McMaster University researchers in Hamilton

Author: Anthony Urciuoli

Published 11/16/2021 at 11:36 AM

Researchers at McMaster University in Hamilton found that some long-term care residents no longer had high levels of antibodies months after the second dose.

The authors of a study supported by the Government of Canada through the COVID-19 Immunity Task Force (CITF) say the result directly supports the government’s decisions to administer third doses – also known as boosters.

The study found that more than 97 percent of the population produced the first antibody response that is likely to protect against the virus. However, three to five months after receiving the second dose, the researchers found that antibody levels in about 20 percent of the population had dropped to the point that the antibody response might not be strong enough to provide effective protection against the virus.

“Vaccines have worked well in our nursing homes, but we need constant vigilance about how well vaccines and other measures protect vulnerable residents,” said Andrew Costa, second director of the Global Nexus Working Group on Long-Term Crisis Management in Canada. Renewal of Clinical Epidemiology and Aging and Schlegel Chair at McMaster.

“Research continues to shed light on the risks that may lie ahead.”

About 70 percent of COVID-19 deaths in Canada have occurred in long-term care or nursing homes.

“While it is clear that antibody levels fall after the second dose of the vaccine, that does not necessarily mean that a person is susceptible to the disease, as there are other factors that affect immunity. the third dose is certainly a cautious way to avoid further deaths and illnesses, ”Costa said.

The researchers also looked at immune responses to Modernan’s SpikeVax and Pfizer-BioNTech Cominarty vaccines. Although both produced good antibody levels, most residents had a stronger response to Moderna, which contains more mRNA.

“There are a few reasons why it may make sense to use SpikeVax / Moderna for third doses and for the elderly and frail people ahead. It has a higher amount of active ingredient, and sometimes this helps strengthen the aging immune system, just like the high-dose flu vaccine we give to adults.” said immunologist Dawn Bowdish, another principal investigator and department professor. in the medical field at McMaster. “A longer interval between the first and second dose may also have allowed more time for the immune response to mature.”

The study, conducted in collaboration with Schlegel Villages, the North Joseph Institute for Health Research and Health Sciences at the North Research Institute, was published this week in The Journal of the American Medical Directors Association and was based on blood samples taken from 138 residents over eight long periods of time. nursing homes throughout Ontario from March to July 2021.

“Due to their advanced age and poorer general health, the population living in long-term care homes is experiencing a faster decline in antibodies after vaccination than the younger, healthier population,” says Tim Evans, CITF director. “While the results of such CITF-funded studies support the need for a third dose of the vaccine in this population, it remains to be seen whether this will produce a sufficient long-term antibody response and thus other measures to prevent and protect infections in the elderly.”

In Ontario, booster vaccines for COVID-19 are offered to high-risk individuals. In the coming months, the county government announced its readiness to phase out booster doses to all Ontarians 12 years of age and older.

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