Same-Day COVID-19 and Flu Vaccination Does Not Raise Adverse Event Risk, Large VA Study Finds

Pharmacists who administer COVID-19 and influenza vaccines during the same visit now have a substantial new evidence base behind that practice. A target trial emulation published in Annals of Internal Medicine found that same-day coadministration of the 2 vaccines was not associated with a higher risk of serious or clinically meaningful adverse events (AEs) compared with influenza vaccination alone.^1,2

Researchers at Washington University in St. Louis analyzed data from more than 2.5 million patients in the US Department of Veterans Affairs (VA) health system collected between September 1, 2022, and August 26, 2025. The cohort included more than 705,000 individuals who received both vaccines during the same visit and over 1.8 million who received only the influenza vaccine.^1,2

Methodology and Findings

The study used a target trial emulation framework with an active-comparator design and inverse probability weighting, an approach intended to reduce "healthy vaccinee bias"—the tendency for healthier, more health-engaged patients to seek out vaccination—which can skew safety comparisons. Influenza-only recipients were censored from the analysis once they later received a COVID-19 vaccine, keeping the comparison groups as clean as possible. Investigators tracked 90-day risk across 46 prespecified AEs, grouped into 3 severity tiers, spanning cardiovascular and thrombotic events, neurological disorders, and other clinically significant outcomes.³

The composite results were notably consistent, with tier 1 events showing a relative risk of 1.03 (95% CI, 0.99-1.09), tier 2 a relative risk of 0.99 (0.96–1.03), and tier 3 a relative risk of 0.99 (95% CI, 0.96-1.02). Of the 46 individual AEs examined, only 2—syncope and tinnitus—reached statistical significance, and their effect estimates moved in opposite directions, which investigators noted is more consistent with chance findings than a true safety signal. Negative outcome controls, used to check for hidden bias in the data, were also consistent with an absence of measurable confounding.³

Consistency Across Vaccine Formulations

One of the study's more notable features is that it spanned 3 distinct, variant-updated COVID-19 vaccine formulations, including bivalent, XBB-adapted, and KP-adapted. Safety outcomes held steady across all 3 periods, an important finding given how frequently COVID-19 vaccine composition has changed since 2022.¹

Study author Ziyad Al-Aly, MD, professor of medicine at Washington University in St. Louis, said in an interview with Pharmacy Times that consistency was one of the more reassuring elements of the analysis. "Across the bivalent, XBB-adapted, and KP-adapted periods, we saw no significant increase in risk of AEs," he said. "That trend is reassuring, but I'd be cautious extrapolating to formulations we haven't studied. Broadly, the data support the safety of coadministering these vaccines, and I’d want continued surveillance and monitoring of each new formulation as it's rolled out."

What It Means at the Counter

For pharmacists, the findings reinforce existing CDC guidance, which has long held that COVID-19 and influenza vaccines can be given during the same visit with no required waiting period between them. But Al-Aly cautioned against treating same-day dosing as an automatic default over spacing doses apart, since that specific comparison fell outside the study's design.

"We didn't compare same-day dosing against spacing the shots apart, so I'd stop short of calling it a default recommendation on the basis of our data," Al-Aly said. "What our results do show is that same-day coadministration wasn't associated with an increased risk of serious or clinically significant AEs, which supports the safety of current coadministration practice. And from a practical and logistics standpoint, getting both vaccines in one visit makes sense for a lot of patients."

A Note on Generalizability

Because the cohort was drawn from the VA system, the population skewed older, predominantly White, and male—a limitation the study authors acknowledged.³ Al-Aly pushed back gently on concerns that this narrows the findings' relevance. "While the data is from the VA, we included more than 2.5 million individuals in the cohort, representing both sexes and a range of ages," he said. "Even though the majority were men, the numbers outside that majority were still substantial—more than 185,000 women, across a wide age range."

Fitting Into the Broader Evidence Base

The findings also align with a growing body of independent research. A systematic review published in the New England Journal of Medicine, conducted ahead of the 2025 to 2026 respiratory virus season, screened more than 17,000 references and identified 511 qualifying studies, including 17 specifically on COVID-19 and influenza vaccine coadministration, all showing immunogenicity and safety comparable to sequential administration. That review also found acceptable safety profiles for triple coadministration of COVID-19, respiratory syncytial virus, and influenza vaccines, as well as coadministration with nonrespiratory vaccines.⁵

Taken together, the data give pharmacists a considerably deeper evidence base for a practice already built into routine immunization workflows while underscoring the authors' point that ongoing surveillance—particularly as vaccine formulations continue to change—remains an important part of that picture.

REFERENCES

1. Xie Y, Choi T, Al-Aly Z. Adverse events after same-day COVID-19 and influenza vaccination versus influenza vaccination alone: a target trial emulation. Ann Intern Med. Published online June 30, 2026. doi:10.7326/ANNALS-26-00217

2. Same day administration of COVID-19 and influenza vaccines not associated with increase in adverse events. News release. EurekAlert! June 29, 2026. Accessed July 7, 2026. https://www.eurekalert.org/news-releases/1133268

3. Same-day COVID-19, influenza vaccination does not increase adverse events. Drug Topics. June 30, 2026. Accessed July 7, 2026. https://www.drugtopics.com/view/same-day-covid-19-influenza-vaccination-does-not-increase-adverse-events

4. Getting a flu vaccine and other recommended vaccines at the same time. Centers for Disease Control and Prevention. September 17, 2024. Accessed July 7, 2026. https://www.cdc.gov/flu/vaccines/coadministration.html

5. Scott J, Abers MS, Marwah HK, et al. Updated evidence for Covid-19, RSV, and influenza vaccines for 2025-2026. N Engl J Med. 2025;393(22):2221-2242. doi:10.1056/NEJMsa2514268