“Breakthrough” cases are not uncommon

“As of April 26, 2021, the CDC had received a total of 9,245 reports of vaccine breakthrough infections via its national COVID-19 vaccine breakthrough REDCap database, into which state health department investigators can enter and manage data from their respective jurisdictions. Of those 9,245 breakthrough cases, 55% were under the age of 60, 835 required hospitalization (9%) and 132 died (1%). With an estimated 95 million Americans having been vaccinated, the reported breakthrough rate is only 0.0097%. However, the CDC also stresses that: “It is important to note that reported vaccine breakthrough cases will represent an undercount. This surveillance system is passive and relies on voluntary reporting from state health departments which may not be complete. Also, not all real-world breakthrough cases will be identified because of lack of testing.”


FDA Comirnaty Q&A: “An analysis compared the rates of COVID-19 accrued during the current Delta surge among original clinical trial participants who completed the two-dose vaccination series early in the clinical trial, to those who completed the two-dose series later in the study because they were originally randomized to the placebo group and received the vaccine later. The analysis showed that during the study period of July and August 2021, the incidence of COVID-19 was higher among the participants who completed their vaccine series earlier, compared to participants who completed the vaccine series later. FDA determined that the rate of breakthrough COVID-19 reported during this time period translates to a modest decrease in the efficacy of the vaccine among those vaccinated earlier, equivalent to one to five percent.”


“Roughly 40% of new cases – or more than 3,000 patients – involved people who had been infected despite being vaccinated.”

Natural infection vs vaccination: Which gives more protection?

“PCR cycle threshold (Ct) values were similar between both vaccinated and unvaccinated groups at diagnosis, but viral loads decreased faster in vaccinated individuals. Early, robust boosting of anti-spike protein antibodies was observed in vaccinated patients, however, these titers were significantly lower against B.1.617.2 as compared with the wildtype vaccine strain.”

Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine-breakthrough infections: a multi-center cohort study

“Interpretation: Breakthrough Delta variant infections are associated with high viral loads, prolonged PCR positivity, and low levels of vaccine-induced neutralizing antibodies, explaining the transmission between the vaccinated people. Physical distancing measures remain critical to reduce SARS-CoV-2 Delta variant transmission.”

Study: Fully Vaccinated Healthcare Workers Carry 251 Times Viral Load, Pose Threat to Unvaccinated Patients, Co-Workers

“Of 218 individuals with B.1.617.2 infection, 84 had received a mRNA vaccine of which 71 were fully vaccinated, 130 were unvaccinated and 4 received a non-mRNA.”

Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine-breakthrough infections: a multi-center cohort study

The latest message is not that the shots will prevent you from getting COVID, but that “The bottom line: COVID-19 vaccines protect people against severe illness.” 

CDC: The Possibility of COVID-19 after Vaccination: Breakthrough Infections

FDA Comirnaty Q&A: “Based on a small number of severe cases in the data set submitted for the EUA, it was  difficult to evaluate whether the Pfizer-BioNTech COVID-19 Vaccine reduces the severity of COVID-19. ”  


“In this large population study of patients tested for SARS-CoV-2 by RT-PCR following two doses of mRNA BNT162b2 vaccine, we observe a significant increase of the risk of infection in individuals who received their last vaccine dose since at least 146 days ago, particularly among patients older than 60.”

Study: Elapsed time since BNT162b2 vaccine and risk of SARS-CoV-2 infection in a large cohort