[1] Breakthrough infections have been identified in individuals immunized against a variety of diseases including mumps, varicella (Chickenpox), influenza, and COVID-19.
However, if herd immunity exists, it typically prevents individuals who are ineffectively vaccinated from contracting the disease.
[5] These individuals with mild varicella have low fevers, fewer than 50 lesions on their skin, and a maculopapular rash.
Evolution of the virus (antigenic drift) is thought to explain the majority of breakthrough cases.
[13] Other theories suggest that memory T lymphocytes play a role in the development of breakthrough infections.
Breakthrough infections may also be caused by delayed vaccination, immunosuppression, and maternal viral load.
[14] In April 2021, scientists reported that in a cohort of 417 vaccinated persons, two women had breakthrough infections as of publication and identified their variants' viral mutations.
[17][18] In the same month, the CDC reported that in the United States, there were 5,814 COVID-19 breakthrough infections and 74 deaths among the more than 75 million people fully vaccinated for the COVID-19 virus.
[19][20][21][22][23][24] In July 2021, scientists reported that in an outbreak of the SARS-CoV-2 Delta variant, associated with large public gatherings, 74% of infections occurred in fully vaccinated people.
[29] The presence of maternal antibodies in infants limits the efficacy of inactivated, attenuated and subunit vaccines.
The level of memory B-cells is not adequate to ensure an infant's lifelong resistance to the pathogen.
[32] When a person is vaccinated, their immune system develops antibodies that recognize specific segments (epitopes) viruses or viral-induced proteins.
Over time, however, viruses accumulate genetic mutations which can impact the 3D structure of viral proteins.
[35] Failure to account for these factors can lead to patients receiving an incorrect amount of vaccination.