A California study titled “Predominance of antibody-resistant SARS-CoV-2 variants in vaccine breakthrough cases from the San Francisco Bay Area, California” find vaccinated individuals are more susceptible to COVID variants than those who are unvaccinated.

Additionally, an increase in the frequency of more antibody-resistant strains in the population correlates with the increase in the frequency of vaccination in the population.

The study’s introduction explains:

Vaccines targeting the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been highly effective in preventing symptomatic illness and in reducing hospitalizations and deaths from coronavirus disease 2019 (COVID-19)1–8.

Prior studies have also suggested that vaccination may reduce viral loads in persons with breakthrough SARS-CoV-2 infection who have received at least one dose7,9, thus potentially decreasing infectiousness and mitigating transmission.

The introduction then goes into the missing piece:

However, most of these studies were done prior to the emergence of “antibody-resistant” SARS-CoV-2 variants of concern / variants of interest (VOCs/VOIs) carrying key mutations that have been shown to decrease antibody (Ab) neutralization (L452R/Q, E484K/Q, and/or F490S), including the beta (B.1.351), gamma (P.1), delta (B.1.617.2), epsilon (B.1.427/B.1.429), and lambda (C.37)10, but not alpha (B.1.1.7) variants11–13. 

Breakthrough infections have been reported in a small proportion of vaccine recipients3,14–17, yet little is known regarding the relative capacity of different variants to escape vaccine-induced immunity and facilitate ongoing spread within highly vaccinated communities.

The study provides multiple charts comparing variant susceptibility in both fully vaccinated, partially vaccinated and unvaccinated individuals, as well as in depth details on the study methods.

The study summarizes:

 In unvaccinated cases, most viruses consisted of non-resistant variants (61% and 57% based on community and UCSF testing, respectively) (Figure 2A, right), in contrast to vaccinated cases, for which the proportions of non-resistant variants dropped to 34% and 20%, respectively (Figure 2A, left). Alpha was the only non-resistant variant associated with breakthrough infection in vaccinated cases.

 Overall, fully vaccinated cases were significantly more likely than unvaccinated cases to be infected by resistant variants (77.6% versus 47.7%, p=1.96e-08) (Figure 2B, top and Table 1), but not by variants associated with increased infectivity (84.7% versus 76.8%, p = 0.092) (Figure 2B, bottom and Table 1).