Bivalent Boosters Revived Antibodies in Nursing Home Residents, 2022

Key points

• Nursing home residents' antibodies waned within months of their monovalent COVID-19 boosters, whether or not they had been infected.
• The bivalent booster — with an Omicron BA.4/BA.5 component — sharply raised antibody levels against the original (Wuhan) strain and Omicron BA.1 and BA.4/BA.5, regardless of prior infection or one versus two earlier boosters.
• Neutralizing antibodies after the bivalent dose were higher than after residents' most recent monovalent booster.
• As of January 8, 2023, only half of nursing home residents and 22% of staff had received a bivalent booster.

Why study this

Monovalent mRNA vaccines, introduced in late 2020, greatly reduced COVID-19 illness and death in nursing homes — more than 80% of residents had completed a primary series by July 2021. But their effectiveness fell during the Omicron period, leading to bivalent boosters. Older nursing home residents often respond weakly to vaccines, and how they responded to the bivalent booster was unknown.

The study

• 233 long-stay volunteers from 28 community nursing homes and veterans homes in Ohio and Rhode Island, followed since their primary series.
• Median age 74; 53% women; 79% White, 19% Black, 1% Hispanic.
• All completed a primary series by February 2021 and a first booster within nine months; 78% had a second monovalent booster. All received the bivalent booster in September–November 2022.
• About 77% had a previous infection. People infected between their last booster and the bivalent dose were excluded.
• Blood was tested for anti-spike (binding) and neutralizing antibodies against Wuhan, BA.1 and BA.4/BA.5 at three points: about 2 weeks after the last monovalent booster, just before the bivalent booster, and about 2 weeks after it.

Results

• Before the bivalent dose, both kinds of antibodies had declined substantially (statistically significant in every case except BA.5 neutralization after only one earlier booster).
• After the bivalent dose, every measure rose substantially from the pre-bivalent level (all p < 0.001), restoring immunity that had waned.
• Neutralizing antibodies against Wuhan, BA.1 and BA.4/BA.5 rose above the levels reached after the most recent monovalent booster.
• Binding antibodies against Wuhan and BA.1 rose but did not exceed post-monovalent levels.
• Prior infection did not change the response; two earlier boosters gave a higher anti-spike BA.1 response than one.

Neutralizing antibody levels (pseudovirus assay) against Wuhan, BA.1 and BA.4/BA.5, in residents with one (left) or two (right) earlier monovalent boosters, before and after the bivalent booster. CDC.

Anti-spike binding antibody levels at the same time points. CDC.

What it means

The bivalent booster broadens and strengthens nursing home residents' immune response to Omicron, supporting the recommendation that residents — and staff, whose vaccination also protects residents — get it. At the time, CDC advised residents to get a bivalent booster if at least 2 months had passed since their last dose.

Limitations

• Antibody levels do not translate directly into protection for an individual.
• Some undetected infections may have boosted antibodies and been mistaken for a vaccine effect.
• The sample was small and included more men than typical, because of two veterans homes (earlier studies found no sex difference in response).
• Some participants had missing time points.

Sources

Based on David H. Canaday, Oladayo A. Oyebanji, Elizabeth M. White et al., "SARS-CoV-2 Antibody Responses to the Ancestral SARS-CoV-2 Strain and Omicron BA.1 and BA.4/BA.5 Variants in Nursing Home Residents After Receipt of Bivalent COVID-19 Vaccine — Ohio and Rhode Island, September–November 2022," Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention, by authors from Case Western Reserve University, Brown University, the Ragon Institute, CDC and other institutions; published by CDC.