A single dose of the Pfizer-BioNTech vaccine for people who have already had COVID-19 generates an immunologic response similar to that in people who receive the two-dose recommended sequence, according to a study released Thursday by researchers at Cedars-Sinai.
The study suggests that the second dose may not be needed for people who have successfully recovered from a prior coronavirus infection, according to Dr. Susan Cheng, an associate professor of cardiology and director of Public Health Research at the Smidt Heart Institute at Cedars-Sinai.
“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,” Cheng said. “This approach could maximize the reach of a limited vaccine supply, allowing potentially millions more people to be vaccinated in the U.S. alone.”
The Pfizer vaccine is normally administered in two doses 21 days apart.
“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,” said Kimia Sobhani, medical director of the clinical core laboratories and 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.”
Just under 1,100 health care workers in the Cedars-Sinai Health System who received the Pfizer vaccine were surveyed about prior coronavirus infections and any symptoms they might have experienced after being vaccinated. Researchers identified 35 people with prior coronavirus infections who had received a single vaccine dose and 228 individuals without prior infection who had received both vaccine doses, and found that antibody tests showed levels and responses of coronavirus-specific antibodies were similar in both of these groups.
Post-vaccine symptoms were more prominent after the first dose for those with prior infection, but symptomatology was similar between the two groups after the second dose, the researchers said. Investigators said their study had limitations and that more research will be needed to confidently guide vaccine policy.
Researchers noted that they measured antibody levels only up to 21 days after each vaccine dose and that longer-term follow-up likely would provide additionally informative data, especially regarding the duration of the immunity acquired from receiving a single versus double dose of the vaccine, and that even larger cohort samples will be needed to examine differences across demographic and clinical subgroups that are known to exhibit variation in antibody response following vaccination.
More studies also are needed to determine if the results seen after a single dose of the Pfizer vaccine might also apply to other SARS-CoV-2 vaccines, the researchers added. The vaccine study and related research are part of the Coronavirus Risk Associations and Longitudinal Evaluation study conducted by a network of clinicians and scientists from multiple institutions, primarily in Southern California.