Effectiveness of Up-to-Date COVID-19 Vaccination in Preventing SARS-CoV-2 Infection Among Nursing Home Residents — United States, November 20, 2022–January 8, 2023

Nursing home residents have been disproportionately affected by the COVID-19 pandemic; their age, comorbidities, and exposure to a congregate setting has placed them at high risk for both infection and severe COVID-19–associated outcomes, including death (1). Receipt of a primary COVID-19 mRNA vaccination series (2) and monovalent booster doses (3) have been demonstrated to be effective in reducing COVID-19–related morbidity and mortality in this population. Beginning in October 2022, the National Healthcare Safety Network (NHSN) defined up-to-date vaccination as receipt of a bivalent COVID-19 mRNA vaccine dose or completion of a primary series within the preceding 2 months.* The effectiveness of being up to date with COVID-19 vaccination among nursing home residents in preventing SARS-CoV-2 infection is not known. This analysis used NHSN nursing home COVID-19 data reported during November 20, 2022–January 8, 2023, to describe effectiveness of up-to-date vaccination status (versus not being up to date) against laboratory-confirmed SARS-CoV-2 infection among nursing home residents. Adjusting for calendar week, county-level COVID-19 incidence, county-level social vulnerability index (SVI), and facility-level percentage of staff members who were up to date, up-to-date vaccine effectiveness (VE) against infection was 31.2% (95% CI = 29.1%–33.2%). Nursing home residents should stay up to date with recommended age-appropriate COVID-19 vaccination, which now includes an additional bivalent vaccine dose for moderately or severely immunocompromised adults aged ≥65 years to increase protection against SARS-CoV-2 infection.

The Centers for Medicare & Medicaid Services (CMS) requires CMS-certified nursing homes to submit incident COVID-19 case and vaccination data to NHSN each week.^†,§ Data include the number of infections (defined as laboratory-confirmed^¶ SARS-CoV-2 infections) stratified by patient vaccination status, and the number of residents in the nursing home (with a stay of ≥24 hours) stratified by vaccination status.** During the study period, NHSN defined up-to-date vaccination status as 1) ever having received a COVID-19 mRNA bivalent vaccine dose, or 2) completion of a primary series <2 months earlier. The number of residents who were not up to date was calculated by subtracting the number who were up to date from the total number of residents in the facility. Residents who were not up to date included those who 1) previously received monovalent booster doses but did not receive a bivalent vaccine dose, 2) received the primary series >2 months earlier but did not receive any subsequent doses, 3) received 1 dose of the primary series, or 4) did not receive any COVID-19 vaccine doses.

NHSN analyzed weekly COVID-19 case and up-to-date vaccination status data for CMS-certified nursing homes during November 20, 2022–January 8, 2023. The study period was chosen to coincide with both the inclusion of bivalent vaccine in the definition of up-to-date status and the increase in COVID-19 infections during the winter months.^†† The study included data submitted by CMS-certified nursing homes that reported both COVID-19 cases and up-to-date vaccination status for each week during the study period.

Analysts merged weekly incident case counts (stratified by up-to-date vaccination status) with weekly resident counts (stratified by up-to-date vaccination status) each week during the study period. Nursing homes that reported no data on up-to-date vaccination status throughout the study period were excluded, as were those that did not meet standard data quality criteria.^§§ Resident-weeks were calculated by aggregating the number of residents who spent ≥1 day at the facility during the week of data collection over the study period.

The ratio of infection between residents who were up to date and those who were not was determined using a zero-inflated negative binomial mixed model (4) to evaluate associations with acquisition of COVID-19, while adjusting for potential confounders. The model used data collected by NHSN and included nursing home as a random effect to account for between-facility variability. Covariates included in models were factors known to be associated with either up-to-date vaccination status or infection, including calendar week, SVI, county-level incidence, and percentage of facility staff members who were up to date with COVID-19 vaccination. VE against infection was estimated as 1 − rate ratio x 100. Analyses were performed using SAS software (version 9.4; SAS Institute) and R software (version 4.0.3; R Foundation). This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.^¶¶

The analysis included 108,727 weekly reports from 14,464 nursing homes. Overall, 4,314,714 (48.1%) nursing home resident-weeks were up to date, and 52,853 (40.6%) of COVID-19 patients were up to date. The resulting crude infection rate among up-to-date residents was 12.3 per 1,000 resident-weeks (95% CI = 12.2–12.4) compared with 16.6 per 1,000 resident-weeks (95% CI = 16.5 –16.7) among residents who were not up to date. During the study period, the weekly percentage of residents who were up to date increased from 44.2% to 51.2%.

Each week, COVID-19 incidence among nursing home residents who were up to date (7.6–15.3 cases per 1,000 residents) was lower than incidence among those who were not up to date (11.1–19.1 cases per 1,000 residents) (Figure). The adjusted rate ratio of SARS-CoV-2 infection among residents who were up to date compared with those not up to date was 0.69 (95% CI = 0.67–0.71). Among nursing home residents with up-to-date vaccination, VE against infection was 31.2% (95% CI = 29.1%–33.2%) (Table).

Acknowledgments

Sushmitha Ananth, Sherese Dennard, Katherine Fleming-Dutra, Emily Haanschoten, Lori Haas, Elizabeth Kalayil, Hoody Lymon, Darielle Oliver, Audrey Robnett-Brown, Theresa Rowe, George Segovia, Shanjeeda Shafi, Jolie Siegel.

