Is the COVID Vaccine in the Flu Shot?

No approved vaccine currently on the market contains both COVID-19 and influenza components in a single shot. The two vaccines remain separate injections, though they can be given at the same appointment. That said, several pharmaceutical companies are deep into clinical trials for combination vaccines that would put both into one needle, and the results so far look genuinely promising. Understanding what exists today, what is coming, and what the science says about giving both vaccines together can clear up a lot of the confusion around this question.

What You Actually Get at the Pharmacy Today

When you walk into a pharmacy or clinic for your fall vaccinations, you receive two distinct shots: one for influenza and one for COVID-19. They are manufactured separately, stored separately, and injected separately, usually one in each arm. Your pharmacist is not secretly combining them, and no approved product blends the two. The flu shot targets influenza virus strains selected each year by a global surveillance network, while the COVID-19 vaccine targets the SARS-CoV-2 spike protein updated to match circulating variants. These are fundamentally different viruses, and the vaccines use different formulations to address them.

The reason this question comes up so often is practical. Many people get both shots in the same visit during the fall season, and when two injections happen within minutes of each other, it is natural to wonder whether they are somehow the same product or whether mixing them causes problems. They are not the same product, and the mixing question has actually been studied quite thoroughly.

Is It Safe to Get Both Shots at the Same Visit?

Getting a COVID-19 vaccine and a flu shot at the same appointment is not just common practice; it is backed by solid safety data. A review of adverse event reports submitted to the national vaccine safety surveillance system between July 2021 and June 2022 found no unusual or unexpected patterns when mRNA COVID-19 vaccines and seasonal influenza vaccines were co-administered. The most frequently reported side effects among non-serious reports were injection-site reactions, headache, and general pain, which are the same side effects each vaccine causes on its own.¹

In older adults specifically, a clinical trial looked at giving a high-dose quadrivalent flu vaccine alongside a booster dose of Moderna’s COVID-19 vaccine in people 65 and older. No safety concerns or immune interference were observed, meaning neither vaccine weakened the other’s ability to generate a protective immune response.² This is reassuring because older adults are more vulnerable to both infections and are more likely to receive enhanced flu vaccine formulations.

Real-world data reinforces the trial findings. A large comparative effectiveness study found that getting the updated Pfizer COVID-19 vaccine alongside a seasonal influenza vaccine produced similar protection against both COVID-19 and influenza-related outcomes as giving the two vaccines at separate visits.³ There may even be a slight bonus: one laboratory study found that people who received both vaccines concurrently had higher antibody responses against SARS-CoV-2 at peak immunity and six months later, compared to those who received the COVID-19 vaccine alone.⁴ The mechanism behind this potential boost is not fully understood, but the finding is intriguing.

Combination Vaccines in Development

While today’s COVID and flu vaccines are separate, the vaccine industry is actively working to change that. Several companies have combination candidates in late-stage clinical trials that would deliver protection against both viruses in a single injection. The appeal is obvious: one shot, one appointment, less hassle. But proving that a combination vaccine works as well as two separate vaccines is a high scientific bar, and the results so far vary by company and technology.

Moderna’s mRNA-1083

Moderna’s candidate, called mRNA-1083, is the furthest along and arguably the most promising. It uses the same mRNA technology as Moderna’s COVID-19 vaccine but encodes both SARS-CoV-2 spike protein and four influenza hemagglutinin proteins in a single formulation. In a large randomized trial involving roughly 8,000 adults across two age groups, a single dose of mRNA-1083 triggered immune responses that were at least as strong as getting licensed flu and COVID vaccines separately. In fact, mRNA-1083 generated statistically higher immune responses against three influenza strains (H1N1, H3N2, and B/Victoria) and against the SARS-CoV-2 Omicron variant compared to the individual vaccines.⁵ Among adults aged 50 to 64, the combo outperformed the standard-dose flu vaccine on all four influenza strains. Among those 65 and older, it outperformed the high-dose flu vaccine on three of four strains.⁶

Pfizer’s Combination Candidate

Pfizer and BioNTech are developing their own mRNA-based combination vaccine. Early-phase trials in healthy adults aged 18 to 64 showed robust immune responses against influenza A, influenza B, and SARS-CoV-2 strains. However, the picture is more complicated than Moderna’s. In ongoing phase 3 trials enrolling over 8,000 adults, a trivalent influenza formulation generated strong influenza A responses but fell short on the influenza B strain, failing to meet the statistical benchmark for non-inferiority.⁶ That does not mean the program is dead, but it does mean Pfizer’s combination candidate needs further refinement before it can match the performance of existing individual vaccines across all targeted strains.

