The group designated in Saskatchewan as Clinically Extremely Vulnerable (CEV) is a heterogenous clinical population with factors that impair their immune response to differing degrees.
Very Limited evidence is currently available to assess the immune response following vaccination is selected clinical populations; no evidence is available to assess vaccine efficacy or effectiveness in these populations. The clinical relevance of measured immune response with respect to protection from disease is still uncertain.
In considering the immune response of the CEV population, it is recommended that the absolute difference in immune response between 1 and 2 doses be considered, as it is possible some patient groups will have lowered protection regardless of vaccine strategy.
In terms of clinical subgroups:
oOrgan transplantation recipients on immunosuppressive medication: solid organ transplant recipients receiving anti-metabolite maintenance immunosuppression therapy were less likely to develop an antibody response to an mRNA vaccine, compared to those receiving other types of therapies (37% vs 63%). In a study of 242 kidney transplant recipients on immunosuppressive therapy only 10.8% became seropositive at 28 days after a single dose of mRNA vaccine.
oCancer: A study of 151 elderly patients with solid and hematological malignancies and 54 healthy controls who received one or two doses of BNT162b2 (Pfizer-BioNTech) vaccine shows approximately 39% of solid cancer patients, 13% of hematological cancer patients, and 97% of healthy controls (p<0.0001) developed anti-S IgG 21 days following a single dose vaccine. However, response in solid cancer patients increased to 95% within 2 weeks of the second dose at 21 days.
oOther immunocompromising conditions (e.g., auto-immune disorders and therapy): some level of immunity is generated with vaccination; however, what this means clinically is unknown. It seems that ensuring the dosing is properly timed around biologic therapy is important.
Azizian, A; Lee, S; Shumilak, G; Groot, G; Reeder, B; Miller, L; Howell-Spooner, B. What are the risks or benefits of extended intervals between doses of COVID-19 vaccines compared to recommended dosing in extremely vulnerable populations? 2021 Apr 20, Document no.: EOC210302 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2021. 15 p. (CEST rapid review report).
Vulnerable populations such as those experiencing homelessness are 20 times more likely to be hospitalised due to COVID-19, 10 times more likely to require intensive care for COVID-19 and 5 times more likely to die within 21 days of a positive test for COVID-19
Many organizations advocate for socially vulnerable populations to be considered priority populations due to their oftencomplex health needs and inability to fully execute best practices for infection prevention and control
Past experiences from Hepatitis vaccination (requiring 3 injections) and H1N1 pandemic influenza vaccination indicate that partnering with community organizations to provide vaccinations in shelters, community centers and other frequently accessed places along with education and access to known, trusted healthcare providers greatly increase the uptake of vaccination among socially vulnerable populations
Beyond sheltered populations experiencing homelessness, considerations for equitable vaccination programs for the general population should include plans for accessibility for all, including underserved geographic regions
Badea, A; Reeder, B; Hanson, L; Miller, L; Howell-Spooner, B. What are the vaccination strategies for vulnerable populations? 2021 Mar 12; Document no.: PH030401 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2020. 33 p. (CEST rapid review report)