The coronavirus disease 2019 (COVID-19), caused by infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), frequently causes severe disease in the elderly and patients with certain comorbidities.
In long-term care facilities (LTCFs), the mortality rate of COVID-19 throughout much of the pandemic was often higher than the rest of the population. This led to the prioritization of LTCF residents during vaccine roll-out; however, there is little data on the vaccine effectiveness (VE) of this group.
Study: COVID-19 outbreak in an elderly care home: very low vaccine effectiveness and late impact of booster vaccination campaign. Image Credit: Suwin / Shutterstock.com
A new Vaccine study examines an outbreak of the SARS-CoV-2 Delta variant in a Dutch LTCF that continued to infect individuals and cause severe disease even after containment measures were implemented and a vaccine booster campaign was instituted. The aim of this study was to assess primary VE against infection and mortality due to COVID-19, with a particular focus on booster vaccine effectiveness.
Introduction
Elderly people residing in LTCFs are at high risk for severe COVID-19 due to shared living spaces that promote the transmission of SARS-CoV-2, low immunologic function, and coexisting illnesses such as dementia, heart disease, and chronic lung disease. LTCF residents are rarely brought to community testing centers for COVID-19 screening and are not frequently hospitalized.
While LTCF residents were given priority vaccinations, earlier studies reported that immunity waned quite rapidly from 12 weeks post-immunization. The paucity of data on VE thereafter makes it difficult to devise appropriate booster dose guidelines in this patient population.
The current study reports an LTCF outbreak among both staff and residents. The Netherlands facility had two somatic wards and two wards for patients with psychiatric illness and/or extreme old age. These four wards accounted for 63 residents.
Additionally, 88 residents lived at three assisted living semi-detached housing facilities. These residents could use the same daycare and restaurant rooms as those in the wards, with most of the 42 residents at one of these facilities participating in these activities.
This left residents at the other two housing estates, whereas the staff and individual housing facilities were relatively secluded from common facilities. Taken together, a total of 160 staff were working at the time of the outbreak, with 151 residents in total.
The first COVID-19 case occurred in one of the psycho-geriatric wards in a fully vaccinated patient following contact with an infected individual. Thereafter, testing was carried out for all ward patients and staff, as well as close contacts, both immediately and on day five from the last exposure.
All infected residents were quarantined until they were asymptomatic for 24 hours or at least seven days from symptom onset, with others using personal protective equipment (PPE). Visitors without COVID-19 symptoms were required to wear face masks.
Following initial room-level isolation of cases, the entire ward, including staff and patients, was isolated as the outbreak grew. This was followed by further cases outside the ward, including staff. These workers, as well as the wards they currently worked in, were also quarantined.
At this point, visits were prohibited, common areas closed, and other daily activities restricted. Booster vaccine doses were administered on December 6, 2021, to all ward patients and many in the adjacent housing estates who were still negative for COVID-19.
New COVID-19 cases appeared in all LTCF wards and housing estate with social interactions with the LTCF. Testing and individual isolation measures were implemented, with all common areas shut down.
The outbreak, which began on November 20, 2021, was ultimately contained when the last case was discharged from isolation on December 22, 2021.
Study findings
The ward and affected housing estate comprised 105 residents, with a median age of 85 years and two-thirds female. While 13 had a history of COVID-19 and eight were unvaccinated, all other residents were fully vaccinated, with the last dose having been taken on or before July 6, 2021. All residents who did not get infected with SARS-CoV-2 during the current outbreak received a booster dose in December.
A total of 70 cases were reported among LTCF residents, with an overall attack rate (AR) of 67%. The initially affected ward had a much higher AR of 94%, followed by 80% for one somatic ward. The AR for the affected housing estate was 62%.
All COVID-19 cases were caused by the SARS-CoV-2 Delta variant. The VE of primary vaccination against this strain was 17% and 70% against mortality within 30 days. Interestingly, this was unaffected by a history of prior COVID-19, perhaps due to the small number of only 13 of the 105 patients who were previously infected.
Among unvaccinated patients, the case fatality rate was 33% as compared to 12% in fully vaccinated residents. Few cases were reported from six days after booster doses were given. No boosted patients died from COVID-19.
Implications
The high rate of infection in a fully vaccinated population, despite isolation and containment measures, adds to current knowledge about the limitations of primary vaccination. The second vaccine dose was taken six or more months prior to the outbreak in this study.
Complete vaccination provided 17% protection against infection; however, it reduced mortality by 70% as compared to the unvaccinated. Thus, a third of unvaccinated cases ended in death as compared to 12% among the fully vaccinated.
The high AR in the vaccinated subgroup could be due to repeated exposures, exposure to a high viral load, or a new SARS-CoV-2 variant that evaded vaccine-induced immunity. Household ARs are consistently higher than community ARs, possibly due to increased exposure. This could explain the current findings within the self-contained environment of an LTCF.
In fact, there were only five cases among the 30 residents who remained susceptible to SARS-CoV-2 but received a booster dose. Each of these occurred in the second week following receipt of the booster dose. No cases were reported in the third week.
The researchers believe that timely booster doses helped arrest the outbreak. Nevertheless, a third of the boosted patients already had hybrid immunity with a history of prior COVID-19.
[These findings] highlight the vulnerability of adults living in LTCF and the need for timely booster vaccinations.”
Booster vaccine doses appear to take effect only seven or more days from the day of administration in this population group. Once active, the resulting immunity may prevent further transmission of SARS-CoV-2.
The small sample size in the current study indicates the need for larger studies in the future to validate these inferences.
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