Pneumococcal Polysaccharide (PPV23): What It Is and Why You Need It

PPV23, sold under the brand name Pneumovax23, is a vaccine that protects against 23 types of the bacterium Streptococcus pneumoniae, the leading cause of bacterial pneumonia in adults and a major driver of bloodstream infections and meningitis in older people. It was first licensed in 1983 and remains one of the most widely used pneumococcal vaccines in the world, recommended for adults over 65 and for younger people with conditions that put them at higher risk of serious pneumococcal disease. The vaccine’s story, though, is more nuanced than a simple “get the shot” message: how it triggers immunity, how long that protection lasts, and how it fits alongside newer conjugate vaccines are all worth understanding.

What the Vaccine Actually Contains

PPV23 is made from purified pieces of the sugar-like coating (capsular polysaccharide) that surrounds 23 different strains of pneumococcal bacteria. Each dose contains 25 micrograms of polysaccharide from each of those 23 serotypes, dissolved in a small amount of saline with phenol as a preservative. The serotypes covered include 1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F, and 33F.¹ There is no live or killed bacterium in the shot. You cannot get pneumococcal disease from PPV23.

The 23 serotypes were chosen because, at the time of the vaccine’s development, they collectively caused the vast majority of serious pneumococcal infections in adults. That coverage has shifted somewhat over the decades as newer conjugate vaccines used in children have changed which serotypes circulate most, but PPV23 still covers a broad swath of the strains responsible for invasive disease in older adults.²

How PPV23 Triggers Immunity

This is where PPV23 differs from conjugate vaccines in a way that matters practically. Polysaccharide vaccines work through what immunologists call a T-cell-independent response. Your immune system recognizes the sugar coating fragments and produces antibodies against them, but because the process bypasses a key step involving T cells, the immune memory it generates is limited.¹ In plain terms, PPV23 gives you a burst of protective antibodies that fade over time, and your body is not as well-equipped to “remember” and rapidly ramp up production if it encounters the bacterium years later.

Conjugate vaccines like PCV13, PCV15, PCV20, and PCV21 work differently. They chemically attach the polysaccharide fragments to a carrier protein, which pulls T cells into the immune response. That creates stronger, longer-lasting memory. This distinction explains many of the practical quirks of PPV23: why it works less well in very young children, why its protection wanes, and why repeat doses can sometimes backfire.

How Well It Prevents Serious Infection

PPV23’s strongest suit is preventing invasive pneumococcal disease, which includes bloodstream infections and meningitis. A systematic review and meta-analysis of studies in older adults found that effectiveness against invasive disease ranged from roughly 45% in cohort studies to about 73% in clinical trials, with case-control studies landing around 59%.³ Those numbers reflect a genuine and meaningful reduction in a disease that can be fatal, particularly in the elderly.

Real-world data from national programs back this up. A study of adults in Japan between 2013 and 2017 estimated that PPV23 reduced invasive disease caused by vaccine-covered serotypes by about 42%.⁴ Data from the Dutch national vaccination program similarly showed a consistent and substantial drop in vaccine-type invasive disease among older adults, with strong protection in the first three years after vaccination.⁵

Where the evidence gets thinner is pneumonia that does not progress to bloodstream infection. Whether PPV23 meaningfully prevents ordinary community-acquired pneumonia in older adults remains genuinely controversial, with some studies showing a benefit and others finding little effect.⁶ The clearest value of PPV23 is in preventing the most dangerous forms of pneumococcal disease rather than everyday respiratory infections.

How Long Protection Lasts

Because PPV23 generates limited immune memory, antibody levels start declining within months of vaccination. A six-year follow-up study found that antibody concentrations against most serotypes remained somewhat higher than pre-vaccination levels six years out, but had dropped substantially compared to the peak at about four weeks after the shot.⁷ The Dutch data showed the strongest protection in the first three years.⁵

This waning protection is why some guidelines recommend revaccination for people at very high risk. But revaccination introduces its own complication, which is one of the more counterintuitive aspects of polysaccharide vaccines.

