Vaccine breakthrough infections with SARS-CoV-2: Why older adults need booster vaccinations

COVID-19 vaccinations are highly efficacious in preventing severe illness that can lead to hospitalizations and death, but incidents of vaccine breakthrough (VBT) infections persist. We examined VBT infections within a congregate setting to help guide public health practices.

This is a retrospective cohort study of VBT infections identified via polymerase chain reaction (PCR) testing between 2/1/2021-11/1/2021.

A VBT infection was defined as the detection of SARS-CoV-2 collected from a person ≥14 days after all recommended doses of a COVID-19 vaccine. VBT infections were examined in five California psychiatric inpatient hospitals with a workforce of more than 10,000 hospital staff and approximately 5500 patients.

415 VBT infections out of 14,101 fully vaccinated individuals within our system (2.9%) were identified. Days since final vaccine date ranged from 16 to 291 days. Kruskal-Wallis nonparametric test revealed a statistically significant difference in age between individuals with VBT infections versus all other vaccinated individuals [U = 6.47, p = .01]. A chi-square test of independence revealed no significant sex differences between individuals with VBT infections (58.8% male and 41.2% female) versus all other vaccinated individuals (59.6% male and 40.4% female; X2 (3, N = 14101) = 5.059, p = .167). Out of 415 VBT cases, 65.1% received the Moderna vaccine, 33.2% received Pfizer, and 1.7% received J&J; and 38.1% were asymptomatic at time of VBT infection, 24.1% were symptomatic, while 37.8% were missing symptom data.

Vaccination campaigns, including boosters and continued surveillance, are important complimentary strategies for reducing the proliferation of COVID-19 VBT cases and severity of symptoms associated with COVID-19.