Corresponding author: Emily Wong, vtu4@cdc.gov.

¹Division of Healthcare Quality Promotion, National Center for Emerging and Zoonotic Infectious Diseases, CDC; ²Goldbelt C6, Chesapeake, Virginia; ³National Center for Immunization and Respiratory Diseases, CDC; ⁴Lantana Consulting Group, East Thetford, Vermont.

References

1. Su Z, McDonnell D, Li Y. Why is COVID-19 more deadly to nursing home residents? QJM 2021;114:543–7. https://doi.org/10.1093/qjmed/hcaa343 PMID:33453109
2. Bagchi S, Mak J, Li Q, et al. Rates of COVID-19 among residents and staff members in nursing homes—United States, May 25–November 22, 2020. MMWR Morb Mortal Wkly Rep 2021;70:52–5. https://doi.org/10.15585/mmwr.mm7002e2 PMID:33444301
3. Prasad N, Derado G, Nanduri SA, et al. Effectiveness of a COVID-19 additional primary or booster vaccine dose in preventing SARS-CoV-2 infection among nursing home residents during widespread circulation of the Omicron variant—United States, February 14–March 27, 2022. MMWR Morb Mortal Wkly Rep 2022;71:633–7. https://doi.org/10.15585/mmwr.mm7118a4 PMID:35511708
4. Yau KKW, Wang K, Lee AH. Zero-inflated negative binomial mixed regression modeling of over-dispersed count data with extra zeros. Biom J 2003;45:437–52. https://doi.org/10.1002/bimj.200390024
5. Dubendris H, Reses HE, Wong E, et al. Laboratory-confirmed COVID-19 case incidence rates among residents in nursing homes by up-to-date vaccination status—United States, October 10, 2022–January 8, 2023. MMWR Morb Mortal Wkly Rep 2023;72:95–9. https://doi.org/10.15585/mmwr.mm7204a3 PMID:36701262
6. Link-Gelles R, Ciesla AA, Fleming-Dutra KE, et al. Effectiveness of bivalent mRNA vaccines in preventing symptomatic SARS-CoV-2 infection—Increasing Community Access to Testing Program, United States, September–November 2022. MMWR Morb Mortal Wkly Rep 2022;71:1526–30. https://doi.org/10.15585/mmwr.mm7148e1 PMID:36454688
7. Rosenblum HG, Wallace M, Godfrey M, et al. Interim recommendations from the Advisory Committee on Immunization Practices for the use of bivalent booster doses of COVID-19 vaccines—United States, October 2022. MMWR Morb Mortal Wkly Rep 2022;71:1436–41. https://doi.org/10.15585/mmwr.mm7145a2 PMID:36355612
8. Britton A. COVID-19 vaccine effectiveness updates. Presented at the Advisory Committee on Immunization Practices meeting, Atlanta, GA; February 24, 2023. https://stacks.cdc.gov/view/cdc/125167
9. Link-Gelles RL. COVID-19 vaccine effectiveness updates. Presented at the Advisory Committee on Immunization Practices meeting, Atlanta, GA; April 19, 2023. https://stacks.cdc.gov/view/cdc/127296
10. Link-Gelles R, Weber ZA, Reese SE, et al. Estimates of bivalent mRNA vaccine durability in preventing COVID-19–associated hospitalization among adults with and without immunocompromising conditions—VISION Network, September 2022–April 2023. MMWR Morb Mortal Wkly Rep 2023;72:579–88. https://doi.org/10.15585/mmwr.mm7221a3 PMID:37227984

FIGURE. SARS-CoV-2 infections per 1,000 nursing home residents,* by up-to-date vaccination status^† and reporting week — National Healthcare Safety Network, United States, November 20, 2022–January 8, 2023

* With 95% CIs indicated by error bars.

^† Up-to-date vaccination status was defined as 1) ever having received a bivalent vaccine dose or 2) primary series completed <2 months earlier. The number of residents who were not up to date was calculated by subtracting the number of up-to-date residents from the total number of residents in the facility and included those who 1) received monovalent booster doses but did not receive a bivalent vaccine dose, 2) received the primary series >2 months earlier but did not receive any subsequent doses, 3) received 1 dose of the primary series, or 4) did not receive any COVID-19 vaccine doses.

Abbreviations: Ref = referent group; RR = rate ratio; VE = vaccine effectiveness.
* Up-to-date vaccination status was defined as 1) ever having received a bivalent vaccine dose or 2) completed a primary series <2 months earlier. The number of residents who were not up to date was calculated by subtracting number of up-to-date residents from the total number of residents in the facility and included those who 1) received monovalent booster doses but did not receive a bivalent vaccine dose, 2) received the primary series >2 months earlier but did not receive subsequent doses, 3) received 1 dose of the primary series, or 4) did not receive any COVID-19 vaccine doses.
^† Resident-weeks were the number of residents staying in a facility for ≥1 day during the week of data collection aggregated to the study period, stratified by vaccination status reported by nursing homes.
^§ Cases were the aggregate of weekly case counts stratified by vaccination status reported by nursing homes. Cases among residents up to date were defined as infections in residents who became up to date ≥14 days before a positive SARS-CoV-2 test result. Cases who became up to date <14 days before a positive SARS-CoV-2 test result were included in the not up-to-date group.
^¶ Infections per 1,000 resident-weeks.
** RR results from zero-inflated negative binomial mixed model.
^†† VE was estimated as 1 − RR x 100.