A recent article in the journal The Lancet (Haematology), one of the pre-eminent medical journals in the world, opens with the following wake-up call:
“The prognosis of COVID-19 infection is poor in hematopoietic stem cell transplant (HSCT) recipients. In a large multicentric series of 318 HSCT recipients (184 allogeneic HSCT recipients and 134 autologous HSCT recipients), the probability of overall survival at 30 days after the diagnosis of COVID-19 infection was notably dismal, at 68% and 67% for allogeneic HSCT recipients and autologous HSCT recipients, respectively.”
The article then continues with a reminder that immunecompromised patients were excluded from participating in the early trials of this vaccine (and others). Therefore, there is a need to understand the efficacy of the mRNA vaccines in this population.
A team of researchers at the Hôpital Henri Mondor (France) followed a total of 88 patients, who had received 2 successive doses of the Pfizer vaccine, 4 weeks apart as required by the manufacturer. Spike glycoprotein-specific IgG was quantified for each patient at a median time period of 28 days after the second vaccine dose and a median 23-month period after their allo-stem cell transplant.
The question then arises, what level of protection is conferred on those patients whose titers can be quantified? Let me pause here for a minute and talk a bit about antibody titer tests. There are several tests on the market that report outcomes on different scales. This makes it hard to compare one set of test results to another, without knowing what test and what test equipment were used. In this case, the authors of the report used the IgG II Quant Assay (Abbot Laboratories, Wiesbaden, Germany) to quantify spike glycoprotein-specific IgG receptor-binding domain (IgG[S-RBD]). It has been previously reported that the surrogate measure of 4,160 Arbitrary Units per milliliter (AU/mL) corresponds with a 95% probability of Covid virus neutralization. As such, this titer level (for this specific test) has been chosen as a measure that confers a high protection against Covid in this study (as well as others that rely on the same testing methods).
“Our findings support the large-scale vaccination of allogeneic HSCT recipients, although additional multi-center and long-term studies are needed to specify the level of immunological protection against infection, also taking into account the effect of a third vaccine dose in non-responding patients.”
And I interpret this statement as saying that, as of yet, we really do not know yet what the level of antibody titers is that will give a high degree of confidence of protection (is it the 4,160 mentioned above or is something different?) AND we are setting the stage that booster shots may/will be needed for immuno-compromised patients such as we, folks with AML, are.
about the author
I was diagnosed in 2014 with blood cancer and have been very fortunate to find treatment at the division of Cellular Therapy at the Duke University Cancer Institute. My wife, Vicki, and I have two adult children and a grandson who is the ‘light of my life’. Successful treatment has allowed Vicki and I to do what we love best: traveling the world, albeit it with some extra precautions to keep infections away. My career in the pharmaceutical industry has given me insights that I am currently putting to use as an advocate to lower drug pricing, especially prices for anti-cancer drugs and, very specifically, CAR-T therapies, with recent contributions posted by Health Affairs, the Institute for Clinical and Economic Review and the Centers for Medicare and Medicaid Services.