“These findings could have profound significance if the protection afforded by vaccination among older adults is stronger than that of young adults because older adults are a very important target population for which we are targeting for protection with vaccination,” Chen says.
The purpose of the first phase was to assess safety and determine the most effective dose. Side effects seen in the first study included fatigue, chills, headache, muscle soreness, and pain at the site of the shot.
No placebo shots were given. Instead, recipients received two doses of either 25 micrograms or 100 micrograms given 4 weeks apart. The higher dose generated more antibodies in both groups. It also generated more side effects, including swelling and muscle soreness that lasted several days in some participants.
About 4 weeks after the 25-microgram shots, younger participants made an average antibody concentration of 323,945, while those ages 71 and up made an average concentration of 1,128,391 antibodies. After the 100-microgram shots, those ages 56-70 made an average concentration of 1,183,066 antibodies, compared to 3,638,522 in the older group.
The antibody responses measured in the study don’t necessarily mean that people are protected from infection. Researchers won’t know whether vaccination is protective until the end of the phase III trial, which is underway. But they are an encouraging sign.
“We were happy to see that the 100-microgram dose generated similar antibodies to those observed in 18- to 55-year-old recipients of the vaccine,” says Evan Anderson, MD, an associate professor of pediatric infectious disease at Emory University School of Medicine. The results from the younger adults were reported in an earlier study.
It’s not clear why this vaccine appears to generate such strong antibody responses, even among the elderly. “We don’t understand exactly why these immune responses in the older adults were still robust,” he says.
The study authors write that the antibody responses seen after the second dose of the vaccine are similar to those observed in patients who had recovered from COVID-19 and who had donated their blood for convalescent plasma. But they also note that right now, we don’t have a reliable biomarker that can tell us when someone is adequately protected against the virus.
The results were published today in TheNew England Journal of Medicine.