Q&A with Andrew Costa: 3rd Dose and COVID-19 Immunity in Long-Term Care

November 24, 2021

In the first webinar of our Research Break series, Andrew Costa, Schlegel Research Chair in Clinical Epidemiology, discussed his study looking at COVID-19’s impact on long-term care residents, staff and visitors. He also explained the current research on the need for 3rd vaccines.

There were many excellent questions that we ran out of time for Andrew to answer them all! Below, you will find Andrew’s answers to those questions and the full recording, including the Q&A period.

On average, how many days after the third dose is the older person once again protected?

The general guidance is that it takes about two weeks for a person’s immune system to build a protective response (https://www.cdc.gov/coronavirus/2019-ncov/vaccines/keythingstoknow.html), but it should be noted that every person is a bit different and older adults may take a bit longer. We generally expect ‘peak’ antibody creation for all residents at about 3-5 weeks post-vaccination, which is the window we will be measuring our participants. It should also be noted that the 3rd dose of the original vaccine was designed for the original (Wuhan) variant. It is less effective with the circulating Delta variant but still offers substantial (but not perfect) protection, especially protection from severe infection.

Was there any analysis of commonalities amongst residents who didn’t respond as well (age, gender, comorbidities?)

The analyses are incomplete. We can say that there are no demographic factors to protection in long-term care (LTC) residents. Work is ongoing.

At what point do you expect to have data to help us understand the efficacy of third doses in people over the age of 65?

The best evidence is trial evidence, which we likely will not have outside of the trials we have that showed the efficacy and safety of the currently approved vaccines. The next best is evidence where we compare those with and without the 3rd dose, but that evidence is hard to get since the decision to offer a 3rd dose is often at the population level (everyone vs. no one) so there isn’t much to compare. Congregate living older adults that have been recommended for a 3rd dose based on good evidence that 1) 2 doses were not enough for some (a small but important number) to have an immune response at strong as other groups, 2) that their immunity wanes over time more than other groups, and 3) that they are more likely to be exposed to the virus. Since the vast majority of residents will consent to a 3rd dose based on these facts, we won’t be able to compare COVID-19 rates to those who don’t consent very effectively. Personally, I wouldn’t want me or a loved one to be left without the 3rd dose so that we can examine the benefit more accurately; that has been deemed unethical given the strong evidence for the vaccines in LTC and older adults. What we will be able to measure is their immune response to the 3rd dose, and how that immune response correlates with COVID-19 infections rates and outcomes. We will also be able to compare ourselves to other jurisdictions that don’t have the 3rd dose for LTC residents, but these jurisdictions are rare and any comparison can be fraught with error.

Based on what you have seen in the younger people and their relatively high antibody development, do you foresee a need for people under the age of 65 to be given a third dose?

Antibody development and other immune markers are being studied in many groups. When there is concern, those data are reviewed at many levels to make a consensus decision on the need for a 3rd dose. These recommendations have been made for certain groups on an ongoing basis. My own view based on the data I have seen (which I do not warrant as perfect) and the consensus of many groups, is that the data we have do not support the need for a 3rd dose on a broad scale yet. This could change over time as new data continues to come in – scientists continue to study this. That breakthrough infections happen is expected, since the original vaccine was designed for the original (Wuhan) variant and is less effective with the circulating Delta variant. In most people (with ‘normal health’) and even older people the data and consensus so far show that they remain very much protected from severe infection. This is why it is very very rare in Canada to have someone vaccinated that is hospitalized with COVID-19.

Was the response of T-cells and B-cells taken into account?

We are looking at this now. The cellular immune response is different for frail older people than younger people, and we don’t yet know how much it comes into play.

Do you have any data available yet on antibody response while considering resident-level characteristics such as gender or nutritional status?

The analyses are incomplete. We can say that there are no demographic factors on protection in LTC residents. Work is ongoing.