What Are the Side Effects of the Pneumonia Shot?

Most people who get a pneumonia shot experience nothing worse than a sore arm for a day or two. Injection-site pain, redness, and swelling are by far the most frequently reported reactions, and they tend to resolve on their own within 48 to 72 hours. Whole-body symptoms like fatigue, mild fever, and muscle aches can also show up, though research suggests these occur at rates not dramatically different from what people experience during any given week without a vaccine. Serious reactions, including severe allergic responses, are genuinely rare.

Local Reactions at the Injection Site

The side effect you are most likely to notice is soreness right where the needle went in. In clinical trials of the newer 20-valent pneumococcal conjugate vaccine (PCV20), injection-site pain was reported by roughly a quarter to two-fifths of participants, making it the single most common complaint.¹ Redness and swelling at the injection site are close behind. A large pharmacovigilance analysis of the U.S. Vaccine Adverse Event Reporting System (VAERS) database confirmed the pattern: injection-site redness, swelling, and pain were the three strongest safety signals among all reported reactions to pneumococcal vaccines.²

These local reactions are driven by the immune system’s immediate response to the vaccine ingredients at the point of entry. Immune cells in the surrounding tissue recognize the injected material, rush to the site, and begin an inflammatory process that makes the area warm, red, and tender. It can feel like a bruise or a mild sunburn. Applying a cool compress and moving your arm gently through the day usually helps.

Whole-Body Symptoms

Beyond the injection site, some people develop fatigue, low-grade fever, headache, or muscle aches. In studies of PCV20 given alongside a flu shot, fatigue was the most commonly reported whole-body symptom, and it showed up a bit more often when both shots were given at the same visit compared to getting them separately. Even then, the fatigue was mild to moderate in most cases and was not considered clinically worrisome.³

An older study specifically tracking systemic symptoms after pneumococcal vaccination found something that surprised the researchers: when they compared how people felt during the week after vaccination to a control week with no vaccination, the rates of fever, rash, muscle pain, fatigue, malaise, and headache were similar or even lower in the postvaccination period.⁴ That does not mean the vaccine never causes these symptoms, but it does suggest that many of the aches and tiredness people attribute to the shot may simply be background noise: the everyday aches that happen to coincide with a recent vaccination. People are primed to notice how they feel in the days after getting a shot, so they credit the vaccine with symptoms they would otherwise shrug off.

What Is Happening Inside Your Body

The side effects of the pneumonia shot are a direct consequence of the immune response the vaccine is designed to trigger. Pneumococcal vaccines deliver pieces of the bacterial capsule, the sugary outer coating that Streptococcus pneumoniae uses to evade your defenses. When these capsule fragments enter your body, they activate several types of immune cells, particularly natural killer cells, certain T cells, and monocytes. The activation is strong enough to cause a burst of inflammatory signaling molecules called cytokines.⁵ Those cytokines are what make you feel achy, fatigued, or feverish. In other words, the side effects are not a sign that something went wrong; they are a sign that your immune system is doing exactly what the vaccine asked it to do.

Different capsule types provoke different degrees of activation. Research on individual capsule components showed that some triggered much stronger immune-cell responses than others.⁵ This helps explain why newer vaccines that cover more bacterial types might, in theory, produce a slightly more noticeable reaction, and it is why researchers keep a close eye on side-effect profiles whenever the valency of a vaccine goes up.

How Newer, Higher-Valent Vaccines Compare

Several pneumococcal vaccines are now in use or recently approved, covering different numbers of bacterial strains. The older 13-valent conjugate vaccine (PCV13) has been the workhorse for years, but 15-valent (PCV15) and 20-valent (PCV20) options have entered the picture. A natural question is whether adding more bacterial targets to the shot makes side effects worse.

For infants, the answer so far is reassuring. A systematic review and meta-analysis comparing PCV15 and PCV13 found that the risk of adverse events in babies was comparable between the two vaccines. Among adults, PCV15 recipients had a slightly higher overall risk of side effects, but the rate of serious adverse events was no different between groups.⁶

A similar story emerged for PCV20. In a multinational randomized trial of a four-dose infant series, the frequencies of local reactions and whole-body symptoms were generally similar between children who received PCV20 and those who received PCV13. Injection-site pain and irritability remained the top complaints in both groups, with most events rated mild or moderate. No serious adverse events were linked to the study vaccines.¹ The vaccine also performed safely in late preterm infants and when given alongside other routine childhood immunizations.

