In a pre-print, not yet peer reviewed, study led by CITF-funded researchers Drs. Andrew Costa and Dawn Bowdish at McMaster University, people in retirement or nursing homes had repeat blood samples taken to measure immunity after the second and third doses of SARS-COV-2 mRNA vaccines. Researchers found that the third vaccine dose brought about levels of neutralization capacity that were much higher than what was achieved post-second dose.

Key findings:

  • Higher neutralization capacity was achieved after a third booster dose, compared to the second dose.
  • All residents had neutralization capacity against the Beta variant following the third dose, whereas 20.8% had no detectable neutralization capacity after the second dose.
  • Beta variant neutralization was lower compared to the capacity to neutralize the wild type variant.
  • There were no differences in median neutralization titers between nursing home residents and retirement home residents 12 to 77 days following the dose.

This study was carried out in both nursing homes and retirement homes. For assessment of immunity after the second dose of vaccine.  A total of 418 nursing home residents were recruited, with an average age of 82 years, of whom 63.5% were women. The time between the second dose spanned from 12 to 240 days, with a near equal distribution between Moderna-Moderna (52.9%) and Pfizer-Pfizer (46.4%) series.

For assessment of the third vaccine dose, a total of 103 nursing home residents, together with 95 assisted living residents were recruited 12-77 days post-third dose. Both groups had an average age above 80, and the majority were women (63% and 65%, respectively). Nursing home residents received vaccines in the following order: Moderna-Moderna-Moderna (66.0%), Pfizer-Pfizer-Moderna (17.5%), or Pfizer-Pfizer-Pfizer (16.5%); whereas assisted living residents received Pfizer-Pfizer-Pfizer (61.1%), Moderna-Moderna-Moderna (22.1%), Pfizer-Pfizer-Moderna (14.7%), or Moderna-Moderna-Pfizer (2.1%).

Overall, these findings support the need for third vaccine doses in people living in nursing and retirement homes. Information regarding the neutralization capacity of boosters against Omicron in this population has not yet been assessed. Thus, continued monitoring is needed.

Zhang A, Breznik JA, Clare R, Nazy I, Miller MS, Bowdish DME, Costa AP, COVID-in-LTC Study Group. Antibody Responses to 3rd Dose mRNA Vaccines in Nursing Home and Assisted Living Residents. MedRxiv, December 2021. doi: https://doi.org/10.1101/2021.12.17.21267996