What Are the Key Sanofi Pasteur Vaccines?

Sanofi Pasteur, the vaccines division of the French pharmaceutical company Sanofi, produces one of the broadest portfolios in the industry, spanning flu shots for older adults, pediatric combination vaccines, travel immunizations, and products aimed at some of the world’s most dangerous tropical infections. Some of its vaccines have been household names for decades, while others reflect newer platform technologies still working their way through regulatory approvals around the globe. The portfolio is worth understanding not just as a product catalog but because the science behind each vaccine tells a story about how modern immunization is evolving.

High-Dose and Recombinant Influenza Vaccines

Sanofi Pasteur’s influenza lineup is arguably its most commercially visible product family. The company manufactures Fluzone High-Dose (now updated to a quadrivalent formulation), which is specifically designed for adults aged 65 and older. The rationale is straightforward: aging immune systems respond less vigorously to standard flu shots. A large randomized trial of nearly 32,000 older adults found that the high-dose version provided about 24% better protection against laboratory-confirmed influenza compared with the standard-dose vaccine, along with significantly higher antibody levels after vaccination.¹ Subsequent meta-analyses and observational studies have consistently supported that relative advantage across different flu seasons and age subgroups within the over-65 population.²

Sanofi also acquired and now manufactures Flublok, the first recombinant hemagglutinin influenza vaccine licensed by the FDA. Rather than growing flu virus in chicken eggs, Flublok uses insect cell cultures and baculovirus expression technology to produce hemagglutinin proteins that are close analogues of the proteins found on circulating influenza strains.³ This matters for a practical reason that often gets overlooked: when flu viruses are adapted to grow in eggs, they can pick up mutations that change the hemagglutinin protein slightly, which sometimes reduces how well the vaccine matches the circulating strain. The recombinant manufacturing process sidesteps that vulnerability entirely.⁴ For people with severe egg allergies, Flublok also removes any egg-related safety concern, though that population is relatively small.

Vaxelis and Pediatric Combination Vaccines

One of Sanofi Pasteur’s more impactful recent products is Vaxelis, a fully liquid hexavalent vaccine developed jointly with Merck. A single injection covers diphtheria, tetanus, pertussis (with five acellular pertussis antigens), polio, Haemophilus influenzae type b (Hib), and hepatitis B. Pivotal trials showed that Vaxelis met predefined immunogenicity criteria and was noninferior to the separate licensed vaccines it replaces, with a tolerability profile that looked similar to the comparator vaccines.⁵ Trials in infants specifically confirmed high seroprotection rates across all six antigen components, with no vaccine-related serious adverse events reported.⁶

The value of combination vaccines goes beyond convenience. Research consistently shows that children who receive combination vaccines are more likely to complete their full immunization series on time. One U.S. study found that children receiving at least one combination vaccine were roughly 2.5 times more likely to complete the recommended series by 24 months compared with children receiving only single-antigen shots.⁷ Similar findings have emerged internationally; a Chinese study found a roughly fourfold increase in the likelihood of completing the three-dose Hib schedule among children who received combination rather than single-antigen doses.⁸ Fewer injections mean fewer clinic visits, fewer tears, and fewer opportunities for a family to fall behind schedule.

Vaxelis has also been studied in premature infants, a population that often gets less attention in vaccine trials but is especially vulnerable to infectious disease. A safety and immunogenicity analysis found that premature infants mounted protective immune responses at rates comparable to the overall study population, with adverse event profiles that were similar as well.⁹ Follow-up studies examining booster doses have confirmed that immune responses remain strong when a Vaxelis booster is given after a primary series, whether the primary series used Vaxelis or a different hexavalent product.¹⁰

Meningococcal Conjugate Vaccine

Sanofi Pasteur manufactures MenQuadfi (known by the shorthand MenACYW-TT), a quadrivalent meningococcal conjugate vaccine that uses tetanus toxoid as its carrier protein. It protects against meningococcal disease caused by serogroups A, C, W, and Y, which together account for a significant share of invasive meningococcal cases worldwide. One concern with meningococcal vaccines has always been how long protection lasts, particularly in children vaccinated early in life. A recent five-year follow-up study found that antibody levels and seroprotection rates remained higher than pre-vaccination levels five years after the priming dose, and a booster given at that point generated strong responses, with seroresponse rates above 93% for all four serogroups.¹¹ That durability data is reassuring, especially given that meningococcal disease, while rare, can be devastating when it strikes.

