A new Irish study involving older residents of nursing homes has found that while Covid-19 antibody levels predictably declined over time, this decline was particularly striking in those who had never been infected with the SARS-CoV-2 virus.

According to the researchers, their findings provide strong support for the use of booster vaccines among this cohort.

The study – NH-COVAIR - involved immunologists, geriatricians and nurses from Trinity College Dublin (TCD), Tallaght University Hospital (TUH) and several translational research laboratories.

They assessed the levels of Covid-19 antibodies against the SARS-CoV-2 spike protein before vaccination, five weeks after two doses of the Pfizer vaccine and then six months after.

The study found that previous Covid-19 infection, age and degree of frailty were all associated with six-month antibody levels post-vaccine. While antibody levels predictably declined over time, this decline was particularly noticeable in those individuals with no previous evidence of SARS-CoV-2 infection. 

Furthermore, whereas previous infection was associated with much greater levels of anti-spike antibodies at six months, increasing age and greater levels of frailty were independently associated with lower antibody levels.

Importantly, antibody levels were significantly associated with neutralisation capacity – that is the ability of antibodies to neutralise the SARS-CoV-2 virus.

These findings highlight the effect past infection has on shaping long-term antibody responses in older nursing home residents and support the ongoing use of booster vaccinations in this population.

The research also suggests that SARS-CoV-2-naïve individuals may be particularly vulnerable, although it should be noted that the study only considered anti-spike antibody levels and did not examine long-term “memory” immune cells and the ability of these to fight off future infection.

This is, however, an area of ongoing research for this research group. 

“Our findings demonstrating lower antibody levels in SARS-CoV-2-naïve individuals and in those with increasing age and frailty tell only part of the story, but they support the ongoing use of vaccine boosters in this vulnerable population,” commented the study’s lead author, Dr Adam Dyer, a specialist registrar in geriatric medicine and Irish clinical academic training fellow in TCD’s School of Medicine and TUH.

The importance of boosters was also highlighted by principal investigator, Prof Sean Kennelly, a clinical associate professor in TCD’s School of Medicine and a consultant geriatrician at TUH.

He also pointed out that nursing home residents “are frequently excluded from translational research” despite the fact that this is the population “at greatest risk of morbidity and mortality from Covid-19 illness”.

The study is published in the Journal of the American Medical Directors Association (JAMDA).