Study shows SARS-CoV-2 breakthrough infections fewer among fully vaccinated

Vaccination efforts against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pathogen behind the coronavirus disease (COVID-19) pandemic, commenced in many countries in December 2020. Over 3 billion vaccine doses have since been administered worldwide.

A team of researchers at Indiana University reports genomic evidence of breakthrough infections in fully vaccinated individuals. The study, posted to the pre-print server medRxiv*, suggests that fully vaccinated individuals, including those with asymptomatic infections, are less likely to serve as a source of infection for others.

Vaccinating against SARS-CoV-2

Some SARS-CoV-2 infections are asymptomatic or cause mild symptoms, but other individuals are severely affected. Vulnerable individuals include the elderly, those with weakened immune systems, and those with underlying health conditions.

To date, the infection has caused over 181 million cases and 3.93 million deaths worldwide. With the development and rapid rollout of COVID-19 vaccines, the positivity rate across the United States has decreased. Reinfections are reported to be from 2 to 12 percent.

Some people have experienced breakthrough infections, wherein SARS-CoV-2 RNA or antigen is detected in respiratory specimens collected from a person more than 14 days after receiving two doses of a COVID-19 vaccine.

In the U.S., a person is considered fully vaccinated two weeks after a two-dose vaccine from Pfizer-BioNTech mRNA COVID-19 vaccine or Moderna vaccine or two weeks after a dose of the adenoviral vectored vaccine from Johnson & Johnson/Janssen.

A thorough understanding of breakthrough infections is essential for public health officials, scientists, and healthcare professionals to develop booster vaccines. Moreover, it will help monitor reinfections and determine if current vaccines are effective at preventing infection. This is essential as new variants are rapidly emerging, threatening the efficacy of the current COVID-19 vaccines.

The study

In the current study, the team aimed to survey nucleic acid testing and analyze viral whole-genome sequences to detect breakthrough infections. They collected anterior swabs from the students and employees on the Indiana University campus.

These samples were examined for a nucleic amplification test (NAAT) to detect SARS-CoV-2. In addition, positive samples were sequenced to determine variants tied to the infections. Included in the testing and sequencing protocol were those who received complete vaccination against COVID-19.

The study findings showed that between February 10, 2021, and May 10, 2021, the team conducted 2,551 nucleic acid amplification tests from samples from fully vaccinated individuals. Of these, 14 showed breakthrough infections.

To compare, the team tested 65,877 samples from unvaccinated or partially vaccinated individuals during the same period. They detected 1,482 positive people by NAAT. Of the breakthrough infections, six received the Pfizer vaccine, five received the Moderna vaccine, and three had J&J vaccine jabs.

Interestingly, some individuals had high viral loads, while most breakthrough infections were tied to variants of concern B.1.1.7 and P.1.

While about 45 percent of vaccine breakthrough infections have been reported in people older than 60, these data demonstrated that these infections also occur in young adults, particularly college-aged individuals. In addition, a majority of these infections were also seen in asymptomatic individuals.

According to the team, fully vaccinated individuals are less likely to become a source of infection for others. However, further investigation is still needed. In addition, the number of people who tested positive was lower in the vaccinated group than in the unvaccinated or partially vaccinated groups.

“Fewer detected breakthrough infections in the full-vaccinated group reinforces the need to get vaccinated to decrease the spread of SARS-CoV-2 infection. Our observations provide support for the need for sustained efforts to diagnose asymptomatic infections and characterization of variants,” the researchers concluded in the study.

Determining breakthrough infections and if they can transmit the virus is crucial in the fight against the pandemic. The proper and timely isolation of positive individuals can help prevent further viral spread. There have been over 33.65 million cases in the United States, with more than 604,000 deaths tied to COVID-19.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Angela Betsaida B. Laguipo

Written by

Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She is currently completing her Master's Degree where she specialized in Maternal and Child Nursing and worked as a clinical instructor and educator in the School of Nursing at the University of Baguio.


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