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"Our findings extend those from smaller studies reported elsewhere and support a potential strategy of providing a single dose of vaccine to persons with a confirmed prior history of coronavirus infection, along with two doses for people not previously infected," said researcher Dr. Susan Cheng. She's an associate professor of cardiology and director of public health research at the Smidt Heart Institute at Cedars-Sinai Health System, in Los Angeles.
"This approach could maximize the reach of a limited vaccine supply, allowing potentially millions more people to be vaccinated in the U.S. alone," Cheng said in a health system news release.
For the study, Cheng and her colleagues assessed almost 1,100 health care workers in the Cedars-Sinai system who had received at least one dose of the two-dose Pfizer/BioNTech vaccine. Antibody tests measured their immune system's response to the vaccine.
The participants' antibody response was checked three times: before or up to three days after the first dose; within seven to 21 days after the first dose; and within seven to 21 days after the second dose.
Based on surveys completed by the health care workers, the researchers identified 35 with prior coronavirus infections who had received a single dose of the vaccine and 228 who had not been infected and had received both vaccine doses.
The antibody tests showed that both of those groups had similar levels and responses of coronavirus-specific antibodies, according to the study. The results were published online April 1 in the journal Nature Medicine.
According to co-senior author Kimia Sobhani, "Overall, individuals who had recovered from COVID-19 developed an antibody response after a single vaccine dose that was comparable to that seen after a two-dose vaccination course administered to individuals without prior infections." Sobhani is an associate professor of pathology and laboratory medicine at Cedars-Sinai.
"It appears that a single booster dose given to previously infected individuals offers the same benefit as two doses given to people without prior infection," Sobhani added.
Further research is needed to help guide COVID-19 vaccination policy, the study authors said.
The researchers noted they measured antibody levels only up to 21 days after each vaccine dose, and said longer-term follow-up is likely to provide better information, especially about the length of immunity provided by a single dose compared to both doses of the vaccine.
SOURCE: Cedars-Sinai, news release, April 1, 2021
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