Booster COVID-19 vacc cuts breakthrough infection risk, particularly in individuals with no immune dysfunction

Receipt of a booster dose of the COVID-19 vaccine reduces the risk of breakthrough COVID-19 infections* compared to full vaccination only, particularly among individuals without immunosuppressed/compromised conditions (ISC), according to a US study presented at CROI 2022.

The study was conducted using patient-level data from the US National COVID Cohort Collaborative (N3C). Individuals who had received booster doses of the COVID-19 vaccine were propensity-score matched** with those who completed full vaccination (two doses of an mRNA vaccine or one dose of the Janssen vaccine) between December 10 and 17, 2021. A total of 784,555 individuals had received full vaccination (median age 50 years, 57 percent female, 55 percent White). Seventy-one and 25 percent had received the BNT162b2 and Moderna vaccines, respectively.

Among the 174,042 individuals who had received a booster, median time to booster dose was 7.4 months since last dose. Compared with non-recipients, booster recipients were older (median age 57 vs 49 years), more likely to be White (63 percent vs 53 percent) or Asian American or Pacific Islander (5.8 percent vs 4.6 percent), and have ≥3 comorbidities (16 percent vs 12 percent).

Twenty percent of participants had ISC, which in this study was defined as HIV infection, solid organ or bone marrow transplant, autoimmune diseases, or cancer.

A total of 48,893 breakthrough infections were documented up to January 14, 2022, with weekly breakthrough infections increasing after delta and omicron became the dominant strains in the US.

Among individuals without ISC, the efficacy of the booster was 70.5 percent for those who received the booster ≤5 months since completion of full vaccination (hazard ratio [HR], 0.33, 95 percent confidence interval [CI], 0.22–0.52) and was greatest for those who received it 7 months post-full vaccination (77.4 percent efficacy; HR, 0.23, 95 percent CI, 0.19–0.27; p<0.001 for both). [CROI 2022, abstract 48]

Individuals with ISC had a greater incidence of breakthrough infections regardless of booster status, noted study author Dr Jing Sun from the Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, US.

The reduced risk of breakthrough COVID-19 infection was still greater in booster recipients than non-recipients among individuals with ISC, though vaccine efficacy was slighter lower than that in patients without ISC. Booster efficacy was 40.5 percent for receipt at 6 months after full vaccination (HR, 0.60, 95 percent CI, 0.47–0.75) and 60.2 and 60.1 percent for receipt at 7 and 8 months after full vaccination (HRs, 0.39 and 0.38, respectively; p<0.001 for all).

In the non-ISC group, booster efficacy was 70.5, 73.6, 77.4, 62.5, and 52.1 percent for those who received it at ≤5, 6, 7, 8, and 9 months after full vaccination, respectively. In the ISC group, booster vaccine efficacy was 40.5, 60.2, 60.1, and 39.5 percent at 6, 7, 8, and 9 months since full vaccination.

In individuals without ISC, receipt of a booster reduced their risk of hospitalization (odds ratio [OR], 0.13), invasive ventilation (OR, 0.09), and death (OR, 0.13; p<0.001 for all) compared with those who did not receive a booster***. Similar benefits were noted with a booster among individuals with ISC, but to a lesser degree (ORs, 0.21, 0.25, and 0.17, respectively; p<0.001 for all).

“A booster dose of COVID-19 vaccine has high effectiveness in reducing breakthrough infection risk among fully vaccinated individuals,” presented Sun.

“Although the effectiveness against breakthrough infection is lower among patients with immune dysfunction, [the booster] still reduced the risk of breakthrough infection significantly after 6 months of full vaccination in this high-risk cohort,” she added.

The booster was also highly effective against severe COVID-19 outcomes among individuals regardless of their ISC status, she said.