Novavax’s Protein-Based Approach

Not all combination vaccines under development rely on mRNA. Novavax is pursuing a different approach using recombinant protein nanoparticles paired with its Matrix-M adjuvant, the same technology platform behind its standalone COVID-19 vaccine. The company’s COVID-Influenza Combination vaccine, or CIC, bundles recombinant SARS-CoV-2 spike protein with quadrivalent influenza hemagglutinin antigens.⁷

Phase 1/2 trial data showed that CIC formulations generated antibody responses against both influenza and SARS-CoV-2 strains that were comparable to the standalone reference vaccines, with a similar safety profile.⁷ Researchers did observe some evidence of antigen interference, meaning the two components slightly dampened each other’s responses, but the overall antibody levels remained comparable to licensed enhanced influenza comparators and the authorized prototype COVID-19 vaccine.⁸ This antigen interference is one of the core scientific puzzles that all combination vaccine developers have to solve. Novavax is now testing optimized antigen concentrations in adults 65 and older.⁹

The Antigen Interference Problem

Combining two vaccines into one shot sounds straightforward, but the immune system does not always cooperate. When multiple antigens are delivered simultaneously in the same formulation, they can compete for the body’s attention. Immune cells may mount a strong response to one component while responding less vigorously to another. This phenomenon, called antigen interference, is the central technical challenge facing all combination vaccine efforts.

The Novavax CIC data illustrate this clearly: researchers saw some blunting of individual responses when both antigens were present, even though the overall results remained in an acceptable range.⁸ Moderna’s mRNA-1083, by contrast, appeared to sidestep this issue, actually exceeding individual vaccines on most measures.⁵ Whether this reflects something inherent about mRNA technology or differences in dose optimization is an open question. What is clear is that antigen interference is not a dealbreaker, but it does mean that simply mixing two existing vaccines together in one vial would not work. Each combination product requires its own careful dose-finding and reformulation process.

This is also why co-administering two separate shots at the same visit is not the same thing as a combination vaccine. When you get a flu shot in one arm and a COVID shot in the other, each formulation is optimized independently. The immune system encounters them at different sites and processes them through different local lymph nodes. A true combination vaccine delivers everything to the same injection site, which is a harder immunological problem to solve.

Why One Shot Matters More Than Convenience

The push toward combination vaccines is not just about saving people a few minutes at the pharmacy. Vaccination rates for both COVID-19 and influenza remain stubbornly low in many populations, and every additional barrier, whether it is scheduling, cost, needle anxiety, or simply having to remember two separate appointments, reduces uptake. As the number of recommended adult vaccines continues to grow, combination vaccines represent one of the most practical strategies for keeping people protected.¹⁰

Pediatric medicine figured this out decades ago. Childhood combination vaccines, like those bundling protection against diphtheria, tetanus, pertussis, polio, and hepatitis B, have been a cornerstone of immunization programs for over 70 years. They work, they are safe, and they dramatically simplify the vaccination schedule for both parents and pediatricians. Adult combination vaccines are trying to replicate that success, but the path has been slower because the science of combining adult vaccine formulations presents different challenges.

There are also behavioral factors at play. Research on vaccine intentions has found that younger adults, lower-income individuals, and those without close personal experience of serious illness tend to have lower vaccine acceptance.¹¹ A single combination shot could reduce the decision points from two to one, potentially reaching people who might otherwise skip the COVID vaccine or the flu vaccine but would accept a single injection covering both.

