Story at a glance

  • As the FDA reviews vaccine data, Pfizer’s candidate has a 95 percent efficacy rate following two doses.
  • Serious, nonfatal side effects were rarely seen.

Ahead of Pfizer and BioNTech’s COVID-19 vaccine candidate being approved for emergency use by the U.S. Food and Drug Administration (FDA), new documents reveal that the vaccine maintained its high efficacy rate, even with just one dose. 

When the pharmaceutical company released its efficacy findings after clinical studies in early November, officials said that the vaccine would come in two doses. 

Now, new documents reveal that the vaccine has an 88.9 efficacy rate following just one dose. The FDA released the documents ahead of a Dec. 10 meeting between the Center for Biologics Evaluation and Research, Vaccines and the Related Biological Products Advisory Committee to discuss emergency use authorization for the vaccine.


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While just one dose of the vaccine may protect against a serious COVID-19 infection, the report authors note that the efficacy after the first dose and before the second dose “cannot support a conclusion on the efficacy of a single dose of the vaccine,” primarily because most subjects received Dose 2 after three weeks. 

The vaccine only becomes more effective after the second dose. Seven days following receiving the second dose, the vaccine efficacy rate jumped to 95 percent among individuals with no prior COVID-19 infection, and similarly 94 percent in the group containing people who previously contracted the virus.

The report also notes that efficacy percentages were “consistently robust” across more diverse demographic subgroups, holding at least a 93 percent efficacy rate.

The efficacy rate was evaluated by monitoring how many subjects who obtained the vaccine contracted the virus versus those who received a placebo.

Without the second round of vaccinations, all test individuals eventually contracted the virus. The individual who was administered the vaccine, however, did not suffer a severe illness and was not hospitalized, unlike some of their counterparts in the study.

Some of the most common side effects were non-life-threatening, including a fever, injection site pain, fatigue, headache and chills. Overall, the instance of non-fatal, serious adverse effects was low, occurring less than 0.5 percent of the time. 

The U.S. has ordered the first 100 million doses of Pfizer and BioNTech’s vaccine, spending $1.95 billion. 

This is the latest promising vaccine news to come as COVID-19 infections are rising across the country following a high volume of Thanksgiving travel, with national data showing a 16 percent increase over the last two weeks. 

Similar increases in deaths and hospitalizations — indicators of severe illness — are also rising. 

Should the Pfizer vaccine be approved for emergency use, experts say it can be ready to distribute among priority populations, namely health care workers and long-term care residents, by this Friday.

“If the FDA Commissioner decides to issue approval, the EUA, on that day when the vote is taken, as early as Friday of next week we could see vaccinations happening across the country,” James Hildreth, a member of the FDA vaccine advisory committee and the President and CEO of Meharry Medical College, said last weekend.


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Published on Dec 08, 2020