New Study Finds COVID-19 Booster Shot Reduces Breakthrough Infection

COVID-19 booster shot reduces the likelihood of a breakthrough infection, especially in people who don't have any immunological problems.

New Study Finds COVID-19 Booster Shot Reduces Breakthrough Infection
Image: COVID-19 Booster Shot | InStyleHealth


According to a US study presented at CROI 2022, receiving a booster dose of the COVID-19 vaccine decreases the probability of breakthrough COVID-19 infections  compared to full immunization alone, especially among patients without immunosuppressed/compromised conditions (ISC).

The research was based on patient-level data from the National COVID Cohort Collaborative in the United States (N3C). Between December 10 and 17, 2021, those who got COVID-19 booster doses were propensity-score matched with those who completed full vaccination (two doses of an mRNA vaccine or one dose of the Janssen vaccine). A total of 784,555 people had been fully vaccinated (median age 50 years, 57 percent female, 55 percent White). The BNT162b2 and Moderna vaccines were given to 71% and 25% of the people, respectively.

The median period from last dosage to booster dose was 7.4 months among the 174,042 people who had received a booster. 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% vs 4.6%), and had three comorbidities than non-recipients (16 percent vs 12 percent).

ISC was characterized in this study as HIV infection, solid organ or bone marrow transplant, autoimmune disorders, or cancer in 20% of the individuals.

Up until January 14, 2022, a total of 48,893 breakthrough infections were recorded, with weekly breakthrough infections increasing once delta and omicron became the leading strains in the United States.

The booster's efficacy was 70.5 percent for those who received it 5 months after finishing full vaccination (hazard ratio [HR], 0.33, 95 percent confidence interval [CI], 0.22–0.52), and was highest for those who received it 7 months after finishing full vaccination (77.4 percent efficacy; HR, 0.23, 95 percent confidence interval [CI], 0.19–0.27; p0.001 for both). [Abstract 48, CROI 2022]

Regardless of booster status, people with ISC had a higher rate of breakthrough infections, according to research author Dr. Jing Sun of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland.

Among people with ISC, the lowered risk of breakthrough COVID-19 infection was still higher in booster recipients than non-recipients, despite vaccine efficacy being slightly lower than in patients without ISC. Booster efficacy was 40.5 percent when given 6 months after full vaccination (HR: 0.60, 95 percent CI: 0.47–0.75), and 60.2 and 60.1 percent when given 7 and 8 months after full immunization (HRs: 0.39 and 0.38, respectively; p0.001 for all).

Booster efficacy in the non-ISC group was 70.5, 73.6, 77.4, 62.5, and 52.1 percent, respectively, for those who got it 5, 6, 7, 8, and 9 months after complete immunization. At 6, 7, 8, and 9 months after full vaccination, booster vaccine efficacy in the ISC group was 40.5, 60.2, 60.1, and 39.5 percent, respectively.

When compared to those who did not receive a booster, those who did have a booster had a lower chance of hospitalization (OR, 0.13), invasive ventilation (OR, 0.09), and mortality (OR, 0.13; p0.001 for all)***. Individuals with ISC experienced similar improvements with a booster, albeit to a lower extent (ORs, 0.21, 0.25, and 0.17, respectively; p0.001 for all).

"Among fully vaccinated persons, a booster dose of COVID-19 vaccine had high efficiency in reducing breakthrough infection risk," Sun said.

"Although the effectiveness against breakthrough infection is decreased in individuals with immunological dysfunction, [the booster] nevertheless significantly reduced the risk of breakthrough infection in this high-risk population after 6 months of full immunization," she continued.

She added that the booster was also highly effective against severe COVID-19 results in people of all ISC statuses.
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