Discussion
Vaccination in oncology patients is typically limited to diseases that
are highly prevalent with high risk for morbidity and mortality. This is
largely because we know that efficacy of vaccination in
immunocompromised patients is poor.1 The analysis of
our pediatric oncology cohort, albeit small, reiterates the findings
seen in pediatric and adult oncology and transplant patients.
Specifically, our cohort showed an inadequate immune response to
SARS-COV2 vaccination compared to healthy controls. There was a notable
difference between B cell response and T cell response, with less
patients having an adequate B cell response. No patients received
targeted B cell directed therapy, but we do not have lymphocyte subset
data to quantitate B vs T lymphocytes. Another limiting factor is our
ability to only complete the T cell assay once, which may impact the
validity of that data compared to the B cell data which was repeated
multiple times. Lastly, while no patients received steroids during
within one week of SARS-COV2 vaccination, many of them had steroids in
that phase of therapy, which may have had a greater impact on T cell
immunity.12
While previous studies have demonstrated worse immune response in
patients with leukemia/lymphoma as compared to solid tumor
malignancy,4–7 our numbers were too small to detect
differences between these two cohorts. Similarly, we did not find
significant differences in immune response based on ALC or degree of
myelosuppressive therapy, suggesting that ALC or phase of therapy may
not be useful in guiding timing of vaccination or boosters.
There were two other studies to date that have also looked at immunity
after SARS-COV2 vaccination in pediatric oncology patients. Both of
these studies were from European countries, where only the BNT162b2
(Pfizer) vaccine was available. One study out of Germany included 21
pediatric oncology patients after receiving three doses (the two dose
series and a booster).4 The majority of these patients
elicited both B and T cell immunity, which was stronger in patients with
a solid tumor malignancy and in maintenance phase of therapy. The other
study by a group in the Netherlands analyzed 73 patients who received
either 2 or 3 doses and also included patients who received a
hematopoietic stem cell transplant or CAR T-cell
therapy.3 This study demonstrated that time between
last treatment and start of the vaccination series impacted immunity,
with improved vaccination response in patients who were > 6
weeks from last treatment. Similar to the German study, they showed that
three dose series was effective in increasing the humoral immune
response. There are a few key differences between these studies and
ours. First, there are differences in treatment regimens between North
America and Europe that may impact immune response during therapy.
Additionally, these other two studies did not include healthy patients
as a control, but rather used cutoffs defined by the assays to determine
response. Lastly, all of our patients only received a two vaccine
series, with very few patients receiving boosters. Our data, taken in
context of these other two studies, reiterate the value of booster shots
in immunocompromised patients.
The major limitation of our study is a small cohort size, which impacted
our ability to analyze how different clinical factors may impact
response. Similarly, our minimal enrollment of patients with solid tumor
malignancy did not allow us to assess how different malignancies may
impact response to vaccination. The Children’s Oncology Group has a
study currently open to evaluate immunologic response to COVID-19
vaccination in pediatric oncology patients. This study should shed
additional light on how immunocompromised children responds to
vaccination, what factors may impact that response, and most
importantly, how we should counsel our patients and families regarding
risks of infection, importance and timing of boosters, and risk for
serious sequelae.