Overall, the NVX-CoV2373 vaccine (Novavax) is showing 89.8% efficacy in an ongoing, placebo-controlled phase 3 study. When the researchers gave a smaller group of 431 volunteers from the same study an influenza shot at the same time, efficacy dropped slightly to 87.5%.
“These results demonstrate the promising opportunity for concomitant vaccination, which may lead to higher vaccination rates and further protection against both viruses,” said study coauthor Raja Rajaram, MD, medical affairs lead, Europe, Middle East, and Africa at Seqirus, the company that supplied the influenza vaccines for the research.
The research was published online June 13 as a medRxiv preprint.
“With these COVID-19 vaccines, there are essentially no concurrent use studies,” Paul A. Offit, MD, told this news organization when asked to comment.
Traditionally, how a new vaccine might interact with existing vaccines is studied before the product is cleared for use. That was not the case, however, with the COVID-19 vaccines made available through expedited emergency use authorization.
The researchers found no major safety concerns associated with concomitant vaccination, Dr. Rajaram said. In addition to safety, the aim of the current study was to determine whether either vaccine changes the immunogenicity or effectiveness of the other.
“It’s a small study, but it’s certainly encouraging to know that there didn’t seem to be a big decrease in immunogenicity either way and the safety profile was similar. Not identical, but similar,” added Dr. Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia.
Some adverse events were more common in the co-administration group. For example, injection-site tenderness was reported by 70%, versus 58% for those who got the COVID-19 shot alone. The same was true for pain at the injection site, 40% versus 29%; fatigue, 28% versus 19%; and muscle pain, 28% versus 21%.
Rates of unsolicited adverse events, adverse events that required medical attention, and serious adverse events were low and well balanced between groups.
Fewer antibodies important?
Although co-administering the two vaccines did not change the immune response for the influenza vaccine, the spike protein antibody response to the COVID-19 vaccine was less robust.
Antibody titer levels at day 35 were 46,678 among people in the Novavax vaccine alone group, compared with 31,236 titers in the participants who received both vaccines.
“This impact did not seem to be clinically meaningful as vaccine efficacy appeared to be preserved,” the researchers noted.
Gregory A. Poland, MD, an internist and part of the Vaccine Research Group at Mayo Clinic in Rochester, Minn., agreed. “I highly doubt that is significant,” he said in an interview.
Dr. Rajaram said the antibody findings are “slightly surprising but not completely unexpected” because the same observation has been made in other combination vaccine studies. He added that the antibody levels “remain very high, although we do not yet know what antibody levels are required to achieve protection against COVID-19.”
The decrease could become more concerning if people start with fewer antibodies and they drop over time with normal waning of protection, Dr. Poland said. This group could include people over age 65 or people who are immunocompromised. More data would be needed to confirm this, he added.