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A new – albeit small — study suggests Pfizer’s coronavirus vaccine remains effective against mutated virus strains that emerged in South Africa and the U.K., and have since been detected in other parts of the world.

These strains have sparked serious concern because scientists believe they spread more easily from person to person, heightening the risk of burdening already overwhelmed health care systems and leading to additional deaths.

The study was posted ahead of peer review on bioRxiv late Thursday, meaning it has not yet undergone key scrutiny from other experts.

Pfizer paired with researchers from the University of Texas Medical Branch in Galveston for laboratory tests to see if the strains’ shared mutation, called N501Y, which alters the virus’s spike proteins, hinders the vaccine’s ability to recognize the protein.

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They used blood samples from 20 people who received the vaccine, made by Pfizer and its German partner BioNTech, during a large study of the shots. Antibodies from those vaccine recipients successfully fended off the virus in lab dishes. Despite the small sample size, Pfizer chief scientific officer Dr. Philip Dormitzer called it "a very reassuring finding that at least this mutation, which was one of the ones people are most concerned about, does not seem to be a problem" for the vaccine.

The findings begin to uphold a general consensus by other experts: The recently approved vaccines should still work against the virus. For instance, a scientist studying the variant identified in South Africa attempted to assuage concerns that existing COVID-19 vaccines will be rendered totally ineffective by the variant known as 501Y.V2.

Though mutations "may have some effect," said Richard Lessells, an infectious diseases expert with the KwaZulu-Natal Research Innovation and Sequencing Platform, which helped to first identify the variant in South Africa, "they are very unlikely to completely negate the effect of the vaccines."

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He noted that the vaccines are thought to "induce quite a broad immune response," meaning such an immune response "could target different parts of the spike protein, not just one," he told Reuters. 

The Pfizer official, Dormitzer, said this was only the beginning "of ongoing monitoring of virus changes to see if any of them might impact on vaccine coverage."

Further, there is still concern that the coronavirus variant initially detected in South Africa can reduce neutralizing power from antibody drugs, including convalescent plasma. Dr. Scott Gottlieb, the former commissioner of the FDA, told CNBC’s Shepard Smith Tuesday that the strain appears to "obviate" some countermeasures.

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"The South Africa variant is very concerning right now because it does appear that may it obviate some of our medical countermeasures, particularly the antibody drugs," Gottlieb said, pointing to evidence from Bloom Lab.

Also, it is still unclear whether the recently approved coronavirus vaccines can prevent virus spread, in addition to halting disease. 

The news of the study comes as a number of states announced their first known cases of the U.K. coronavirus variant on Thursday, including Pennsylvania, Texas and Connecticut. These states join others that have previously detected the strain, like California, Colorado, Florida, Georgia and New York.

The Centers for Disease Control and Prevention has already identified over 50 cases of the U.K. variant strain across the U.S. 

The other worrying strain first detected in South Africa has yet to be reported in the U.S., though it has cropped up in other countries, like Austria, Switzerland, Japan, France, Zambia and the U.K., per a report by CNBC. 

The Associated Press and Fox News' Madeline Farber contributed to this report.