Johnson & Johnson's COVID-19 vaccine made headlines in early April after six women developed extremely rare blood clots following vaccination. 
Use of the one-dose shot was paused for several weeks but lifted on April 23 after both the U.S. Food and Drug Administration and the U.S. Centers for Disease Control found the vaccine was overall safe and effective.
Despite that, doubts about the J&J vaccine, particularly in older adults, continue to linger on social media.
"The clinical trial indicates that in subjects 65 years and older, the (J&J) vaccine may be only 39% effective, and in subjects 75 years or older, the age group that comprises about 60% of all COVID-19 deaths, the vaccine may be 0% effective," claims a May 18 Facebook post by a California-based anti-vaccine group called Physicians for Informed Consent, or PIC.

The post, which includes a chart detailing these and other alleged statistics, also claims the vaccine "may not be effective" in people 60 years and older with severe risk factors for COVID-19.
PIC general counsel Greg Glaser told USA TODAY the numbers in the post and its accompanying table were largely based on the U.S. Food and Drug Administration's emergency authorization memorandum for J&J's vaccine and PIC's own compiled references.
But in reality, the numbers PIC puts forth each overstate or oversimplify data contained in the FDA's official findings.
39% is from a confidence interval
Glaser, the PIC attorney, said the group drew its figures from Table 12 of the FDA's EUA memorandum. The table presents vaccine efficacy, or VE, as percentages observed at 14 and 28 days after vaccination.
The values listed for the 65 years and older show J&J's COVID-19 vaccine is quite efficacious – 76.5% after 14 days and 68.6% after 28 days. That's actually better than the numbers for the 18 to 64 age group, which were 64.7% and 65.1%, respectively.
Because these numbers are based on a sampling of the general population – around 40,000 participants across the United States, South Africa and Latin America – 76.5% and 68.8% represent only estimates of vaccine efficacy, specifically what is called point estimate, said Dr. Angela Branche, co-director of the Vaccine and Treatment Evaluation Unit at the University of Rochester Medical Center. 
Point estimates are typically accompanied by a range of values called a confidence interval, which is where PIC gets its "39%" effectiveness. The 95% confidence interval reported by J&J means there is a 95% likelihood the actual value is between 39% and 85%. PIC references only the low end of that range and ignores the actual estimate value of 68.6%. 
"What (PIC) is reporting here is extremely misleading because you cannot interpret confidence intervals as efficacy. Efficacy is what it is – it's a point estimate," Branche told USA TODAY. 
Confidence intervals themselves only express the precision scientists are able to assign to that number but aren't used to represent vaccine efficacy, said Dr. Matthew Laurens, an infectious disease specialist and vaccine researcher at the University of Maryland School of Medicine. 
Laurens said the range of the confidence interval is a product of how many people are enrolled in the study.
"If you look at the confidence interval for the 18 to 64, it's much tighter because the numbers (of participants within that age group) are much higher. The more people we include, the more precision we have with the vaccine efficacy," he said.
Despite there being not as many older participants as younger ones, Laurens said what was especially telling about J&J's vaccine is that it performed well against other COVID-19 variants. 
"Of the three vaccines that have received emergency authorization in the United States, (J&J's vaccine) is the only one that has been tested in clinical trials in South Africa (and Brazil)," he said. "Those variants were tested by this vaccine, still protected and still showed efficacy no matter the region whether it was North America, southern Africa or Latin America."  
This consistency across geographies, age and race is far more crucial and spoke to the fact J&J's vaccine efficacy resided in the upper 60% range than the lower bounds of a confidence interval, Laurens emphasized.