A novel coronavirus, SARS-CoV-2 (formerly known as the 2019 novel coronavirus \[2019-nCoV\]) was identified as the agent that caused an outbreak of pneumonia (termed COVID-19) in Wuhan, China in December 2019. The virus quickly spread to other countries and on March 11, 2020, the World Health Organization (WHO) declared COVID-19 a pandemic. By March 2021, many nations and organizations embarked on finding a cure or vaccine for this devastating viral infection. The Pfizer COVID-19 mRNA vaccine was the first to obtain emergency use authorization (EUA) from the Food \& Drug Administration (FDA) on December 11, 2020, followed by the Moderna COVID-19 mRNA vaccine on December 18, 2020, and the Janssen COVID-19 viral vector vaccine on February 27, 2021. The mRNA vaccines and the viral vector vaccine are designed based on the spike protein of SARS-COV-2. These vaccines had been administered to millions of Americans prior to July 2021.

Similar to other infections that are preventable with vaccination, COVID-19 vaccination is not a SARS-CoV-2 infection panacea. However, in fully vaccinated people the risk of SARS-CoV-2 infection, hospitalization, severe illness, and death from COVID-19 is relatively less. Viruses may escape the host immune defense through mutations that create new variants of the primary virus. Some variants emerge and disappear while others persist and may have properties that may be different from the primary virus. By late 2020, a new variant, the delta variant, was identified in Maharashtra, India. This variant is highly transmissible and causes infections even in fully vaccinated people, it is less sensitive to neutralizing antibodies from recovered subjects and less sensitive to vaccine-induced antibodies, and there is evidence that it causes more severe infections. While the world was trying to contain and control the spread of the delta variant, the WHO reported a new variant of COVID-19, omicron. It was detected in late November 2021 in specimens collected in Botswana and South Africa. New variants of SARS-CoV-2 are expected to continue to emerge and the world continues to seek means of controlling the pandemic.

COVID-19 vaccination data from the Centers for Disease Control and Prevention (CDC) showed that the population ratios who have received a full series of COVID-19 vaccination from Pfizer, Moderna, or Janssen as of February 2, 2022 is 17.46/11.25/1. Furthermore, more of those who received the Janssen COVID-19 viral vector vaccine have preferred and received an mRNA vaccine booster. Unfortunately, the CDC data lacks the booster dose data for Texas residents.

The FDA in collaboration with the CDC makes decision on when a booster is recommended. This decision is based on many factors including the level of antibodies and memory cells post-COVID-19 vaccination and infection. There is much evidence that decreasing the COVID-19 spike antibodies titer and memory cells may increase the likelihood of a breakthrough COVID-19 infection. Unfortunately, there isn't a prior report or study comparing the incidence of COVID-19 infection among people fully vaccinated with any of the approved COVID-19 vaccines. This study seeks to find a relationship between the last dose of a COVID-19 vaccine in a fully vaccinated person and a COVID-19 breakthrough infection. The study will also find a correlation between the duration from a booster dose to the diagnosis of a breakthrough COVID-19 infection.