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Experts: COVID Variants Are Not Causing More Infections In Vaccinated People

A digital illustration of a COVID virus particle in a circle with data points surrounding it.

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Key Takeaways

  • According to data from the Centers for Disease Control and Prevention (CDC), COVID-19 variants of concern are not causing a disproportionate number of infections in vaccinated people in the United States.
  • Breakthrough cases are rare, mostly mild, and occurring at an anticipated rate.
  • Public health experts are worried that unvaccinated people will generate additional and potentially more concerning variants that will threaten global health.

According to a new report from the Centers for Disease Control and Prevention (CDC), COVID-19 variants of concern are not currently causing a disproportionate number of SARS-CoV-2 infections in vaccinated people in the United States.

Public health experts say that "breakthrough" COVID infections in people who are fully vaccinated are rare, generally mild, and occurring at an expected rate.

What Is a 'Breakthrough' Case of COVID?

When a person who is vaccinated against COVID-19 tests positive for SARS-CoV-2, they have what’s called a breakthrough infection. The CDC recently released a report on breakthrough infections, stating that they “occur in only a small fraction of all vaccinated persons and account for a small percentage of all COVID-19 cases.”

The CDC had genome sequencing data on 555 (about 5%) of the breakthrough cases reported. Over half (64%) of those cases were identified as a "variant of concern"—with the largest proportion identified as the U.K. strain B.1.1.7, which is now the dominant variant in many parts of the country.

The CDC concluded that “the proportion of reported vaccine breakthrough infections attributed to variants of concern has also been similar to the proportion of these variants circulating throughout the United States.”  

“The story about variants and breakthrough cases at the moment, is the variants are not disproportionately causing breakthroughs," William Schaffner, MD, medical director of the National Foundation for Infectious Diseases (NFID) and professor of medicine in the division of infectious diseases at the Vanderbilt University School of Medicine, tells Verywell.

In general, Schaffner says that breakthrough cases are anticipated and most are mild. However, there are some severe cases.

“Remember, we said vaccines, at their best, were 95% effective,” says Schaffner. “We didn’t say 100%. And of course, we’re now vaccinating many frail, sometimes immunocompromised people. And we see a fair number of those in breakthrough cases. In other words, these are people who did not have an optimal 95% protection response to the vaccine.” 

Approximately 101 million people in the U.S. were fully vaccinated against COVID-19 by the end of April 2021. In that time, the CDC says that 10,262 breakthrough cases were reported from 46 states and territories.

After initially surveilling all reported breakthrough cases, the CDC is no longer investigating mild infections in vaccinated individuals.

Concerns About the Unvaccinated

While they are not concerned about variants among people who have been fully vaccinated, public health experts are worried about vaccine-hesitant populations and people who have not yet had access to COVID vaccines yet.

Unvaccinated people could easily contract a more infectious variant or even generate a completely new and more harmful variant that vaccines might not protect against.

Schaffner says that if unvaccinated people get infected, the virus will multiply. 

“If it multiplies, it mutates," says Schaffner. "And it could mutate into a dangerous variant in any individual. So they are potential variant factories—everybody who is unvaccinated.”

COVID Variants in the U.S.

Viral variants (also called mutations) are a normal and constant viral process. Mutations are not usually a cause for concern beyond the implications of the original virus. However, some genetic changes raise red flags. 

Classifying Variants

According to the CDC, the U.S. has a variant labeling system that classifies a viral variant as being a variant of interest, a variant of concern, or a variant of high consequence.

Why Names Matter

Variants have a lineage name consisting of letters and numbers, and often a geographic name that is used for ease of discussion. Experts are expressing the importance of not using the strain's regional name with the intent to stigmatize a population.

Gary Schoolnik, MD, an infectious diseases expert and a professor of medicine at Stanford and the chief medical officer of Visby Medical, tells Verywell that “when a variant arises, as a component of the natural evolution of the virus, it will arise in a single geographic area, and we can anticipate it will then spread globally.”

