You should keep track of those who participate in clinical trials and you monitor vaccine recipients. Certain factors, such as long-term effects, cannot be fully determined without the benefit of time; you can't simulate your way out of this one. You can only hope that the size of clinical trials today will expose any significant potential side effects, but the truth is that only a very small part of humanity has received these vaccines so far. And these people are vaccinated for 6-8 months more; there is always the potential for long-term adverse effects on specific demographics.
The virus is currently affecting large numbers of people around the world. Many people end up in the hospital and many people die despite the best medical care available in the history of mankind. Many people are sick and tired of taking steps to prevent becoming infected with the virus and as a result, the number of hospitalizations is beginning to overwhelm the medical systems of many advanced countries. In the past five days, more than 1 million Americans have been infected, 10,000 have died, and more than 100,000 are currently hospitalized with COVID-19 complications; hospitals are becoming overcrowded; the medical personnel caring for COVID-19 patients (and all other patients) are at a broken point.
So you weigh the risks and benefits and at this point, we are forced to deploy these vaccines because the situation without vaccines is absolutely horrible. Vaccines are approved based on short-term effectiveness and safety data and the expectation that these short-term results will last a long time. These vaccines are given emergency FDA approval because clinical trials today show good efficacy and no significant short-term side effects. With vaccines, short-term side effects are highly predictable of possible long-term effects, so the prediction is that these vaccines will be safe for most vaccinated individuals. That being said, all vaccines (and all medical products, all any medical interventions of any kind) can produce some side effects.
This is why clinical trials exist at first; you are trying to establish a significant benefit to the patient under well-designed studies. The big difference between vaccines is that you provide medical intervention to a healthy person to prevent disease so the margin for risk / benefit assessment is narrower. Consider chemotherapy agents for cancer, which clearly pose a significant risk to the patient but still have a net benefit compared to not treating or treating something less effective.
All of these vaccines have undergone exact clinical testing and are very effective. Furthermore, you still need to keep track of what happens after the vaccination, to make sure things are still as good as 12-24 months on the road and when you start vaccinating a lot of people. Vaccine volunteers will be monitored for a full two-year cycle as part of the clinical trials they are currently involved in. For the general public, monitoring occurs through things like CDC / FDA's Vaccine Adverse Event Reporting System and the CDC's Vaccine Safety Datalink.
Meanwhile, due to the infectious SARS-CoV-2, an undeveloped individual runs a significant risk of infection and a SARS-CoV-2 infection runs a significant risk that a person will be hospitalized with severe complications.
It is likely that the rate of adverse effects for these novel vaccines is close to as high as the rate of adverse effects from viral infections. And because we do not prevent new infections, it puts us in a difficult situation of having to deploy the vaccine despite not really knowing about the possible long-term side effects, but it is unlikely to happen. Because people have to report adverse effects on VAERS, it is good that there is some level of discussion in the media and among the general public about the adverse effects of the vaccine; I hope the transparency of the discussion convinced people with significant hesitation about the SARS-CoV-2 vaccines to consider vaccination to protect themselves, their families and loved ones, and their communities.
Having a discussion about the risks versus the benefits of SARS-CoV-2 vaccination is good and healthy as long as it is in good faith. But such a discussion is not possible if you do not want to accept what is currently being witnessed in hospitals around the world. One of the challenges in having a discussion on vaccine risks versus benefits is often, people focus only on the side effects from the vaccine and forget to remember the side effects from the lack of vaccination. The pathogen and the need to get vaccinated can be easily forgotten when vaccines can be effective in reducing the incidence of infectious agents in the community.