Yellow Fever Vaccine and Fractional Dosing

Sanofi Pasteur has long been a major producer of the yellow fever 17D vaccine, one of the most successful vaccines ever developed. A single standard dose provides lifelong protection for the vast majority of recipients. But global supply has been an intermittent problem, particularly when outbreaks flare in sub-Saharan Africa or South America. This led to an important practical question: could a fraction of the standard dose still work?

The answer, based on clinical trial data, appears to be yes. Fractional-dose yellow fever vaccination, using one-fifth of the standard dose given intradermally, is now accepted as an emergency measure during outbreaks. A randomized controlled trial followed participants for more than a decade and found that 98% of those receiving the fractional dose still had protective levels of neutralizing antibodies after ten years, nearly identical to the 97% rate in the standard-dose group.¹² Broader application of fractional dosing outside of emergency settings is still under discussion, but the existing evidence suggests that people who mount an initial protective response after a fractional dose maintain that protection for at least ten years and possibly longer.¹³ This kind of dose-sparing strategy could dramatically stretch limited global supply during the next major outbreak.

The Dengvaxia Story

No discussion of Sanofi Pasteur’s vaccine portfolio is complete without addressing Dengvaxia, the world’s first licensed dengue vaccine, and the controversy that followed its rollout. Dengvaxia is a live-attenuated tetravalent vaccine built on a yellow fever vaccine backbone. It showed meaningful protection in clinical trials among people who had previously been infected with dengue. The problem emerged in the long-term safety data: children who had never been exposed to dengue before vaccination (seronegative individuals) experienced higher rates of hospitalization and more severe disease upon subsequent natural dengue infection.¹⁴ The suspected mechanism is antibody-dependent enhancement, where the antibodies generated by the vaccine actually help the virus enter cells more efficiently during a later natural infection, making disease worse rather than preventing it.¹⁵

The fallout was significant. In 2018, the World Health Organization revised its recommendation, stating Dengvaxia should only be given to individuals with confirmed prior dengue infection. That restriction severely limits the vaccine’s practical usefulness in endemic countries where blood testing for prior infection is expensive and logistically difficult. Dengvaxia remains licensed in some countries and continues to provide real benefit for seropositive individuals, reducing hospitalization and severe outcomes in that group. However, Sanofi has announced it will discontinue manufacturing and distribution of Dengvaxia, with availability expected to end after August 2026.¹⁶ The episode has become a cautionary case study in vaccinology, underscoring how a vaccine can work well for one population while actually causing harm in another.

Rabies Vaccines and Evolving Schedules

Verorab, Sanofi Pasteur’s purified Vero cell rabies vaccine, has been a WHO-approved product for both pre-exposure and post-exposure prophylaxis for decades. Over twenty years of clinical use documented across thousands of patients has established its reliability for both intramuscular and intradermal regimens.¹⁷ The traditional pre-exposure schedule involves multiple doses spread over several weeks, which creates a practical problem for travelers who decide to visit a rabies-endemic area on short notice.

Recent research has explored whether abbreviated schedules might work. A phase III trial tested a one-week pre-exposure regimen with Verorab, given either intramuscularly or intradermally, and found that seroconversion rates were high within 14 days and that robust anamnestic (memory) responses appeared rapidly when a simulated post-exposure booster was given a year later.¹⁸ An even more aggressive study looked at a single-dose approach: one intramuscular dose of Verorab, followed by simulated post-exposure treatment at least 60 days later. All participants achieved protective antibody levels seven days after commencing the simulated post-exposure doses, though younger adults responded more strongly than those over 50.¹⁹ The takeaway for travelers is that even a single pre-exposure dose, if a full series is not possible before departure, is better than skipping vaccination entirely.

Typhoid Vaccination for Travelers

Typhim Vi, Sanofi Pasteur’s typhoid Vi polysaccharide vaccine, is a single-injection option commonly used by travelers heading to areas where typhoid fever is endemic. Unlike live oral typhoid vaccines, it requires no multi-day dosing schedule and has no restrictions around concurrent antibiotic use. However, the protection it provides is not permanent. A study tracking antibody levels in adults living in non-endemic areas found that anti-Vi antibody concentrations declined progressively over three years, supporting the standing U.S. recommendation to revaccinate every two years for people with ongoing exposure risk.²⁰ If you traveled to South Asia five years ago and got a typhoid shot but are planning another trip, you will need a booster.