The Hyporesponsiveness Problem

Giving a second dose of PPV23 does not simply “boost” the immune response the way you might expect. Instead, prior receipt of PPV23 can actually blunt the body’s ability to respond to a subsequent dose. In a randomized trial involving children, those who had previously received PPV23 showed a “profound lack of response” to all 23 serotypes when given a re-challenge dose, while children who had never received PPV23 mounted a normal response.⁸

This phenomenon, known as hyporesponsiveness, has also been documented in adults with specific conditions. In patients without a functioning spleen who had received multiple doses of PPV23, the repeated polysaccharide exposures blunted their antibody responses to subsequent conjugate vaccines as well.⁹ The mechanism appears to relate to how polysaccharide antigens deplete the pool of B cells capable of responding, without generating the memory cells that would replenish them. This is a practical reason why vaccination schedules now tend to place conjugate vaccines before PPV23 when both are used, rather than the other way around.

Who Should Get PPV23

Pneumococcal vaccination guidelines have grown increasingly complex, but the core principle is straightforward: PPV23 is recommended for people whose risk of serious pneumococcal infection is elevated. Traditionally, that means adults 65 and older and younger adults with certain medical conditions.

The conditions that raise your risk enough to warrant vaccination include:

Chronic lung disease: COPD, asthma, and other conditions where lungs are already compromised
Heart disease and diabetes: conditions that weaken the body’s ability to fight infection
Absent or dysfunctional spleen: the spleen plays a critical role in clearing encapsulated bacteria like pneumococcus from the bloodstream
Immunosuppression: HIV, organ transplant, cancer treatment, long-term steroid or biologic therapy
Sickle cell disease and other hemoglobinopathies: these conditions effectively impair splenic function
Kidney disease and nephrotic syndrome: protein loss and immune dysfunction raise infection risk

Patients with chronic lung diseases who are on steroids or immunosuppressive medications have been specifically recommended to receive both conjugate and polysaccharide pneumococcal vaccines.¹⁰ People without a spleen face a particularly stark risk: pneumococcal bloodstream infections can progress rapidly to overwhelming sepsis. A large study from Spain identified hundreds of invasive pneumococcal disease cases among patients with asplenia over a 25-year period, underscoring how real the threat is for this group.¹¹

Where PPV23 Fits Alongside Conjugate Vaccines

If conjugate vaccines produce better immune memory and stronger responses, why does PPV23 still exist? The answer is serotype breadth. Even the newest conjugate vaccines (PCV20, PCV21) cover 20 or 21 serotypes, while PPV23 covers 23. Several of the serotypes in PPV23 are not included in any currently available conjugate vaccine. For people at high risk, adding PPV23 after a conjugate vaccine can extend protection to those additional serotypes.

Current U.S. guidelines from the Advisory Committee on Immunization Practices give adults several options. You can receive PCV20 or PCV21 alone, or you can get PCV15 followed by PPV23.¹² When PPV23 follows a conjugate vaccine, the conjugate primes the immune system with a T-cell-dependent response first, and PPV23 then broadens serotype coverage. This sequence avoids the hyporesponsiveness problem that occurs when PPV23 is given first.

For people who already received PPV23 in the past and now want the additional protection of a conjugate vaccine, the typical recommendation is to wait at least a year before getting the conjugate shot. The spacing matters precisely because of the blunting effect described earlier.

Why It Does Not Work Well in Young Children

PPV23 was designed to protect adults and older children, and the original research confirmed its usefulness for people over age two against invasive disease caused by the serotypes it covers.¹³ The immune systems of infants and toddlers, however, do not respond robustly to plain polysaccharide antigens. This limitation was recognized early in the vaccine’s development and was the driving motivation behind creating conjugate vaccines in the first place.¹⁴

Interestingly, research has shown that even infants as young as 12 months can mount some immune response to PPV23. In one study, about 71% of infants produced functional immune activity against half of the serotypes tested, and the majority had measurable protective responses for several key strains.¹⁵ But these responses were inconsistent across serotypes, and the hyporesponsiveness problem meant that giving PPV23 to infants could actually compromise their ability to respond to later doses. This is why conjugate vaccines, not PPV23, are the standard for childhood pneumococcal immunization worldwide.

