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What we know and don't know about how well the COVID-19 vaccines work

The hope is that a COVID-19 vaccine will prevent symptoms, infection and transmission of the virus, but more research is the only way to know the true efficiency.

HOUSTON — There are 11 COVID-19 vaccine clinical trials happening right now in the United States.

Pfizer and Moderna are the furthest along. The FDA could approve Pfizer’s two-dose vaccine for emergency use next week.

Dr. Alan Barrett is the director of the Sealy Institute for Vaccine Sciences at UTMB. He says the FDA is using symptoms as the benchmark for if COVID-19 vaccines are effective.

Pfizer and Moderna have reported their vaccines are 95% effective in preventing symptoms of COVID-19.

“It’s a great story. However, these vaccines were evaluated seven days after the second dose of vaccine, so we know the vaccines elicit a really good immune response in people seven days after the second dose. We don’t know how long immunity is going to last for,” Barrett said.

He said we also don’t know if the shots prevent infection altogether or if people with the vaccine can be asymptomatic and still contagious. The hope is a COVID-19 vaccine will prevent symptoms, infection and transmission.

Barrett said the progress so far is promising, but more research is the only way to know the true efficacy of a vaccine.

Clinical trials will go on for at least a year after the first shipments of the shots go out.

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