The reason why vaccinated people need a booster shot

It sounds confusing federal health officials say the Covid-19 vaccines are working well, providing more than 90% protection against severe disease and death. They're keeping people away from the hospitals. Yet some studies show even fully vaccinated people are in danger.

This is where some of the debate over the need for boosters comes in. The World Health Organization and some infectious diseases experts note that the vaccines are still doing their most important job—preventing severe disease and death.

"The third dose will likely do very little for further boosting the vaccine's ability to reduce hospitalizations and deaths. That's because the vaccine is already pretty darn good at that," Hensley said.

So health officials, doctors and nurses across the country are clamoring for more Americans to get vaccinated and WHO is pushing for more vaccines to be distributed to the rest of the world.

One study of nursing home residents showed immunity from any kind of infection fell from 75% in March to 53% in August. So this makes clear that protection against mild and moderate disease has decreased over time and higher level of antibodies is required to protect us against the Delta.

So long as people are becoming infected with coronavirus and spreading it, the virus will infect some vaccinated people. And it will evolve into new forms, perhaps versions that can more easily evade the vaccines. 

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