Pneumonia: Independent Evidence on Treatment and Vaccines

Table of contents

• Evidence summary
• What pneumonia is, and how it is classed
• How it develops and how it is scored
• What works and what does not
• Evidence by question
• Risks and complications
• Who is at higher risk
• Trial doses, durations and vaccine schedules
• Follow the money: who makes it and who funded the evidence
• Related research
• Frequently asked questions
• Sources and funding notes

Evidence summary

Independent evidence and credibility scorecard

Independence tiers: 1 = regulator, government, public hospital or public-funded research with no declared commercial funding; 2 = academic or Cochrane team with no declared commercial funding for the work, or a funding statement we could not open; 3 = independent authors analysing mostly manufacturer-run trials, or minor declared industry ties; 4 = manufacturer-funded or manufacturer-authored. Credibility runs from A (highest) to D.

Note on clustering: the vaccine efficacy evidence comes mainly from manufacturer-run trials (Pfizer and GSK), while the most independent evidence on severity scoring is public and older. Most of our sources are from Europe and the US. The corticosteroid evidence comes from a French public-sponsored trial and a meta-analysis by authors in the US, Taiwan and Singapore. The supplement evidence is almost entirely from Europe and Australia.

What pneumonia is, and how it is classed

Pneumonia is an infection of the lung tissue. It is usually caught in the community (community-acquired pneumonia, CAP) or acquired in hospital. CAP is the form most adults meet. NICE's 2025 guideline covers diagnosing and managing pneumonia in babies, children and adults, and includes separate assessment tools for hospital-acquired pneumonia (NICE NG250).

Two groups of causes matter for treatment. Typical bacteria, especially Streptococcus pneumoniae, cause most bacterial CAP. Aspiration pneumonia happens when food, fluid or stomach contents enter the lungs, mostly in debilitated people with swallowing problems. A 2011 review describes aspiration pneumonia as often presenting as community-acquired pneumonia, with dysphagia as the key underlying factor (Marik, Current Opinion in Pulmonary Medicine 2011).

How it develops and how it is scored

Most of the decisions in adult pneumonia depend on two things: how sick the person is, and what is causing the infection. The first is estimated with a score. CURB-65 uses five items, one point each: confusion, urea above 7 mmol/l, respiratory rate of 30 or more, low blood pressure (systolic below 90 or diastolic 60 or less), and age 65 or older (Lim et al. 2003). The score was derived from 80% of combined data from three prospective studies, which together included 1,068 patients. A higher score means higher 30-day risk of death, and the score is meant to be used alongside clinical judgement, not in place of it.

The second question, what is causing the infection, is harder. NICE NG250 recommends pneumococcal urinary antigen tests to support de-escalation to a narrower antibiotic, and Legionella urinary antigen tests if the person has risk factors for Legionella infection (NICE NG250, section 1.4).

What works and what does not

Evidence by question

How long should antibiotics be given?

This is the question people ask most, and the honest answer is that the best independent trials are small. In the Dutch trial, adults with mild to moderate-severe pneumonia who had substantially improved after three days of intravenous amoxicillin were randomised to five more days of oral amoxicillin or placebo. The trial enrolled 119 people, 63 on oral amoxicillin and 56 on placebo. The primary outcome was clinical success at day 10, which was 93% in both groups. Day-28 clinical success was 90% in the three-day group and 88% in the eight-day group, with a difference of 2.0% (95% CI −9% to 15%) (El Moussaoui et al., BMJ 2006). The trial was funded by a Dutch healthcare insurance board (grant OG99-038), GlaxoSmithKline supplied the capsules, and no competing interests were declared. A confidence interval that runs from −9% to 15% is wide, so the trial could not rule out a meaningful difference in either direction.

A second Dutch study looked at a different question: whether a stewardship programme could reduce broad-spectrum use without raising deaths. It is a cross-sectional, stepped-wedge, cluster-randomised non-inferiority trial in 12 Dutch hospitals, with 4,084 patients analysed. Broad-spectrum days fell from 6.5 to 4.8 per patient, an absolute reduction of 1.7 days (95% CI −2.4 to −1.1). Crude 90-day mortality was 10.9% in the control period and 10.8% in the intervention period, an adjusted risk difference of 0.4% (90% CI −2.7 to 2.4), which indicates non-inferiority (CAP-PACT, Lancet Infectious Diseases 2022). The trial declares no funding, and one author reports grants and personal fees from Pfizer and MSD. This is good evidence that shorter, narrower prescribing is possible in a hospital programme. It is not a trial that tells an individual how many days to take.

NICE NG250 (2025) gives the adult rule we could open. It says to stop antibiotic treatment for adults with community-acquired pneumonia after 5 days unless specific exceptions apply, and its table gives amoxicillin 500 mg three times a day for 5 days for low-severity disease (NICE NG250, recs 1.6.2 and 1.6.3). The Dutch trial tested 3 days in total against 8, so it does not test the guideline's 5-day rule directly. The ATS/IDSA 2019 guideline was supported by the American Thoracic Society and the Infectious Diseases Society of America (Metlay et al., AJRCCM 2019). We did not check its duration recommendation text.

Do corticosteroids help?

Steroids are the most contested question in severe pneumonia. The CAPE COD trial was a double-blind, placebo-controlled trial in adults admitted to the ICU with severe community-acquired pneumonia, conducted in France. Patients received intravenous hydrocortisone 200 mg daily for 4 or 7 days, tapered to a total of 8 or 14 days, or placebo. The trial was stopped after the second planned interim analysis: 800 patients were randomised and 795 analysed. Death by day 28 occurred in 25 of 400 patients (6.2%) on hydrocortisone and 47 of 395 (11.9%) on placebo (absolute difference −5.6 percentage points, 95% CI −9.6 to −1.7; P=0.006). The sponsor was University Hospital, Tours, and the NEJM abstract states it was funded by the French Ministry of Health (Dequin et al., NEJM 2023). The trial registry lists 952 participants as enrolled (NCT02517489). We could not reconcile that figure with the 800 randomised and 795 analysed in the paper.

