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Q: How do we know that the new Pfizer vaccine is safe?

Last week, the FDA formally granted an emergency use authorization (EUA) for Pfizer-BioNTech’s coronavirus vaccine candidate which means that they reviewed and evaluated the vaccine’s risks and benefits (as they do with all vaccines) and granted the EUA based on the need to use the vaccine to quickly save lives during an urgent health crisis.
Many people are anxious about the speed with which a vaccine has been approved. While the EUA is a shorter process, no steps are skipped in the safety evaluation process. Safety is the most important requirement for the vaccine and is assessed in trials by independent experts.

It is important to point out that the approval of a vaccine for use in people involves multiple phases with different goals for assessing effectiveness and safety in different populations. There are four distinct phases, and the vaccine must meet very intense safety criteria before completing each phase. Once a vaccine is approved for use after phase 3, it has been tested in tens of thousands of people and if no significant harmful side effects are noted, it is considered safe for use. Phase 4 involves continued monitoring and gathering of safety data. This type of clinical trial has been used for decades to approve medications and vaccines.

For Phase 3 test trials, the FDA advises a minimum of 3,000 participants to assess safety. The current phase 3 trials of various COVID-19 vaccine candidates have 30,000 to 50,000 participants. The Pfizer vaccine had 44,000 people participate in their clinical trials. That also gives us confidence. Such a large trial is more likely to detect safety problems, even rare ones. It also means the vaccine has been tested in a diverse group of people.

The results so far are encouraging. Current data from drug companies Pfizer (and now also Moderna) show that their COVID-19 vaccines have an efficacy rate of 94-95%. The Federal Drug Administration (FDA) requires 50% efficacy of a COVID-19 vaccine. By comparison, in some years, the flu vaccine is only 40% to 60% effective at preventing influenza. If the COVID vaccine does turn out to be as effective as it appears, it will be in the same league as our most effective vaccines, like the measles vaccine.

One of the main challenges with the Pfizer vaccine is that it is more difficult to transport. It needs to be stored and shipped at extremely cold temperatures. That means our state and our island hospitals need to have special equipment and processes in place to distribute it, and it may make it more challenging to get the vaccine to the people in more rural areas, or islands like Lanai, to people who need it.

Maui Health is fortunate to have received an ultra-low temperature freezer from UH Maui College that can store more than enough vaccines for our hospitals, and we are prepared to receive the Pfizer vaccine any day now. We are also committed to ensuring that our hospital and community on Lanai is taken care of, and those that need the vaccine during this first stage of vaccinations, will get one.

For more information on how Maui Health is preparing to receive and administer the COVID-19 vaccine, visit For more information about vaccine safety, visit

Chrissy Miller
Employee Health Manager, Maui Health