Usually, vaccine testing and production are done in multiple, time-consuming, separate steps over several years. Because of the pandemic, the federal government provided special funding to vaccine researchers and manufacturers to allow development, testing and production to happen at the same time. No steps are skipped but the timeline for development can go faster.
Vaccines that have been authorized from Pfizer and Moderna are mRNA vaccines. mRNA vaccine technology has been studied and worked with for decades. Interest has grown in these vaccines because they can be developed in a laboratory using readily available materials. This means the process can be standardized and scaled up, making vaccine development faster than traditional methods of making vaccines.
The Johnson & Johnson vaccine is a viral vector vaccine, a technology first created in the 1970s. For decades, hundreds of scientific studies of viral vector vaccines have been done around the world. They have been used against other infectious diseases like Ebola, Zika, flu and HIV.
When a vaccine is authorized by EUA, volunteers who get the COVID-19 vaccine are monitored for a shorter time than with the traditional vaccine approval process. Testing for any COVID-19 vaccine involves thousands of volunteers, and at least half of the volunteers are followed for at least 2 months after their last vaccine dose (rather than the 6 or more months in a traditional process). However, by two months, most side effects from vaccines are expected to surface.
It is possible that rare side effects may only be seen when millions of people are vaccinated. For this reason, the safety of COVID-19 vaccines will continue to be monitored after they are given.