Phizer RCT canceled April 2026- 80% of the healthy candidates had comorbidities (big increase due to Long-COVID)

Trial Site News

"Pfizer and BioNTech have halted a large U.S. clinical trial of their updated COVID-19 vaccine in healthy adults aged 50–64, citing an inability to recruit sufficient participants. The trial, designed to meet stricter requirements from the U.S. Food and Drug Administration, sought up to 30,000 participants but collapsed under low demand, stringent eligibility criteria, and declining public interest in boosters."
"The FDA’s requirement for placebo-controlled trials in relatively healthy populations created a paradox: most adults in this age group have comorbidities, disqualifying over 80% at screening."

Claude AI April 2026

Pfizer/BioNTech recently halted a large U.S. clinical trial targeting healthy adults aged 50–64, after enrollment shortfalls made it impossible to generate the post-marketing data the FDA required. The trial specifically excluded people with common chronic conditions like hypertension or diabetes — and reports emerged that more than 80% of willing participants failed pre-screening at some sites because of those exclusions.

The company confirmed the halt was due to slow enrollment, not safety concerns. A contract research organization executive involved in the trial said: "This is a very difficult population to recruit" — because finding truly healthy, comorbidity-free adults in the 50–64 age range turns out to be remarkably hard.

So the 80% figure isn't about disqualifying sick people from receiving the vaccine — it's about how hard it is to find healthy people in that age group for a trial that required no chronic conditions at all.

Has Comorbidity Prevalence Increased Post-COVID?

Yes, there's evidence of this on multiple fronts:

Pre-COVID baseline: Using 2017 BRFSS data, researchers found that 45.4% of U.S. adults reported at least one major comorbidity (cardiovascular disease, COPD, diabetes, asthma, hypertension, or cancer), rising from ~20% in ages 18–29 to over 80% in adults aged 80+.

Long COVID as a new comorbidity burden: As of early 2023, an estimated 6.9% of all U.S. adults have ever had Long COVID. Among the roughly 50% of adults who reported having had COVID-19, 13.7% reported ever experiencing Long COVID — with the 50–64 age group most affected at 17.9%. This effectively added a new layer of chronic conditions on top of the existing burden.

North America leads globally: A 2025 systematic review and meta-analysis found that the highest prevalence of comorbidity among COVID-19 patients was in North America at 75.2%, followed by Europe at 50.9%.

Top 10 Comorbidities (by prevalence and COVID severity impact)

Based on the clinical trial data and COVID mortality research:

#	Comorbidity	Notes
1	Hypertension	Highest odds ratio for COVID mortality (34.7 X); most prevalent comorbidity globally at 20–22%
2	Obesity (BMI ≥30)	Present in 35.1% of Pfizer Phase 3 trial participants — the single most common comorbidity in that cohort
3	Diabetes	Odds ratio of ~20 X for COVID mortality; present in 9–11% of COVID patients globally
4	Cardiovascular disease	Odds ratio of ~19x for COVID mortality; found in 5–9% of COVID patients
5	Chronic Kidney Disease	Odds ratio of ~12x for COVID mortality
6	COPD	Associated with a 21% increase in odds of Post-COVID Condition diagnosis in hospitalized veterans
7	Pulmonary/Lung disease	Present in 7.8% of Pfizer trial participants
8	Cancer	Consistently listed among the top risk factors for severe COVID across CDC, NIH, and trial data
9	Long COVID itself	Now a recognized chronic condition affecting millions, often overlapping with other conditions
10	Immunocompromising conditions	From March 2023–Feb 2024, immunocompromised individuals had a sevenfold increase in COVID-related hospitalizations vs. the general population

Bottom line:

The 80% pre-screening failure rate is less a sign of a new health crisis and more a reflection of how chronically ill the 50–64 American population already is — a trend that predates COVID but has been worsened by Long COVID adding new conditions on top of the existing burden. It's a striking illustration of why vitamin D deficiency (which worsens most of these conditions) is such an urgent public health issue.