K.C. Rondello, MD, clinical associate professor and university epidemiologist at Adelphi University, tells Verywell that mutations are not necessarily a problem. Most mutations "don't have any impact on how effectively a virus spreads, the severity of the symptoms it causes, how well treatments and vaccines developed for it work, or any other change from the wild-type (or base) strain."

However, that's not always the case. Rondello says that “a minority of genetic changes result in the evolution of variants of concern.”

Variants of Interest 

A variant of interest has specific genetic markers that are predicted to affect its transmission, how it is tested for, the efficacy of vaccines against it, and treatment response. Additionally, a variant of interest shows evidence of increased cases or outbreak clusters but has a limited prevalence in the U.S. or in other countries.

Currently, the CDC has identified several COVID variants of interest in the U.S.:

  • B.1.525 (UK/Nigeria strain)
  • B.1.526 (New York strain)
  • B.1.526.1 (New York strain)
  • B.1.617 (India strain)
  • B.1.617.1 (India strain)
  • B.1.617.2 (India strain)
  • B.1.617.3 (India strain)
  • P.2 (Brazil strain)

“Internationally, high on the radar of epidemiologists is the variant first identified in India late last year, B.1.617,” says Rondello. “The variant has now spread to dozens of other countries, including the United States and the United Kingdom. Preliminary data seems to indicate that vaccines are largely protective against the B.1.617 variant causing severe disease, hospitalization, and death.”

Variants of Concern

A variant of concern shows evidence of an impact on testing, treatments, and vaccine efficacy, as well as evidence of increased transmissibility, and increased COVID-19 illness severity.

The CDC has currently identified several variants of concern in the U.S.:

Common Variants in the U.S. Right Now

Schaffner says that the most common variant in the U.S. is B.1.1.7, also known as the U.K. strain. It’s highly contagious—more so than the original SARS-CoV-2 strain—and it has become the dominant strain in many parts of the country. 

William Schaffner, MD

The story about variants and breakthrough cases at the moment, is the variants are not disproportionately causing breakthroughs.

— William Schaffner, MD

“That has everything to do with the fact that from a competitive point of view, since it’s so contagious, it’s beating the parent, if you will,” says Schaffner. “Fortunately, this variant is still well covered by our vaccines. And so, the vaccines we are using today will protect very securely against this variant, as will masks and social distancing.”

The California strains, the South Africa strain, and the Brazil strain are also present in the U.S., but in smaller numbers. Schaffner says that at the moment, these strains are not gaining much traction in the states "because their contagiousness is less than this British variant, and the British variant is just outrunning them.”

Vaccinated individuals are largely protected from variants of concern. “Except for the South African variant, once again, we’re in pretty good shape with these vaccines,” says Schaffner, “because they do cover the Brazilian variant and the California variants.”

Variants of High Consequence

A variant of high consequence shows the same red-flag evidence as a variant of concern but also demonstrates testing failures, a significant reduction in vaccine efficacy, a high number of cases in vaccinated people, and more severe cases that are harder to treat with existing therapeutics.

Currently, the CDC has not identified any variants of high consequence in the U.S.

Testing for Variants 

Schaffner says that infectious disease experts, in conjunction with the CDC and the World Health Organization (WHO), are monitoring variants on an ongoing basis through what’s called genome sequencing.

According to Schaffner, patients who are being selectively tested for variants include:

Public health experts also take a random sampling of cases to track which strains are circulating, though Schaffner says that the process currently varies from state to state. 

Why Vaccines Are Important

Public health experts say that to fight the variants, including future mutations that could be classified as variants of high consequence, vaccinating as many people as possible is vital.

“Once a substantial portion of the population is vaccinated, then neither the original Wuhan variant nor the Indian variant or any other variant that’s still covered by the vaccine will be able to spread as readily," says Schoolnik. "So the best defense against variants is clearly vaccination.”

William Schaffner, MD

The best defense against variants is clearly vaccination.

