There have been some vaccines which have had unintended side effects soon after release which were later eliminated through modification including a measles vaccine released to the US in the 1960’s prior to the standardization of large-scale clinical trials and public health transparency. Some are worried that the desire for a vaccine that would “end” the covid-19 pandemic could make officials skip some important safety protocols and longitudinal studies before being made public.

Aside from simple haste, Americans have been reluctant to embrace new vaccines in the past, simply because they were so new. This was notably true in the 1950’s with the introduction of the polio vaccine, which only 60% of Americans said they were likely to accept. This trend could also apply to a Covid-19 vaccine, even if all necessary precautions were taken.