Why Do We Continue to See COVID-19 Outbreaks in Fully Vaccinated Care Homes?

The Charité researchers analyzed blood samples from older and younger individuals who had received their vaccinations and tested for the presence of SARS-CoV-2 specific antibodies (including immunoglobulin G or IgG). Credit: © Charité | Victor Corman

SARS-CoV-2 outbreaks have been reported across Germany involving care homes with fully vaccinated residents. To better understand this phenomenon, a team of researchers from Charité – Universitätsmedizin Berlin used an outbreak in a Berlin facility to analyze virus-related data and study the immune responses of elderly residents after vaccination. The researchers’ data, published in Emerging Infectious Diseases, confirms the vaccine’s efficacy in the elderly. However, they also indicate a delayed and slightly reduced immune response. In light of their findings, the researchers emphasize the need to vaccinate both healthcare providers and close contacts to better protect this high-risk group.

The BioNTech/Pfizer COVID-19 vaccine has demonstrated a high level of efficacy. Pre-approval studies have shown that the vaccine can prevent more than 90 percent of symptomatic SARS-CoV-2 infections as early as one week after the second dose. The vaccine’s efficacy was later confirmed in observational, population-based studies. Despite this efficacy, infections will occasionally develop in vaccinated individuals. But what could explain the occurrence of larger outbreaks in care homes whose residents have been fully vaccinated? What medical experts suspected based on past experience with other vaccines has now been confirmed by two linked studies, both conducted by an interdisciplinary team of Charité researchers. These studies showed that the immune system’s response to vaccination is less effective in the elderly than in younger individuals.

The researchers initially studied an outbreak discovered in February 2021 at a Berlin-based long-term care facility. SARS-CoV-2 infections were detected in 11 health care personnel who had not been fully vaccinated and in 20 residents, all but four of whom had received doses of the BioNTech/Pfizer vaccine. While the four unvaccinated individuals developed symptoms severe enough to require hospitalization, only a third of the fully vaccinated individuals showed respiratory symptoms such as coughing and shortness of breath.

An analysis of individual swabs showed that vaccinated individuals tended to have lower concentrations of SARS-CoV-2 in their throats than unvaccinated individuals. Similarly, the mean duration of SARS-CoV-2 shedding was shorter in vaccinated individuals than in unvaccinated individuals, approximately 8 and 31 days, respectively. Despite the outbreak, four vaccinated residents remained free of the virus. While containment measures were successful in preventing spread to other parts of the facility, two of the 16 vaccinated COVID-19 patients had to be hospitalized. One of the hospitalized patients died after a hypertensive crisis that led to a cerebral hemorrhage. A second patient died in the care home, but had tested negative for the virus for more than two weeks before her death. Since neither of these two patients ever developed respiratory symptoms, the researchers suspected no causal relationship with SARS-CoV-2.

“Vaccination certainly provided protection for the care home residents involved in this outbreak and dramatically reduced the severity of the disease,” said one of the study’s three lead authors, Dr. Victor Corman, deputy director of the National Consultant Laboratory for Coronaviruses of the Department of Virology and a researcher at the German Center for Infection Research (DZIF). He adds: “It is also likely that the shorter shedding duration was responsible for the prevention of further infections. However, the high number of infections observed makes it clear that even when a vaccine has a high level of efficacy, this does not always occur. translates into complete protection for the elderly.”

One possible reason for this, the researchers say, is that the outbreak was caused by the Alpha variant (formerly known as B.1.1.7), which is associated with higher viral loads in the throat and greater transmissibility. The researchers also identified a second reason: the way an individual’s immune system responds to vaccination with the BioNTech/Pfizer vaccine. To test their hypothesis, the researchers compared a cohort of elderly patients (over 70 years of age and enrolled in a private primary care practice) with a younger cohort of Charité staff (mean age 34 years). Blood tests taken just three weeks after the first dose showed that about 87 percent of the younger cohort had developed antibodies to SARS-CoV-2. In the older cohort this was about 31 percent. One month after the second dose, almost the entire cohort of youth (99 percent) tested positive for SARS-CoV-2 specific antibodies. In the older cohort this was about 91 percent. Antibodies also take longer to mature in the older age groups, meaning their ability to bind to the virus was reduced. Even T-cell-mediated immunity, the second major branch of the body’s immune response, was found to be weaker.

Summarizing the team’s findings, Prof. Dr. Leif Erik Sander, vaccine researcher at Charité’s Department of Infectious Diseases and Respiratory Medicine, said: “Our study shows that there is a significant delay in the body’s immune response after vaccination in the elderly, and that this response never reaches the level seen in young people.” He adds: “Of course you can’t determine the effectiveness of vaccination on the basis of a single outbreak. Since the start of the vaccination campaign, there has been a dramatic overall decline in the number of infections in care homes. However, outbreaks occasionally occur and the elderly appear to be more susceptible than younger people because their immune response appears to be slightly weaker.

The study’s third lead author, PD Dr. Florian Kurth of the Department of Infectious Diseases and Respiratory Medicine, emphasizes the importance of the findings: “While only about one in ten fully vaccinated people over the age of 70 have no antibodies in their blood, individuals with low vaccine-induced vaccines are currently unable to identify immunity. Therefore, if we want to protect this risk group, we cannot rely solely on vaccination. As large parts of the population remain without immunity, both infection control measures and testing will continue to play an important role for the foreseeable future. Obviously, vaccination of both healthcare staff and visitors is critical to prevent future outbreaks in care homes. In the not too distant future, we will probably also see booster shots that can be used to improve immunity in the elderly.”

References:

“Outbreak of SARS-CoV-2 B.1.1.7 Lineage after vaccination in a long-term care facility, Germany, February-March 2021” by Pinkus Tober-Lau, Tatjana Schwarz, David Hillus, Jana Spieckermann, Elisa T. Helbig, Lena J. Lippert, Charlotte Thibeault, Willi Koch, Leon Bergfeld, Daniela Niemeyer, Barbara Mühlemann, Claudia Conrad, Stefanie Kasper, Friederike Münn, Frank Kunitz, Terry C. Jones, Norbert Suttorp, Christian Drosten, Leif Erik Sander, Florian Kurth and Victor M. Corman, Emerging Infectious Diseases.
DOI: 10.3201/eid2708.210887

“Delayed Antibody and T Cell Response to BNT162b2 Vaccination in the Elderly, Germany” by Tatjana Schwarz, Pinkus Tober-Lau, David Hillus, Elisa T. Helbig, Lena J. Lippert, Charlotte Thibeault, Willi Koch, Irmgard Landgraf, Janine Michel Leon Bergfeld, Daniela Niemeyer, Barbara Mühlemann, Claudia Conrad, Chantip Dang-Heine, Stefanie Kasper, Friederike Münn, Kai Kappert, Andreas Nitsche, Rudolf Tauber, Sein Schmidt, Piotr Kopankiewicz, Harald Bias, Joachim Seyvon Kalle, Terry C. , Norbert Suttorp, Christian Drosten, Leif Erik Sander, Victor M. Corman and Florian Kurth, Emerging infectious diseases.
DOI: 10.3201/eid2708.211145