COVID booster significantly improves protection against Omicron hospitalization: JAMA

CHICAGO: A US case-control research published in JAMA Network shows that, three doses of an mRNA COVID-19 vaccination were associated with a 59% lower risk of hospitalization than two doses, even though protection diminished over time.

Less is known about the amount of immunity conferred by a booster shot and how long that coverage lasts among people who have already received the entire primary series of an mRNA vaccine.

According to the authors, "mRNA boosters were linked with lower risks of hospitalization in a large US population compared with the mRNA vaccination primary series alone, with the magnitude of the association attenuating with more time since the booster dose."

They mentioned research showing a 55% to 99% decreased risk of COVID-19 among those who received a booster dose compared to their uninfected counterparts. "This study was able to quantify the extra benefit of a booster dose to the primary series by matching cases with controls based on the date of second mRNA dose," they stated.

The probabilities of COVID-19 hospitalization were compared by the researchers between vaccination with the primary mRNA vaccination series alone and vaccination with the COVID-19 mRNA booster immunization.

Researchers from the University of Chicago calculated the likelihood that adults who were hospitalized in the Providence Health & Services network in one of six Western states from October 1, 2021, to July 26, 2022, would experience a COVID-related hospitalization after receiving only the primary vaccination series (two doses) or a third (booster) dose of an mRNA vaccine. 81% of instances during the research period had the Omicron variation as the cause. Every one of the 3,062 COVID-19 patients was matched in a ratio 1:4 with 12,248 control patients who were admitted to the hospital for non-COVID indications within three days of the case-patient and who lived in the same area. The control patients also received a second dose of the vaccine (Pfizer/BioNTech or Moderna) within seven days of the case-patient. A total of 12 248 matched controls with a mean age of 67.1 [SD, 18.2] years, 46.7% of whom were males, and 3062 cases with a mean age of 70.8 [SD, 15.4] years, 52.6% of whom were men, and 34.7% of whom were boosted, were included. Age of 70 years or more, male sex, cognitive disease, chronic obstructive pulmonary disease, diabetes, immunodeficiency, obesity, rheumatologic disease, transplant, and BNT162b2 (Pfizer-BioNTech) vaccine were all factors linked to an elevated risk of hospitalization for COVID-19.

Key conclusive points of the study:

• According to the multivariable analysis, booster vaccination was linked to a lower risk of hospitalization for COVID-19 (34.7 percent of cases versus 49.3 percent of matched controls; adjusted OR, 0.41 [95% CI, 0.37-0.46]).
• Depending on when the booster was administered, different hospitalization probabilities applied: less than 50 days (adjusted OR, 0.24 [95% CI, 0.18-0.30]), 50 to 100 days (adjusted OR, 0.24 [95% CI, 0.20-0.29]), 101 to 150 days (adjusted OR, 0.47 [95% CI, 0.38-0.58]), and longer than 150 days (adjusted OR, 0.72 [95% CI, 0.61-0.84]).

This study "shows us that there is a real utility in obtaining a booster shot even if you are completely immunized, "stated the authors. "People who had boosters were far less likely to experience severe Covid for 4-5 months after the booster shot" than those who only received their initial vaccines."

The total risk of hospitalization among patients who have had vaccinations is low, the authors concluded, even if the increased protection provided by a third dose gradually diminishes with time.

REFERENCE

Ridgway JP, Tideman S, French T, et al. Odds of Hospitalization for COVID-19 After 3 vs 2 Doses of mRNA COVID-19 Vaccine by Time Since Booster Dose. JAMA. Published online September 23, 2022. doi:10.1001/jama.2022.17811