New York, Sep 3 (IANS): Antibodies produced by the Pfizer vaccine against Covid-19 decreased more than 80 per cent after six months in some elderly people, according to a study that emphasises the need for booster shots.

Researchers from the Universities of Case Western Reserve, Brown and Harvard studied blood samples of 120 Ohio nursing home residents and 92 health care workers.

In particular, they looked at humoral immunity, also called antibody-mediated immunity, to measure the body's defenses against the coronavirus.

The findings, published on online preprint medRxiv and being peer-reviewed, showed that individuals' antibody levels decreased more than 80 per cent after six months; the results were the same in older adults (median age 76) and caregivers (median age 48) and old alike.

The results support the Centers for Disease Control and Prevention (CDC) recommendation for booster shots, especially for the elderly, due to fading immunity, David Canaday, professor at the School of Medicine at Case Reserve.

He added that boosters are even more important as the Delta variant spreads.

The team also presented their unpublished results directly to CDC and were urged to get the data out in the public domain as soon as possible "so we could enter conversation and the decision-making process for booster vaccine recommendations", Canaday said.

The sharp decline is particularly problematic for the elderly because previous research by Case Reserve showed that within two weeks of receiving the second dose of vaccine and being considered "fully vaccinated", older adults who had not previously contracted Covid-19 already showed a reduced response in antibodies that was substantially lower than the younger caregivers experienced.

By six months after vaccination, the blood of 70 per cent of these nursing home residents had "very poor ability to neutralise the coronavirus infection in laboratory experiments", Canaday said.