The Serotype Replacement Challenge

Widespread use of conjugate vaccines in children has been one of the great public health successes of the past two decades, dramatically reducing invasive pneumococcal disease caused by the serotypes those vaccines target. But bacteria are not static. As conjugate-vaccine serotypes have been suppressed, other serotypes not covered by those vaccines have filled some of the ecological gap. This phenomenon is called serotype replacement.

For PPV23, serotype replacement has an ironic consequence: the serotypes it covers have become a larger share of the remaining invasive disease in older adults. In England and Wales, PPV23 serotypes comprised an increasing proportion of invasive pneumococcal disease cases among those 65 and older as serotype replacement played out following routine childhood PCV use.² In other words, PPV23 has arguably become more relevant, not less, for the specific strains still causing trouble in older adults.

Global surveillance data confirm that serotype distribution continues to shift, and higher-valency conjugate vaccines are expected to extend the gains against remaining disease.¹⁶ Whether PPV23 will eventually be made obsolete by 20- or 21-valent conjugate vaccines remains an open question, but for now it retains a role because of its unique serotype breadth.

Getting PPV23 Alongside the Flu Shot

A common practical question is whether you can get PPV23 at the same visit as your annual flu vaccine. The answer is yes. A randomized trial in adults 50 and older found that giving an inactivated quadrivalent influenza vaccine at the same time as PPV23 produced immune responses comparable to giving the two shots separately. Both vaccines maintained an acceptable safety profile when co-administered, though injection-site pain was somewhat more common when both were given at once.¹⁷ For people who are already at their doctor’s office or pharmacy for a flu shot, this is a convenient way to avoid an extra visit.

Side Effects

PPV23 is generally well tolerated. The most common reaction is soreness, redness, or swelling at the injection site, which typically resolves within a couple of days. Some people experience mild fever or muscle aches. Serious adverse events are rare. A large-scale analysis of electronic general practice records in England found that patterns of vaccinations and reactions were consistent with the vaccine’s known safety profile, without signals of unexpected problems.¹⁸

People who have had a severe allergic reaction to a previous dose of PPV23 or to any component of the vaccine should not receive it again. Otherwise, the shot is considered safe for the vast majority of adults, including those with chronic diseases and those on immunosuppressive therapy, though the immune response in immunocompromised individuals may be weaker than in healthy adults.

Is It Worth the Cost

From a health-economics standpoint, PPV23 programs have generally been found cost-effective, particularly for older age groups where the burden of pneumococcal disease is heaviest. A cost-effectiveness analysis from China modeled a PPV23 vaccination program for adults aged 60 and over and estimated that it would reduce invasive pneumococcal disease cases by about 10% in the 60-year-old cohort and by roughly 21% in the 70-year-old cohort. The cost per quality-adjusted life year gained was modest, especially for the older group.¹⁹

Adding a conjugate vaccine before PPV23 can improve the calculus further. A Dutch analysis estimated that vaccinating 60-year-olds with PCV13 followed by PPV23 would prevent over 200 additional cases of invasive disease and more than 2,000 additional outpatient pneumonia cases per vaccinated cohort compared with PPV23 alone.²⁰ In most high-income countries, PPV23 is covered by public health programs or insurance for recommended groups, so the out-of-pocket cost to the individual is often zero or minimal.

How the Vaccine Is Made

Manufacturing PPV23 is a complex process that involves growing 23 separate bacterial strains, harvesting the capsular polysaccharide from each, purifying them individually, and then combining all 23 into a single vial. Purification has historically involved organic solvents, though researchers have developed alternative chromatographic methods that eliminate the need for toxic chemicals while maintaining the quality and scalability needed for large-scale production.²¹ Each serotype must meet strict purity and potency standards before being blended into the final product. The entire process, from bacterial culture to finished vaccine, takes months per batch.

The manufacturing challenge also helps explain why polysaccharide vaccines have been slower to evolve than conjugate vaccines. With conjugate vaccines, a manufacturer can add new serotypes relatively systematically by conjugating additional polysaccharides to the same carrier protein. For a pure polysaccharide vaccine, adding a serotype means adding an entirely separate purification stream, and the resulting formulation gets more complex with each addition. Twenty-three serotypes in one shot is already a remarkable feat of pharmaceutical manufacturing, and there are practical limits to how many more could be added before the formulation becomes unwieldy.