Polio Vaccines and Cold-Chain Improvements

Sanofi Pasteur produces IPOL, an inactivated poliovirus vaccine (IPV) that has been a cornerstone of polio vaccination in countries that have moved away from the oral vaccine. With polio eradication tantalizingly close yet persistently incomplete, research continues into next-generation inactivated vaccines that might be easier to stockpile and distribute in low-resource settings. One promising development involves IPV produced from Sabin strains (the attenuated strains originally developed for oral vaccines) inactivated using ultraviolet light rather than formalin. Early results show this approach preserves antigenic quality even after freeze-thaw cycles, which is a meaningful advantage for maintaining emergency stockpiles and navigating imperfect cold chains in tropical settings.²¹ Whether Sanofi Pasteur ultimately manufactures such a product at scale remains to be seen, but the research reflects the broader direction of polio vaccine development.

RSV Prevention in Infants

Respiratory syncytial virus (RSV) is the leading cause of infant hospitalization in the United States, and Sanofi has partnered with AstraZeneca to bring nirsevimab (brand name Beyfortus) to market. Nirsevimab is not a traditional vaccine but a long-acting monoclonal antibody given as a single injection to protect infants through their first RSV season. A meta-analysis covering 27 observational studies across five countries found real-world effectiveness of about 83% against RSV hospitalization, 81% against intensive care admission, and 75% against lower respiratory tract infection.²² Beyfortus received FDA approval in 2023 alongside Pfizer’s maternal RSV vaccine, Abrysvo, giving families and clinicians two distinct approaches to infant RSV prevention for the first time.²³

The distinction matters: Abrysvo is given to the pregnant mother so she passes protective antibodies to her baby before birth, while Beyfortus is given directly to the infant. For babies born outside RSV season whose mothers were not vaccinated during pregnancy, Beyfortus can be administered at the start of the RSV season. Supply constraints in the first season after approval limited availability, but the real-world data has been encouraging enough that RSV immunoprophylaxis is rapidly becoming a standard part of infant care.

COVID-19 Vaccine Platform

Sanofi Pasteur’s COVID-19 vaccine program took a different path from the mRNA vaccines that dominated early pandemic rollouts. The company developed a protein-based vaccine using a stabilized prefusion spike protein (called CoV2 preS dTM) combined with GSK’s AS03 adjuvant. While this approach arrived later than the mRNA and adenoviral-vector vaccines, the protein subunit platform showed particular promise as a booster. A bivalent formulation containing both the ancestral and Beta variant spike proteins induced higher cross-neutralizing antibody titers against Omicron subvariants compared with boosting using ancestral-only formulations.²⁴

Head-to-head comparisons were encouraging. A trial comparing the Beta-variant monovalent booster against a BNT162b2 (Pfizer) mRNA booster found that the Sanofi protein-based shot induced roughly 2.5-fold higher neutralizing antibody titers against both Omicron BA.1 and BA.4/5 at one month, with better persistence of those antibodies at three months.²⁵ Sanofi ultimately chose not to pursue its COVID-19 vaccine commercially, but the adjuvanted recombinant protein platform it built for the pandemic remains in the company’s technology toolkit and could be adapted for future respiratory virus threats.

Adjuvant Technology Behind the Scenes

An underappreciated aspect of Sanofi Pasteur’s portfolio is its investment in adjuvant technology. Adjuvants are the ingredients added to vaccines to amplify the immune response, and the choice of adjuvant can determine whether a vaccine works with a smaller amount of antigen, a critical advantage during pandemics when antigen supply is limited. Sanofi developed AF03, an oil-in-water emulsion adjuvant that was licensed for use during the 2009 H1N1 pandemic in a vaccine called Humenza, though the product was never commercially distributed. Like other emulsion adjuvants, AF03 demonstrated antigen-sparing properties and induced stronger immune responses compared with non-adjuvanted vaccine.²⁶ AF03 has since been tested in early-stage clinical trials for SARS-CoV-2 vaccines, keeping it in the active pipeline. For the COVID-19 booster program described above, Sanofi partnered with GSK to use the AS03 adjuvant instead, showing the company’s willingness to mix and match adjuvant platforms depending on the application.

Adjuvant flexibility is genuinely important for pandemic preparedness. If a new pathogen emerges and vaccine manufacturers need to stretch limited antigen supplies to cover billions of people, having a proven adjuvant that allows each dose to use less protein can be the difference between vaccinating a few hundred million people and vaccinating several billion. Sanofi’s dual investment in its own AF03 and its working relationship with GSK’s AS03 gives it options that not every manufacturer has.