In short, broader coverage has not come at a steep cost in terms of side effects. The jump from 13 to 15 or 20 strains produced side-effect profiles that look very much like the one clinicians were already used to.

Getting the Pneumonia Shot and Flu Shot Together

Many adults, especially older ones, are offered the pneumococcal and influenza vaccines at the same visit. This raises a practical question: does getting both at once make side effects worse?

For adults receiving PCV20 and a flu shot simultaneously, the data suggest a modest uptick in fatigue compared to receiving the vaccines separately, but most of it was mild or moderate and resolved quickly.³ In a study of elderly individuals, including those at higher risk due to chronic conditions, researchers found no side effects at all when the two vaccines were given at the same time, and concluded the practice was safe.⁷

So while co-administration can add a bit of extra fatigue, there is no evidence it creates dangerous reactions. If your doctor offers both shots at the same visit and you would rather not make two trips, the evidence supports that decision.

Febrile Seizures in Young Children

Parents of young children sometimes worry about febrile seizures, brief convulsions triggered by a spike in body temperature. These are one of the more alarming-sounding vaccine side effects even though they are almost always harmless and leave no lasting effects.

Research looking at PCV13 given alone found a small but real increase in febrile seizure risk in the days after vaccination, with the rate about one and a half times higher than during unexposed periods. When PCV13 and the inactivated influenza vaccine were given at the same visit, the risk was roughly three times higher than baseline, suggesting an interaction between the two vaccines.⁸ The influenza vaccine alone did not appear to raise the risk independently.

This is worth knowing but needs context. Febrile seizures already happen in about 2 to 5 percent of children between six months and five years, usually during ordinary illnesses that cause fever. A short-lived fever after vaccination can, in susceptible children, push past the same threshold. The seizures look frightening, but they virtually never cause brain damage or epilepsy. Pediatricians are aware of the interaction and can discuss whether to separate the pneumococcal and flu shots if your child has a history of febrile seizures.

Severe Allergic Reactions

True anaphylaxis to a pneumococcal vaccine is extremely rare, but it has been documented. In one of the few explored cases, a child experienced anaphylaxis after a first injection of the 23-valent polysaccharide vaccine. Skin testing and specific antibody testing confirmed that the reaction was a genuine allergic response to pneumococcal antigens in the vaccine.⁹

A second case highlighted a different pathway. A child had previously tolerated three doses of the 7-valent conjugate vaccine without trouble, but then experienced anaphylaxis upon receiving the 23-valent polysaccharide vaccine as a fourth dose. Investigators concluded that the earlier conjugate vaccine doses may have sensitized the child’s immune system, priming it to overreact to the polysaccharide version.¹⁰ That finding was unusual and represents an edge case. For the vast majority of people, switching between vaccine types poses no allergic risk.

The standard precaution applies: after any vaccination, you should wait at the clinic for about 15 minutes. This is exactly the window in which anaphylaxis would typically appear, and medical staff are equipped to treat it immediately.

When Local Reactions Get Dramatic

Occasionally, the expected injection-site reaction escalates into something that looks alarming. A small case series documented five adults who developed cellulitis-like reactions after receiving the 23-valent polysaccharide vaccine. Their arms became significantly red and swollen, they developed fevers, and blood work showed elevated white blood cell counts. Four of the five were admitted to the hospital, and some were treated with intravenous antibiotics before it became clear the reaction was inflammatory rather than infectious.¹¹

This kind of reaction can easily be mistaken for a skin infection, and it often is. Four of the five patients had received both the flu shot and the pneumococcal vaccine in the same arm, but the inflammatory reaction appeared in the arm that got the pneumococcal vaccine. If you develop spreading redness, warmth, and swelling around the injection site a day or two after your shot, it is worth having it evaluated, but know that in many cases the explanation is a strong inflammatory response rather than a bacterial infection.

