COVID-19 outbreaks during or shortly after vaccination of care home residents: summary of three studies from the US and Germany

Evidence summary by Sian Smith, Maximilian Salcher-Konrad, Adelina Comas-Herrera (Care Policy and Evaluation Centre, London School of Economics and Political Science)

This summary covers three studies of care homes that experienced outbreaks following Pfizer/ BioNTech vaccination demonstrate the vulnerability of care home populations in the period until vaccines develop their full protective effect and make the case for prioritising the completion of both doses. 

Key findings:

  • In a small study of two Connecticut (US) nursing homes (463 residents overall) from December 2020 – February 2021, administration of the first dose of the vaccine was found to have 63% effectiveness against infection. After vaccinations started, 97 cases were detected, mostly during the start of the investigation period. 
  • In a single-centre study of an outbreak in a Kentucky (US) nursing home, 26 of 83 (31%) residents and 20 of 116 (17%) staff tested positive for SARS-CoV-2 after >90% of residents and >50% of staff had been vaccinated. Unvaccinated residents and staff were 3 to 4 times as likely to be infected compared to those who were vaccinated. While some of the infections occurred in residents and staff >14 days after they had received their second dose, vaccine effectiveness was overall substantial (66% and 76% against infections among residents and staff, respectively; 87% against symptomatic illness in both residents and staff; and 94% against hospitalisations and death among residents). 
  • A single-centre study of a German care home (76 residents) reported an outbreak in January 2021 after 96% of residents and 90% of employees were vaccinated with a single dose. 26/76 (34%) residents had positive PCR COVID-19 tests following serial PCR testing, with a case fatality rate of 35%. No new cases were detected 23 days after the 1st dose (2 days after booster dose). 

Social Care COVID Recovery and Resilience project view on the meaning of these studies: 

  • The existence of outbreaks in care homes following the administration of one to two doses of the Pfizer/ BioNTech vaccine highlights the continued risk for this population in the period immediately following the start of vaccination drives in care homes. 
  • As shown in previous, larger-scale studies, there is a time-lag between vaccination administration and the strong protective effect of vaccines. In addition, these three case studies demonstrate the potential for widespread infection affecting up to one third of the vaccinated population of a care home until the vaccine has developed its protective effect. 
  • The three studies support the view that administering the full two doses of vaccination should be the priority amongst vulnerable populations. 

The three studies are summarised in more detail below.

Study summaries: 

  1. Effectiveness of the Pfizer-BioNTech COVID-19 Vaccine Among Residents of Two Skilled Nursing Facilities Experiencing COVID-19 Outbreaks — Connecticut, December 2020–February 2021

Study authors: Amadea Britton, Kara M. Jacobs Slifka, Chris Edens, Srinivas Acharya Nanduri, Stephen M. Bart, Nong Shang, Adora Harizai, Jillian Armstrong, Kerui Xu, Hanna Y. Ehrlich, Elizabeth Soda, Gordana Derado, Jennifer R. Verani, Stephanie J. Schrag, John A. Jernigan, Vivian H. Leung, Sunil Parikh

Study summary:

A study of two nursing homes in Connecticut from December 2020 – February 2021, experiencing COVID-19 outbreaks following Pfizer/ BioNTech vaccine administration amongst residents and staff.

Electronic chart reviews were done to collect information on vaccination status and infection from the first day of vaccination in both facilities (463 residents: 142 (31%) facilities A and 321 (69%) facility B). Following detection of first case, both facilities conducted PCR testing weekly (facility A) or twice-weekly (facility B) for residents and regular testing for staff. 

Key findings:

  • The study found that the effectiveness of the first dose against infection was 63% (95% confidence interval [CI] = 33%–79%). This was measured as the protective effect in the period >14 days after 1stdose through 7 days after 2nd dose.
  • 97 cases occurred from the day vaccinations were first administered: 40 (41%) in facility A, 57 (59%) in facility B, with most cases occurring during the start of the investigation period. 
  • 25% of residents who were part of the study had confirmed past COVID-19 infection. 

Study limitations reported by the authors:

  • The small sample size did not allow for the estimation of the vaccine effectiveness of a 2nd dose, with no assessment of hospitalisations, symptomatic illness, death or other endpoints. 
  • Limited generalisability due to sample size and an underrepresentation of ethnic minorities.
  • There was potential for unmeasured or unrecognised cofounders such as past, undetected infection.  