What Is Not Being Combined

Some of the anxiety around this topic seems driven by a worry that COVID-19 vaccines might be silently added to flu shots without people’s knowledge. This is not happening and could not happen without new regulatory approvals, updated product labeling, and changes to informed consent procedures. Every vaccine administered in the United States has its own product name, lot number, and ingredient list that must be communicated to the patient and documented in their medical record. Pharmacists and nurses are required to tell you what they are injecting. If a combination flu-COVID product is eventually approved, it will be labeled as a combination vaccine and you will know you are receiving one.

It is also worth noting that a combination vaccine would not be the same thing as a COVID vaccine hidden inside a flu shot. It would be an entirely new product developed, tested, and approved specifically as a combination. The formulation, dosing, and manufacturing process would be different from either standalone vaccine. Think of it less like someone slipping an extra ingredient into your soup and more like a chef designing an entirely new dish that happens to incorporate flavors from two existing ones.

The Spillover Effect on Vaccine Attitudes

The pandemic reshaped how many people think about vaccines in general, not just COVID-19 vaccines. Research has documented a spillover effect in which strong feelings about COVID-19 vaccination, whether positive or negative, have bled into attitudes toward routine vaccines like the flu shot.¹² For some people, distrust of the rapid COVID-19 vaccine development process created broader skepticism about immunization. For others, the experience of getting a COVID vaccine with minimal side effects reinforced confidence in vaccination as a whole.

This dynamic matters for the rollout of any future combination vaccine. A product that merges flu and COVID protection into one injection will inevitably inherit the political and emotional baggage attached to COVID-19 vaccination. Manufacturers and public health agencies will need to communicate clearly about what these products contain, how they were tested, and how they differ from the individual vaccines people already know. Transparency about clinical trial results, including where a combination candidate fell short on certain strains, will be essential for building trust.

Beyond Flu and COVID

The ambitions of combination vaccine developers extend beyond just influenza and COVID-19. Moderna has publicly discussed plans for mRNA vaccines that could protect against influenza, COVID-19, and respiratory syncytial virus (RSV) in a single shot. RSV is a major cause of hospitalization in older adults and young children, and standalone RSV vaccines have only recently become available. A three-in-one respiratory vaccine would address the trio of viruses that drive the most severe respiratory illness each winter season.

Whether three-pathogen combination vaccines can overcome antigen interference challenges remains to be seen. The more components you add, the more opportunities there are for immune responses to step on each other. But the potential public health payoff is enormous. Imagine a single fall vaccination visit that covers all three major respiratory threats, the way a single childhood visit covers five or six diseases at once. That is the horizon the field is working toward, and the flu-COVID combination vaccines currently in trials are the first meaningful steps in that direction.

Preclinical work has already shown proof of concept. In animal models, a combination recombinant protein vaccine targeting both influenza and SARS-CoV-2 protected mice from both infections, with immune responses equivalent to those generated by standalone vaccines for each virus.¹³ Animal data does not always translate perfectly to humans, but it reinforces that the concept is biologically sound. The remaining questions are about optimizing formulations and navigating the regulatory process, not whether combination respiratory vaccines can work in principle.

When Could a Combination Shot Be Available?

Moderna’s mRNA-1083 is the closest to the finish line, with phase 3 data already published and regulatory submissions potentially on the near-term horizon. Pfizer’s candidate needs to resolve its influenza B shortfall before it can advance to approval. Novavax’s protein-based approach offers an alternative for people who prefer non-mRNA vaccines but is still in earlier clinical development stages for its combination product.

Even with strong trial data, the regulatory pathway for adult combination vaccines is not as well-trodden as it is for childhood combination shots. Regulators will need to assess not just whether the combination vaccine matches the individual vaccines on immune response, but also whether it provides adequate real-world protection over a full respiratory season. The strain composition for both the influenza and COVID-19 components will need to be updated annually, adding a layer of manufacturing complexity that standalone vaccines do not face in the same way. These are solvable problems, but they mean that even optimistic timelines for approval involve navigating a process with few direct precedents in adult immunization.