A recent study has examined the response of nursing home residents who were naïve to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection following vaccination by the mRNA BNT162b2 model from Pfizer-BioNTech.

The researchers found that residents who were never exposed to SARS-CoV-2 showed four-fold lower median neutralizing antibody titers, and half the anti-spike level, than naïve healthcare workers.

Since the start of the pandemic, nursing homes have been highly vulnerable to coronavirus transmission. Older adults are also at high risk of developing severe coronavirus disease 2019 (COVID-19)-related hospitalization and mortality.

The currently approved vaccinations have helped reduce the risk of hospitalization and mortality and have prioritized vaccines for people over 65. However, the Pfizer vaccine clinical trials did not specifically test nursing home residents who are more likely to have multiple comorbidities, medications that could alter long-term immunity.

The researchers write:

[Nursing home] residents’ blunted antibody responses have important implications regarding the quality and durability of protection afforded by neoantigen vaccines. We urgently need better longitudinal evidence on vaccine effectiveness specific to [nursing home] resident populations to inform best practices for [nursing home] infection control measures, outbreak prevention, and potential indication for a vaccine boost.”

The study “Reduced BNT162b2 mRNA vaccine response in SARS-CoV-2-naive nursing

home residents” is available as a preprint on the medRxiv* server, while the article undergoes peer review.

How they did it

The study recruited 149 nursing home residents who were or were not previously exposed to SARS-CoV-2 infection and who were scheduled to get vaccinated with the Pfizer-BioNTech vaccine. Participants were 48 to 99 years old. They were compared to 111 health care workers with a median of 48 years and an unvaccinated convalescent group 29-94 days after recovering from asymptomatic or mild infection with a median age of 53 years.

Blood samples before vaccination were collected from all nursing home residents and about 64% of healthcare workers. They were sampled again approximately 14 days after receiving their second Pfizer dose. They measured the amount of immunoglobulin G (IgG) specific to SARS-CoV-2’s spike protein and its receptor-binding domain (RBD).

Results

Compared to healthcare workers who were never exposed to SARS-CoV-2, nursing home residents had a lower antibody response with four-fold lower median neutralization titers. Nursing home residents had a neutralization titer of about 135, while healthcare workers showed titers of about 521. There was also half the anti-spike level in nursing home residents than in healthcare workers.

About 17% of nursing home residents who were never exposed to SARS-CoV-2 had lower neutralizing titers at or below the lower detection limit. Meanwhile, only 1.3% of healthcare workers who were never exposed to SARS-CoV-2 experienced low neutralizing titers.

Only 36% of nursing home residents with no prior SARS-CoV-2 exposure had high neutralization titers compared to the 85% in unvaccinated SARS-CoV-2 convalescent younger adults with previous exposure.

However, nursing home residents who recovered from COVID-19 infection showed similar neutralization, anti-spike, and anti-RBD titers to vaccinated healthcare workers who also recovered from prior illness.

If validated through peer-review, these findings could help inform vaccination strategies and measures aimed at preventing viral transmission.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Jocelyn Solis-Moreira

Jocelyn Solis-Moreira graduated with a Bachelor's in Integrative Neuroscience, where she then pursued graduate research looking at the long-term effects of adolescent binge drinking on the brain's neurochemistry in adulthood.