People with HIV and Other Immune Conditions

People with compromised immune systems, including those living with HIV, are among those most strongly recommended to receive pneumococcal vaccination because they face higher risks from pneumococcal disease. A reasonable concern is whether the vaccine could worsen their underlying condition.

In a study of the 23-valent polysaccharide vaccine in HIV-positive individuals who were former injection drug users, the vaccine was well tolerated. It caused no meaningful changes in CD4+ cell counts, and it did not increase either plasma viral load or proviral DNA levels.¹² In practical terms, getting the shot did not set their disease management back. The researchers did note that the antibody response to a single dose was poor, which is a separate problem of reduced effectiveness rather than safety, and one reason why conjugate vaccines are now generally preferred in this population.

For people on immunosuppressive medications for autoimmune diseases or organ transplants, the safety picture is broadly similar: the vaccines are well tolerated, though the immune response may be blunted. The relevant risk in these groups is not that the vaccine will cause worse side effects, but that it may not work as well.

Who Reports Side Effects Most Often

Patterns in large safety databases give some insight into who is more likely to notice or report side effects. The VAERS analysis of over 157,000 individuals who received pneumococcal vaccines found that women accounted for a larger share of adverse-event reports than men, with females making up about 54 percent of reports compared to roughly 37 percent for males.² Whether this reflects a genuine biological difference in reactogenicity, a difference in reporting behavior, or both, is hard to untangle. Studies across many vaccine types have found similar sex-based reporting gaps.

The same database showed that the largest share of reports, about 38 percent, came from individuals under 18, which reflects the fact that infants and young children receive multiple doses on a fixed schedule and their parents or pediatricians tend to be diligent reporters. Most adverse events appeared within the first day after vaccination, with a median onset of day zero. Among all outcomes, about 44 percent of cases resulted in complete recovery, while roughly 15 percent involved hospitalization.² That hospitalization figure sounds high until you remember that VAERS captures a skewed sample. People with minor sore arms rarely bother filing a report; people who end up in the emergency room almost always do. The database over-represents serious cases by design, and it cannot prove that a vaccine caused the reported event, only that the event happened after vaccination.

Comparing Conjugate and Polysaccharide Vaccines

Two broad categories of pneumococcal vaccine exist, and their side-effect profiles differ in some subtle ways. Conjugate vaccines (PCV13, PCV15, PCV20) attach the bacterial sugar to a carrier protein, which teaches the immune system more effectively and produces a stronger memory response. Polysaccharide vaccines (PPSV23) deliver the raw sugar without a protein carrier. Both types are used in adults, though recommendations vary by age and risk profile.

In the VAERS database, the polysaccharide vaccine (PPSV23) accounted for about 49 percent of all reported adverse events, while PCV13 accounted for about 28 percent.² Part of this difference simply reflects how many doses of each vaccine have been administered over the years and in which populations. PPSV23 has been around since the 1980s and was for a long time the primary adult vaccine, so it has an enormous denominator. Still, the polysaccharide vaccine has historically been associated with more prominent injection-site reactions, especially on revaccination. The case series of large inflammatory reactions mentioned earlier all involved the polysaccharide vaccine.¹¹

The shift in clinical practice toward conjugate vaccines, and particularly the newer higher-valent conjugate vaccines, means many adults will now receive a conjugate vaccine as their primary pneumococcal immunization. Based on available trial data, the side-effect experience with these conjugate vaccines is generally mild and comparable across valency levels, which is good news as coverage expands.

The Transition from PCV7 to PCV13 in Children

When Australia introduced PCV13 to replace the older 7-valent conjugate vaccine (PCV7), health authorities tracked adverse events closely. In the first year after the switch, surveillance picked up seven categories of events reported at higher rates with PCV13 compared to PCV7. That sounded concerning at first, but a follow-up analysis covering the next 12 months told a different story: all seven of those initially elevated categories had dropped back to rates that were no longer statistically different from the PCV7 era. Serious adverse events were no more common with PCV13 than they had been with PCV7 at any point.¹³

This pattern is common when a new vaccine replaces an old one. Clinicians and parents are on high alert for anything different, reporting rates spike simply because vigilance is higher, and the numbers settle once the vaccine becomes familiar. It is a good illustration of why snapshot data from the first months after a vaccine launch can look scarier than the long-term picture warrants.