COVID-19 vaccines
Vaccines typically require years of research and testing before reaching the clinic, but this year researchers embarked on a global effort to develop safe and effective coronavirus vaccines in record time. Both the Pfizer/BioNTech and Moderna vaccines have only a few months of phase 3 clinical trial data, so much remains unknown about them, including their duration of effect and any long-term safety signals. In addition to excluding immunocompromised individuals, the clinical trials did not include children or pregnant women, so data are lacking for several population subgroups.
But these will not be the only vaccines available, as the pipeline is already becoming crowded. U.S. clinical trial data from a vaccine jointly being developed by Oxford-AstraZeneca, could potentially be ready, along with a request for FDA emergency use authorization, by late January 2021.
In addition, China and Russia have released vaccines, and there are currently 61 vaccines being investigated in clinical trials and at least 85 preclinical products under active investigation.
The vaccine candidates are using both conventional and novel mechanisms of action to elicit an immune response in patients. Conventional methods include attenuated inactivated (killed) virus and recombinant viral protein vaccines to develop immunity. Novel approaches include replication-deficient, adenovirus vector-based vaccines that contain the viral protein, and mRNA-based vaccines, such as the Pfizer and Moderna vaccines, that encode for a SARS-CoV-2 spike protein.
“The special vaccine concern for immunocompromised individuals is introduction of a live virus,” Dr. Stohl said. “Neither the Moderna nor Pfizer vaccines are live viruses, so there should be no special contraindication for such individuals.”
Live vaccine should be avoided in immunocompromised patients, and currently, live SARS-CoV-2 vaccines are only being developed in India and Turkey.
It is not unusual for vaccine trials to begin with cohorts that exclude participants with various health conditions, including those who are immunocompromised. These groups are generally then evaluated in phase 4 trials, or postmarketing surveillance. While the precise number of immunosuppressed adults in the United States is not known, the numbers are believed to be rising because of increased life expectancy among immunosuppressed adults as a result of advances in treatment and new and wider indications for therapies that can affect the immune system.
According to data from the 2013 National Health Interview Survey, an estimated 2.7% of U.S. adults are immunosuppressed. This population covers a broad array of health conditions and medical specialties; people living with inflammatory or autoimmune conditions, such as inflammatory rheumatic diseases (rheumatoid arthritis, axial spondyloarthritis, lupus); inflammatory bowel disease (Crohn’s disease and ulcerative colitis); psoriasis; multiple sclerosis; organ transplant recipients; patients undergoing chemotherapy; and life-long immunosuppression attributable to HIV infection.
As the vaccines begin to roll out and become available, how should clinicians advise their patients, in the absence of any clinical trial data?
Risk vs. benefit
Gilaad Kaplan, MD, MPH, a gastroenterologist and professor of medicine at the University of Calgary (Alta.), noted that the inflammatory bowel disease (IBD) community has dealt with tremendous anxiety during the pandemic because many are immunocompromised because of the medications they use to treat their disease.