— William Schaffner, MD

According to Schoolnik, SARS-CoV-2 is one of the most quickly replicating viruses, generating billions of copies in a single individual. Amongst those billions of viruses will be mutants that spontaneously arise because errors are made each time the virus gets copied.

“Some of those variants that are generated in a particular individual will have an advantage over all of the other variants and the original virus that infected that person,” says Schoolnik. “And the biggest advantage it will have is being more readily transmissible. It’s just basic Darwinian evolution at work on a very short timescale.”

Protecting Everyone—But Especially the Most Vulnerable

The CDC recently logged the milestone that more than 50% of the adult population in the U.S. is now vaccinated—but Schaffner points out that almost half are not.

As an infectious disease expert, Schaffner says that this troubles him—not only for the safety of those individuals and for combating the potential development of new possibly more dangerous variants, but also for protecting vulnerable populations.

“There are many people among us who have illnesses or take medications that suppress their immune systems,” says Schaffner. “Those people can’t respond optimally to the vaccine because their immune system is suppressed. How do we protect them? Well, we vaccinate them and try to get some partial protection. But the best way we can protect our frail brothers and sisters is by the rest of us getting vaccinated.”

Global Vaccination Efforts

Widespread global vaccination—not just domestic—is ultimately needed to control and combat COVID variants.

Schaffner says that we have to think about controlling the pandemic "beyond our own borders" because "if there’s another variant in another country, or wherever, a person infected with that variant can get on a plane, come here, and of course it can start spreading here. The variants don’t need passports.” 

Gary Schoolnik, MD

Until we vaccinate the world, nobody is safe, even in countries where the vaccine level may be at 60 to 70%.

— Gary Schoolnik, MD

Schoolnik agrees with Schaffner and adds that "it is possible, and even probable, that at some point, a variant will be generated in an unvaccinated person here or abroad that will not only be more transmissible but will be unblocked by the vaccine and may even be more virulent."

According to Schoolnik, the bottom line is that “until we vaccinate the world, nobody is safe, even in countries where the vaccine level may be at 60 to 70%.”

Vaccine Equity

Much to that end, global vaccine access is also about equity. In a press statement, Tom Kenyon, MD, MPH, chief health officer at Project HOPE and former director of global health at the CDC, said “one of the greatest health inequities of all time is currently underway due to the shortages in COVID-19 vaccine supply, vaccine hoarding by wealthier nations, and their failure to use the WHO’s COVAX facility for more equitable vaccine distribution."

Kenyon added that “we must prioritize access and increasing supply to achieve global vaccine equity as soon as possible—so those who want the lifesaving benefits of vaccines get the protection they rightfully deserve.” 

Will Variants Mean Booster Shots?

The duration of protection from current COVID-19 vaccines is still unknown. “So far, the protection afforded by the vaccines in people who are completely vaccinated is very sturdy at six months,” says Schaffner. “And going on, it appears not to be diminishing. So we’ll keep following that.”

If a new variant were to appear that could evade vaccine protection, that would affect the need for a booster. That hasn’t happened yet, but Schaffner says that public health experts are watching the situation carefully. He says that it's also “why we are reluctant to speculate about whether a booster will be necessary or at what interval. Stay tuned.”

What This Means For You

If you’ve received a COVID-19 vaccine, it should provide protection from variants currently circulating in the U.S. If you have not received a COVID-19 vaccine, you could be at risk for contracting a variant and infecting someone, or even generating a new worrisome mutation that could worsen the pandemic.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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  1. Centers for Disease Control and Prevention (CDC). COVID-19 vaccine breakthrough infections reported to CDC — United States, January 1–April 30, 2021MMWR Morb Mortal Wkly Rep. 2021;70:792–793. doi:10.15585/mmwr.mm7021e3

  2. Centers for Disease Control and Prevention (CDC). SARS-CoV-2 variant classifications and definitions. Updated May 25, 2021.