COVID-19 vaccine trials are excluding older adults, one of the disease’s most vulnerable groups, according to a new paper out this week in JAMA Internal Medicine. The paper’s authors reviewed the inclusion criteria for all COVID-19 trials registered before June 1, 2020 and found that older adults are likely to be excluded from more than 50 percent of Phase 3 clinical trials investigating pharmaceutical drugs and other treatments for the novel disease as well as excluded from 100 percent of vaccine trials to prevent the condition.

In some cases, explicit age cut-offs in enrollment excluded older adults—but in others, broad secondary criteria like exclusion because of existing chronic health issues or access to technology meant that any older adult that attempted to enroll didn’t make the cut.

Failing to include older people in later-stage vaccine trials is a big problem, both for older adults themselves and for the general population, says study author Benjamin Helfand, who is an epidemiology researcher and MD/PhD candidate at the University of Massachusetts Medical School.

Helfand and other experts say that producing vaccines that aren’t tested on all major groups of people likely isn’t going to produce the level of population immunity necessary to start moving out of the pandemic. Although scientists haven’t been able to pin down the exact percent of the population that must be immune to COVID-19 to achieve herd immunity, Helfand doubts that whatever that percentage is, it is likely unreachable without a widely available vaccine. “I’m not sure that we can get there if we’re not going to include all populations,” he says.

COVID-19 vaccine and treatment trial design has been an ongoing issue. In addition to older adults, vaccine-makers have also shied away from including children and pregnant people in their trials.

“It’s really the justice aspect of this as well,” says Helfand. If safety from COVID-19 is only available to younger able-bodied adults, like those who are enrolled in Phase 1 or 2 clinical trials, people who aren’t in that group are at a huge disadvantage.

“Delaying Phase 2 vaccine clinical trials in children will delay our recovery from COVID-19,” a group of American pediatricians write in a recently-published article in the journal Clinical Infectious Diseases. “Unnecessarily prolong its impact upon children’s education, health and emotional well-being, and equitable access to opportunities for development and social success.”

Another issue is public confidence in a vaccine and perceptions of its safety. One estimate suggests that a vaccine refusal rate above 10 percent would be enough to render vaccination ineffective in containing the pandemic. “Vaccine hesitancy is a major barrier to vaccine uptake and the achievement of herd immunity, which is required to protect the most vulnerable populations,” its authors note.

A vaccine that can’t be used by children or grandparents may seem less safe, and raise the refusal rate among even able-bodied younger adults. This outcome would prolong the pandemic and its subsequent death and suffering. That’s why it’s so important to get a vaccine right the first time.