key: cord-1008915-0glijsgq
authors: Butt, Adeel A.; Khan, Tasnim; Yan, Peng; Shaikh, Obaid S.; Omer, Saad B.; Mayr, Florian
title: Rate and Risk Factors for Breakthrough SARS-CoV-2 infection After Vaccination
date: 2021-05-28
journal: J Infect
DOI: 10.1016/j.jinf.2021.05.021
sha: 44f1b58aa893da840822070edc5075f8157d3631
doc_id: 1008915
cord_uid: 0glijsgq

nan

We identified all Veterans who received two doses of the Pfizer-BNT-162b2 or Moderna-mRNA-1273 vaccine between December 15, 2020 and March 31, 2021 from the national VA COVID-19 Shared Data Resource. We excluded those with a positive SARS-CoV-2 PCR on a nasopharyngeal swab within 14 days of receiving the first vaccine dose. From the remaining persons, we retained those who had at least one SARS-CoV-2 PCR test performed on a nasopharyngeal swab >7 days after the second dose vaccine dose. Cases were those with confirmed SARS-CoV-2 infection and controls were those who remained uninfected with at least one confirmed negative test for SARS-CoV-2 >7 days after their second vaccine dose.

Among a total of 258,716 fully vaccinated persons, we identified 410 persons with breakthrough infection and 14,465 controls. Median age (IQR) was 73 (68,78) years for the infected group and 72 (66,76) for the uninfected group (P=0.0002). There were more Whites in the infected group (76.6% vs. 69.1%; P=0.01)) compared with the uninfected group. Prevalence of comorbidities was similar in the two groups except anemia, which was more common in the infected group.

Overall infection rate >7 days after the second vaccine dose was 0.66 (95% CI 0.60,0.72) per 1,000 person-days of follow up. ( 

To our knowledge, this is the first study to describe the rate and risk factors for SARS-CoV-2 breakthrough infection in persons who have been fully vaccinated. We found a low rate of infection among those who were fully vaccinated and age, race and anemia to be associated with confirmed infection.

We found relatively few factors associated with infection after vaccination. Increasing age increased the risk, as did presence of anemia at baseline. Increasing age is a well-recognized risk factor for SARS-CoV-2 infection and is also associated with more severe disease and poorer clinical outcomes. Therefore, it is not surprising that it would also be associated with infection after vaccination. Multiple comorbid conditions are also associated with a higher risk and increased severity of infection. The reason for the association of anemia with infection after vaccination while no association was demonstrable other comorbidities is unclear. While we used the standard World Health Organization definition of anemia (i.e. hemoglobin <13g/dL for men and <12 g/dL for women), this may be too permissive. We did not assess the association of the degree of anemia with the risk of infection. Whether this association is limited to more severe anemia, which may worsen oxygenation, is not known.

Surprisingly, Black race was associated with a lower risk of infection. The reason for this is entirely unclear. It is possible that the Blacks who were vaccinated were younger and healthier and at a lower risk of infection at the outset. It is equally possible that they were older and less healthy and due to those reasons they were less mobile and therefore less likely to be exposed to persons with confirmed infection. Further studies are warranted to confirm this finding and to understand the reasons for this finding.

Our study has several strengths. We studied a national population with diverse geographical and demographic characteristics who receive care within a single integrated healthcare network.

Vaccines, SARS-CoV-2 testing, and clinical care are provided free or cost or with minimal expense to qualified Veterans. The VA created a national database of SARS-CoV-2 infected Veterans using validated definitions and algorithms which is regularly updated and provides a rich resource for clinical and observational studies. Despite these strengths, several limitations need to be noted. Veterans are predominantly male. We did not assess the actual exposure to confirmed cases. We also did not assess the clinical severity of disease and outcomes in our study population, which will be the subject of a subsequent study.

In conclusion, the rate of infection among persons who have been fully vaccinated is low but not insignificant. Increasing age and presence of anemia increase the risk, while Black race is associated with a lower risk. An awareness campaign, particularly targeted to those at risk is needed to mitigate the risk. 

Effectiveness of BNT162b2 vaccine against the B.1.1.7 variant of SARS-CoV-2 among healthcare workers in

BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Mass Vaccination Setting

SARS-CoV-2 Infection after Vaccination in Health Care Workers in California

Early Evidence of the Effect of SARS-CoV-2 Vaccine at One Medical Center

Antibody Responses in Seropositive Persons after a Single Dose of SARS-CoV-2 mRNA Vaccine

Effectiveness of the BNT162b2 Covid-19 Vaccine against the B.1.1.7 and B.1.351 Variants