Vaccine Distribution & Scheduling

Full approval by the U.S. Food & Drug Administration grants a license to vaccine manufacturers. This means they can market their product in the United States for use in the population for which it is approved.

Until now, COVID-19 vaccines were distributed in the United States under emergency use authorization (EUA). These were issued after clinical trials tracked results for tens of thousands of volunteers for at least two months. EUA is a way to speed delivery of safe and effective medicines during public health emergencies, such as the COVID-19 pandemic.

Full approval, such as that issued for ages 16 and older for the vaccine by Pfizer-BioNTech, takes a longer review. The original tens of thousands of clinical trial participants are monitored for at least six months. In addition, regulators review any reports of adverse reactions among the hundreds of millions of doses given in the United States. Vaccine manufacturers also must submit much more detailed documentation.

Read a step-by-step explanation of the vaccine development process.

The authorized vaccines continue to provide very strong protection, particularly against severe illness, hospitalization and death.

However, health officials cite two reasons for the need for a booster: Evidence shows vaccine-induced protection against COVID-19 infection begins to decrease over time, which also occurs with a natural infection. And the vaccine effectiveness is generally not as strong against the Delta variant. Boosting the previous vaccine series should provide more protection against the Delta variant and probably other variants, too.

In fact, many vaccines require multiple doses – the polio vaccine and the diphtheria-tetanus vaccine are just a couple of common examples.

Variants are common with every virus – think of the season flu as an example. Every time a virus reproduces, there is a chance for a genetic copying “error” or mutation.

Mutation and evolution often result in a virus that spreads more easily, which is what appears to have happened with the highly contagious Delta variant. Studies also suggest that this variant, which has become dominant in many parts of the country, including Michigan, causes more severe illness.

This is why it is so important to reduce infections through vaccination and other precautions. Every time the virus is passed on is another opportunity to mutate.

The primary concern is for unvaccinated people. However, no vaccine is 100% effective.

The COVID-19 vaccines authorized for use in the United States (the vaccine by Pfizer-BioNTech now is fully licensed for ages 16 and older) continue to show strong protection in preventing severe disease, hospitalization and death. This includes illness caused by the Delta variant.

However, the Delta variant is not only more contagious, but may cause more severe illness than earlier strains.

Studies also show that it is possible for fully vaccinated people to experience rare “breakthrough” infections and spread the virus to others.

For these reasons, the CDC is recommending layered prevention strategies, such as wearing masks in public settings.