Study authors: Alyson M. Cavanaugh, Sarah Fortier, Patricia Lewis, Vaneet Arora, Matt Johnson, Karim George, Joshua Tobias, Stephanie Lunn, Taylor Miller, Douglas Thoroughman, Kevin B. Spicer

In this study from a skilled nursing facility in Kentucky (US), the authors describe a COVID-19 outbreak that started on 1 March 2021, after 75 of 83 residents (90.4%) and 61 of 116 staff (52.6%) had received two doses of the BioNTech / Pfizer vaccine.

After most residents and staff received their vaccines in January 2021, an outbreak was identified through routine antigen testing of an unvaccinated member of staff on 1 March 2021. Subsequently, all residents were tested daily (later reduced to twice weekly), and staff tested twice weekly. The authors calculated relative risks and vaccine effectiveness, comparing those who had received the vaccine to those who had not.

Key findings:

  • Among 83 residents and 116 staff, a total of 46 cases were detected during the outbreak (26 residents, 20 staff).
  • Among 71 fully vaccinated residents (i.e., they had received the 2nd dose >14 days before), 18 (25%) were infected, 6 of them symptomatic and 1 died. In contrast, 8 residents were fully unvaccinated (no dose received): 6 of those were infected, 5 symptomatic, and 2 died. This resulted in vaccine effectiveness estimates of 66.2% (95% CI 40.5–80.8) against infection, 86.5% (95% CI 65.6–94.7) against symptomatic illness, and 94.4 (95% CI 44.6–99.4) against death.
  • Among staff, 56 staff were fully vaccinated and 4 (7%) were infected (none died). Comparing outcomes against 54 unvaccinated staff gave vaccine effectiveness estimates of 75.9% against infection (95% CI 32.5–91.4) and 87.1% (95% CI 46.4–96.9) against symptomatic disease.
  • Whole genome sequencing identified a new variant (R.1) previously unknown in Kentucky.

Study limitations:

  • Vaccine effectiveness estimates were not adjusted for baseline health status. Poorer baseline health may have been a predictor for not receiving the vaccine, potentially biasing the estimate of the protective effect on hospitalisations and deaths.
  • Surveillance testing was performed using antigen tests, which have reduced sensitivity to detect asymptomatic cases.
  • Single-centre study with limited generalisability.

Study authors: Dirk Westhölter, Christian Taube

In this small study of one German care home (76 residents), the authors report on an COVID-19 outbreak amongst residents following vaccination with a singular dose of BioNTech/ Pfizer of 96% residents and 90% employees.  

A staff member and member of the vaccination team reported respiratory symptoms 1-4 days after vaccination, testing positive for COVID-19 via PCR test. Subsequent PCR testing was conducted of all residents on days 7, 14, 20, 23, 27, 30 and 35 after 1st vaccination dose alongside strict quarantining policies. All asymptomatic residents were offered a boosting dose of BioNTech/ Pfizer 21 days after 1st dose. 

Key findings:

  • 26/76 (34%) residents had positive PCR COVID-19 tests following serial PCR testing.
  • 1 case was detected after 7 days, 10 cases after 14 days, 12 cases after 20 days and 3 after 23 days following the 1st vaccination dose. Only 3/26 positive residents were symptomatic at time of diagnosis and 12/26 developed symptoms later.
  • Mortality was 9/26 infections (35%), 5/9 were diagnosed on day 20. 
  • There were 3 unvaccinated residents in the nursing home. All 3 tested positive but showed mild symptoms.
  • No new cases 23 days after 1st dose (2 days after booster dose). 
  • Measured low CT values and high mortality which was consistent with ‘natural’ COVID-19, not vaccine-attenuated. 

Study limitations:

  • Single centre, therefore limited generalisability.

To cite this summary:

Smith S., Salcher-Konrad M. and Comas-Herrera A. (2021) COVID-19 outbreaks during or shortly after vaccination of care home residents: summary of three studies from the US and Germany., International Long-Term Care Policy Network, CPEC-LSE, 4th May 2021.

Summary by Sian Smith, Maximilian Salcher-Konrad, and Adelina Comas-Herrera, carried out as part of the?Social Care COVID Recovery and Resilience Project?(funded by the National Institute for Health Research (NIHR) Policy Research Programme (NIHR202333). The views expressed in this summary are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care). 

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