SARS-CoV-2, Seasonal Influenza Vaccine Coadministration is Safe, Effective in Protection Against Viruses


Compared with COVID-19 vaccination alone, recent study findings show health care workers who received both a COVID-19 booster and influenza vaccinations did not have lower immune response or more frequent adverse events.

SARS-CoV-2 booster vaccinations have been found to reduce morbidity and mortality as the efficacy of the initial vaccine regimen decreases over time. The boosters are especially important for health care workers (HCWs) who frequently encounter populations who are susceptible to developing COVID-19 symptoms. Earlier in the pandemic, health care professionals had recommended that COVID-19 and seasonal influenza vaccines (SIVs) were administered separately; however, the recommendation to administer the 2 vaccines together was made to reduce the burden on health care professionals and increase the willingness to get vaccinated.

Health care worker preparing a vaccination

Image credit: arcyto |

A recent prospective study published in JAMA Network Open examined the safety and efficacy of SARS-CoV-2 booster vaccinations with SIVs. The study included 2 cohorts for 2 separate analyses: a reactogenicity analysis and an immunogenicity analysis. Reactogenicity was assessed by an electronic questionnaire sent up to 62 days after vaccination that addressed local and systemic symptoms, and immunogenicity was assessed by postvaccination anti-spike IgG titers. Participants involved in the respective analyses had received SIV and/or COVID-19 vaccines during the study period and participation in the SMC serology cohort or had received COVID-19 vaccine with or without SIV during the study’s period; participated in the SMC serology cohort; and had undergone serology tests before (up to 40 days) and after (6 to 70 days) vaccination with the COVID-19 vaccine.

Enrolled participants were HCWs who had received the Influvac Tetra (Abbott) influenza vaccine (2022/2023), the Omicron BA.4/BA.5-adapted bivalent (Pfizer/BioNTech) vaccine, or both. The reactogenicity analysis examined 588 participants who were placed in 1 of 3 different groups, COVID-19 vaccine-alone (85), influenza vaccine-alone (357), and coadministration (146). The immunogenicity analysis included 151 participants placed in either the COVID-19 vaccine group (74) or the coadministration group (77).

Study findings indicate that HCWs who received both the COVID-19 and SIV vaccinations did not have a substantially inferior immune response or more frequent adverse events (AEs) compared with COVID-19 vaccine administration alone, supporting the coadministration of these vaccines. The frequency of systemic reactions was 27.4% (95% confidence interval [CI], 18.2%-38.2%) in the COVID-19 vaccination-alone group, 12.7% (95% CI: 9.5%-16.7%) in the SIV vaccination-alone group, and 27.6% (95% CI: 20.5%-35.6%) in the coadministration group. Compared to the COVID-19 vaccine-alone group, the overall risk of systemic symptoms was lower in the SIV group (OR, 0.17; 95% CI, 0.09-0.33) and was similar in the coadministration group (OR, 0.82; 95% CI, 0.43-1.56). Postvaccination geometric mean titers (GMTs) in the coadministration group were estimated to be 0.84 (95% CI, 0.69-1.04) times lower than in the COVID-19-alone group. During the immunogenicity group’s 60-day follow-up period, none of the 151 participants had been infected with SARS-CoV-2.

Those who received SIV alone experienced the least reactogenicity, whereas COVID-19 vaccination alone caused similar reactogenicity to that of the coadministration cohort. An estimated mild decrease in anti-spike IgG titers with a point estimate of 16% and a CI not greater than 31% was examined; however, prior findings from immunogenicity studies indicate that changes in IgG titers did not greatly impact the efficacy of the vaccine, efficacy of the vaccine against substantially symptomatic disease, or the risk of a SARS-CoV-2 diagnosis.

The reasoning behind vaccinating HCWs with booster doses against COVID-19 takes the safety of their patients into account. The IgG response to vaccination does not necessarily correlate with reduced infection risk of vaccinated HCWs; however, according to the study authors, current literature has inconsistent reports regarding the immunogenicity of the coadministration of COVID-19 and SIV vaccines. Some studies had reported a significant decrease in postvaccination titers or reduced neutralization, whereas others found that the humoral response was similar between coadministration and COVID-19 vaccination alone.

According to the current study authors, the trial’s preserved humoral response and the similarities of the 2 groups’ reactogenic profiles demonstrates that the coadministration of both vaccines is an acceptable method of increasing vaccination adherence.

Limitations of this study include the lack of generalizability due to the study population’s composition of relatively healthy HCWs and the possibility of recall bias. Further, the study assessed the immunogenicity against SARS-CoV-2 but not influenza, which could potentially be impacted differently by coadministration of the 2 vaccines, according to the study authors. Additionally, time between vaccination and serological testing in the immunogenicity group had varied between patients, though adjustments in the analysis were made to take this into consideration. The investigators note that the results may not be generalizable to other COVID-19 vaccines, therefore, further studies will be necessary to determine their efficacy with SIVs.


Gonen T, Barda N, Asraf K, et al. Immunogenicity and Reactogenicity of Coadministration of COVID-19 and Influenza Vaccines. JAMA Netw Open. 2023;6(9):e2332813. doi:10.1001/jamanetworkopen.2023.32813

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