The largest COVID-19 study to date began on Monday with 30,000 volunteers from across the United States participating in a trial of a vaccine currently being developed by the National Institutes of Health in partnership with pharmaceutical company Moderna.


While the results of the trial will likely take until around the end of the year to gather, the study represents a very significant step into a new stage of the fight against COVID-19, one in which a distant, yet increasingly possible end to the pandemic is materializing.


This study follows a recent Phase 3 trial, the last stage of a clinical study, of a vaccine being developed by researchers at Oxford University. Preliminary results are positive, indicating that participants who received the drug appeared to demonstrate immunity to the virus.


Despite the progress made by these research teams, among several others, there are still many hurdles that must be overcome to develop an effective vaccine for COVID-19.


Assuming that a vaccine successfully emerges from Phase 3 clinical trials, it will require approval by the Food and Drug Administration Center for Biologics Evaluation and Research. Only an estimated 6% of vaccines are able to enter into the market after the last stage of trials.


The next issue is distribution. While it has been announced that the vaccine would be ensured for members of the population that cannot afford it, distributing it may prove challenging. The US has currently performed nearly 53 million tests, approximately 16% of the population assuming no subject received more than one test.


Scientists distinguish between efficacy, how effective a given drug is in a controlled setting, and effectiveness, how effective that drug is in a real-world context where other factors that were controlled for in the lab may come into play. For the vaccine to have real-world effectiveness, it would need to be distributed in numbers far greater than tests have been performed.


Research suggests that if the entire population took it, a vaccine with a 60% efficacy in lab trials would be effective in halting the pandemic, meaning social distance measures could safely be suspended.


Yet even assuming a successful distribution, polls indicate that a significant number of Americans would voluntarily refuse it, with figures ranging from around 25% to 45% that either would not take the vaccine or are unsure. According to the aforementioned research by Bartsch et al., the vaccine would require an 80% experimental efficacy to compensate for 25% of the population remaining untreated.


While these factors do not preclude the possibility of an end to the pandemic in the coming year, they represent difficulties that will need to be addressed moving forward.