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A large-scale “real-world” test of Pfizer’s Coronavirus vaccine found that it’s very effective at preventing serious illness or death, even after one dose.

The discovery published on Wednesday says the vaccine gave strong reassurance in half a million people tested to the smaller, limited test prior to emergency authorization use. The vaccine was used widely in a general population with various ages and health conditions to get a broad scope of the vaccine’s effectiveness.

The Pfizer vaccine was 92% effective at preventing severe disease after two shots, and 62% after one. It rivals Johnson & Johnson’s one-shot variety of the vaccine which is said to be 66% effective at preventing the virus and its complications.  What makes Pfizer’s unique is the effectiveness for preventing death was 72% two-or-three weeks after the first shot, a rate that may improve as immunity builds over time.

The people who were tested above the age of 70 were protected similar to those in the younger groups too.

Two doctors were amazed at the results of the test. “This is immensely reassuring … better than I would have guessed,” Mayo Clinic’s Dr. Gregory Poland told AP News.

Vanderbilt University’s Dr. Buddy Creech agreed with the assessment saying, “Even after one dose we can see very high effectiveness in prevention of death,” he said.

There were 41 COVID-19-related deaths, 32 of them in people who did not get a vaccine.

Overall, the numbers compare well to the 95% effectiveness after two doses that was seen in the limited testing that led U.S. regulators to authorize the vaccine’s emergency use, Poland said. How much benefit there would be from one dose has been a big question, “and now there’s some data” to help inform the debate, he added.

“Maybe the right thing to do here to protect the most number of people … is to give everybody one dose as soon as you can. I think that’s a very acceptable strategy to consider,” Poland said.

As of Wednesday, 19.8 million people were fully vaccinated in the U.S., and a total of 43.6 million worldwide– a little over a half of a percent of the global population.

Pfizer COVID-19 vaccine passes big ‘real world’ test  was originally published on