Efficacy of the NVX-CoV2373 COVID-19 Vaccine Co-Administered With Seasonal Influenza Vaccines

Influenza vaccine
Influenza vaccine
Researchers conducted a study to assess the efficacy of the NVX-CoV2373 COVID-19 vaccine when co-administered with a seasonal influenza vaccine.

Concomitant administration of the NVX-CoV2373 COVID-19 vaccine and a licensed seasonal influenza vaccine may be a viable immunization strategy, according to study results published in The Lancet Respiratory Medicine.  

In this exploratory sub-study of a phase 3 trial conducted at 4 hospitals in the United Kingdom, investigators assessed the safety and efficacy of the NVX-CoV2373 COVID-19 vaccine when co-administered with seasonal influenza vaccine. Participants eligible for the sub-study included those who met the inclusion criteria for the initial phase 3 trial and had no contraindications to influenza vaccination. Participants were randomly assigned in a 1:1 fashion to receive either the NVX-CoV2373 vaccine plus the influenza vaccine or placebo plus the influenza vaccine. Although participants in the initial phase 3 trial were blinded, the investigators noted that those included in the sub-study received the influenza vaccine in an open-label manner.

In addition to evaluating the reactogenicity for a period of 7 days following vaccination, the investigators assessed the occurrence of unsolicited, medically attended, and severe adverse events among the included participants. They also assessed immunogenicity via influenza hemagglutination inhibition and SARS-CoV-2 anti-spike protein immunoglobulin G assays. Comparisons were made between participants in the main and sub-studies, and the trial was registered at ClinicalTrials.gov (number NCT04583995).

A total of 431 participants were included in the sub-study and were co-vaccinated with a licensed seasonal influenza vaccine. Of these participants, 217 concomitantly received the NVX-CoV2373 vaccine and 214 concomitantly received placebo. Of note, participants included in the sub-study tended to be younger, more racially diverse, and had fewer comorbidities compared with those included in the initial phase 3 trial. Compared with participants who received the NVX-CoV2373 vaccine alone, reactogenicity events were increased among those who received both the NVX-CoV2373 and influenza vaccines. Reactogenicity events between participants who received both the COVID-19 and influenza vaccines vs those who received the COVID-19 alone included tenderness (64.9% vs 53.3%) or pain (39.7% vs 29.3%) at the injection site, fatigue (27.7% vs 19.4%), and muscle pain (28.3% vs 21.4%).

Among participants in both treatment groups, the incidence of unsolicited, medically attended, and severe adverse events was decreased. In addition, there were no reports of anaphylaxis or death among participants included in the sub-study. Although no changes in immune response to the influenza vaccine occurred due to co-vaccination, the investigators noted that the antibody response to the NVX-CoV2373 vaccine was decreased. Among participants included in the initial phase 3 trial and those included in the sub-study, the efficacy of the NVX-CoV2373 vaccine was 87.5% (95% CI, -0.2 to 98.4) and 89.8% (95% CI, 79.7-95.5), respectively.

Study limitations included its small sample size and number of efficacy endpoints. In addition, no formal prespecified noninferiority statistical assessment of immunogenicity was performed, and randomization did not occur for participants included in the sub-study.

According to the investigators, “these data show no early safety concerns with the concomitant administration of NVX-CoV2373 with an influenza vaccine.” They concluded that “future clinical trials and postlicensure studies of COVID-19 vaccines should include safety and immunogenicity data for co-administration with common adult and pediatric vaccines, [and] more research on the concomitant vaccination of COVID-19 and influenza vaccines is needed, especially in those older than 65 years, to help guide national immunization policy on this important issue.”

Disclosure: This research was supported by Novavax. Please see the original reference for a full list of disclosures.


Tobak S, Galiza E, Cosgrove C, et al. Safety, immunogenicity, and efficacy of a COVID-19 vaccine (NVX-CoV2373) co-administered with seasonal influenza vaccines: an exploratory substudy of a randomised, observer-blinded, placebo-controlled, phase 3 trial. Lancet Respir Med. Published online November 17, 2021. doi: 10.1016/S2213-2600(21)00409-4