In a recent study published in the Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report, researchers compared the effectiveness of double booster severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) messenger ribonucleic acid (mRNA) vaccinations and single booster vaccinations among nursing home residents (NHR) in the United States (US).
The continual emergence of novel SARS-CoV-2 variants has threatened vaccine efficacy across the globe. Studies have reported SARS-CoV-2 vaccine efficacy in preventing severe coronavirus disease 2019 (COVID-19) among NHMs; however, data on SARS-CoV-2 booster dose vaccine effectiveness (VE) among NHRs are limited.
About the study
In the present study, researchers evaluated the second COVID-19 mRNA booster VE estimates among NHRs against SARS-CoV-2 in the US.
Federal, private, and academic partners evaluated routinely obtained care data of 196 community-based NHs across 19 US states. Sixty-day VE estimates of second booster doses were calculated among NHRs previously administered three COVID-19 vaccinations. The study population was administered the second booster dose between March 29th and June 15th 2022. It was followed up till July 25th, 2022, during the period of the SARS-CoV-2 Omicron variant’s BA.2 subvariant, BA.2.12.1 subvariant (between March and June 2022), and Omicron BA.4/5 subvariants’ (July 2022) predominance.
The study included NHRs if they had lived in NHs for more than 100 days with less than ten days outside the care facility, if they had received triple mRNA SARS-CoV-2 vaccinations before the commencement of the study, and if they were not vaccinated in the previous three months of the study. NHRs were excluded from the analysis in the case of prior SARS-CoV-2 exposure within the previous one month of the study’s index date, if they had been treated with monoclonal antibodies (mAbs) during the previous three months, or were hospice care recipients.
Data on the status of COVID-19 vaccinations were obtained from the NHRs’ electronic health-related records. Propensity score matching (PSM) was performed for 1:1 case-control matching. The study outcomes analyzed were (i) incident COVID-19 cases, confirmed by RT-PCR (reverse transcription–polymerase chain reaction) tests or rapid antigen tests, (ii) SARS-CoV-2–associated hospitalizations, (iii) deaths within a month of incident SARS-CoV-2 infections, and (iv) severe SARS-CoV-2 infection outcomes (a combined measure of hospitalizations or deaths).
Logistic regression modeling was used for the analysis with data adjustments for age, prior COVID-19 history, comorbidities, and immunocompromised disorders, hospitalizations within the previous three months, the time elapsed since the most recent SARS-CoV-2 vaccination, nursing home stay duration, and influenza vaccination history.
In total, 9,527 residents were analyzed, with a median count of 49 NHRs in each NH, among which, 34% (n=3,245) of residents were administered the second vaccine booster during the present analysis period. After PSM, 1,343 NHRs were excluded due to a lack of matched controls. The average age of the participants was 78 years, and the average NH stay duration was 880 days, with a median of 196 days elapsed since the most recent SARS-CoV-2 vaccinations, 36% male individuals and four comorbidities based on the Charlson index.
Compared to a single booster dose, the 60-day vaccine effectiveness for the second booster was 26% against SARS-CoV-2 infection, 60% against hospitalizations, 90% against deaths, and 74% against the composite outcome for COVID-19 severity.
Overall, the study findings showed that second booster mRNA COVID-19 vaccinations conferred additional immune benefit over the first booster vaccination against COVID-19 severity outcomes during Omicron predominance. Care facilities must ensure that NHRs remain updated with recommended booster doses for SARS-CoV-2 vaccinations to prevent COVID-19 severity outcomes.
The study has several limitations. Point-type estimates obtained in the present study were comparable to those documented in previous analyses; however, the number of hospitalizations was too low to attribute the decrease to COVID-19 vaccinations in a definite manner. Some NHRs may have been less likely to be admitted to hospitals even with severe SARS-CoV-2 infections, therefore, excluding null effects to prevent hospitalizations alone.
Further, deaths alone are also problematic since if NHRs are admitted to hospitals, their deaths may not be recorded in the NH records. The impact of a single NHR’s vaccination on the VE estimates for the other NHRs was not considered in the present study. Therefore, the direct vaccination effects may be underestimated. Lastly, due to short 60-day follow-ups, the potential waning of the booster vaccination-induced antibodies could not be determined.