administration has authorized multiple monoclonal antibody therapies to treat COVID-19.

Monoclonal antibodies have shown great success in preventing severe illness, hospitalization, and death if given shortly after infection. Some monoclonal antibody treatments are more effective against certain variants, and doctors will adjust treatment plans accordingly.

Scientists continue to monitor current COVID-19 variants and will monitor others that emerge. As they learn more information, it could affect guidelines for COVID-19 vaccination and/or treatment.

Visit to learn more about UPMC’s response to COVID-19. Go to to schedule a COVID-19 vaccine appointment with UPMC if you are eligible to receive one.

Editor's Note: This article was originally published on , and was last reviewed on .

Centers for Disease Control and Prevention, About Variants of the Virus that Causes COVID-19. Link

Centers for Disease Control and Prevention, SARS-CoV-2 Variant Classifications and Definitions. Link

Centers for Disease Control and Prevention, COVID-19 Data Tracker, Variant Proportions. Link

Dan Frampton, PhD, et al, The Lancet: Infectious Diseases, Genomic Characteristics and Clinical Effect of the Emergent SARS-CoV-2 B.1.1.7 Lineage in London, UK: A Whole-Genome Sequencing and Hospital-Based Cohort Study. Link

Moderna, Moderna COVID-19 Vaccine Retains Neutralizing Activity Against Emerging Variants First Identified in the U.K. and the Republic of South Africa. Link

Moderna, Moderna Announces Positive Initial Booster Data Against SARS-CoV-2 Variants of Concern. Link

New England Journal of Medicine, Effectiveness of the BNT162b2 Covid-19 Vaccine against the B.1.1.7 and B.1.351 Variants. Link

Jerald Sadoff, MD, et al, New England Journal of Medicine, Safety and Efficacy of Single-Dose Ad26.COV2.S Vaccine against Covid-19. Link

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