The 2024 meta-analysis pooled 10 randomised trials with 1,962 patients. It found lower all-cause mortality with corticosteroids overall (risk ratio 0.70, 95% CI 0.54 to 0.90; I² 0%). Hydrocortisone alone was associated with about half the mortality (risk ratio 0.48, 95% CI 0.32 to 0.72), while dexamethasone, methylprednisolone and prednisolone were not associated with an improvement (See et al., BMJ Open Respiratory Research 2024). The review declares no competing interests. Because the hydrocortisone result rests on a few trials, we grade it moderate rather than strong. NICE NG250 advises considering a corticosteroid for 4 to 7 days in adults with high-severity pneumonia in hospital, and suggests intravenous hydrocortisone as the first choice (NICE NG250, recs 1.8.1 and 1.8.2).

Does pneumococcal vaccination prevent pneumonia?

The CAPiTA trial is the largest vaccine trial in this area. It randomised 84,496 adults aged 65 and over to the 13-valent pneumococcal conjugate vaccine (PCV13) or placebo. The primary result was 45.6% efficacy against vaccine-type pneumococcal pneumonia (95.2% CI 21.8 to 62.5). There were 75.0% efficacy against vaccine-type invasive pneumococcal disease (95% CI 41.4 to 90.8), with 7 cases in the vaccine group and 28 in the placebo group (Bonten et al., NEJM 2015). The abstract states the trial was funded by Pfizer, and several authors have Pfizer Vaccine Clinical Research affiliations.

The Cochrane review of pneumococcal polysaccharide vaccine is more cautious. It supports the vaccine for invasive pneumococcal disease in adults (randomised trials OR 0.26, 95% CI 0.14 to 0.45), but finds no clear benefit for all-cause pneumonia in high-income general populations (OR 0.71, 95% CI 0.45 to 1.12) or for mortality (OR 0.90, 95% CI 0.74 to 1.09). In low-income countries it found pneumonia reduced (OR 0.54, 95% CI 0.43 to 0.67) (Moberley et al., Cochrane 2013). The review's funding text was not in the record we opened.

Does influenza vaccination prevent pneumonia?

The Cochrane review of influenza vaccines in older adults found that vaccinated people had 0.42 times the risk of influenza (95% CI 0.27 to 0.66; low certainty). It reported one study in which no cases of pneumonia occurred, and it does not show a clear reduction in pneumonia (Demicheli et al., Cochrane 2018). The healthy-adult review found a risk ratio of 0.96 for hospitalisation (95% CI 0.85 to 1.08; 11,924 participants; low certainty), and 15 of its included trials were industry-funded, about 29% (Demicheli et al., Cochrane 2018). The evidence supports influenza vaccination for reducing influenza, not pneumonia specifically.

Does the RSV vaccine help?

A trial of a prefusion F RSV vaccine in 24,966 participants found 82.6% efficacy against RSV-related lower respiratory tract disease (96.95% CI 57.9 to 94.1). The NEJM abstract states it was funded by GlaxoSmithKline Biologicals (Papi et al., NEJM 2023). The result is strong for the outcome measured, but it measures RSV disease, not pneumonia from all causes, and it comes from the maker's own trial.

Do vitamin D or vitamin C help?

The largest pooled study of vitamin D (individual-participant data pooled from multiple trial datasets) found that supplementation reduced acute respiratory tract infection overall (adjusted odds ratio 0.88, 95% CI 0.81 to 0.96). The protection was seen with daily or weekly dosing (aOR 0.81, 95% CI 0.72 to 0.91) and not with one or more bolus doses (aOR 0.97, 95% CI 0.86 to 1.10). Pneumonia was not reported as a separate outcome (Martineau et al., BMJ 2017). That is the basis for our "insufficient" grade for pneumonia. The study was funded by Medical Research Council, NIHR (HTA) and NHLBI grants.

The Cochrane review of vitamin C found three prophylaxis trials with 37 pneumonia cases among 2,335 people. The authors concluded that the evidence is too weak to advocate prophylaxis in the general population (Hemilä & Louhiala 2013). We did not verify the detailed trial populations or the treatment-trial results in the full text, so we rely on the authors' overall conclusion.

Do antibiotic choices differ?

The newer lefamulin trials give a direct comparison with moxifloxacin, but the data we could open are secondary analyses. In patients with a baseline pathogen, early clinical response was 89.3% for lefamulin and 93.0% for moxifloxacin, and no confidence interval appears in the abstract (LEAP secondary analysis, J Glob Antimicrob Resist 2022). The authors are Nabriva Therapeutics employees or stockholders, and the company's own analysts ran the pooled analysis. We could not open the primary LEAP reports, so we cannot tell from our sources whether the trials were non-inferior by their own pre-specified margins.

Risks and complications

Aspiration pneumonia

Aspiration pneumonia mostly affects debilitated patients with dysphagia, and it often presents as community-acquired pneumonia. The main treatable factor is dysphagia, so swallowing assessment matters as much as antibiotics (Marik 2011). We did not find a trial in our search that settles which antibiotic is best for aspiration.

Antibiotic side effects and resistance

Antibiotic treatment carries its own risks, including effects on the gut and on antibiotic resistance. The stewardship trial shows that shorter, narrower prescribing reduced broad-spectrum use without a rise in 90-day mortality in its setting (CAP-PACT 2022). We did not open a source that quantifies these risks for the regimens discussed here, so we give no figures for them.

Vaccine side effects

We did not verify a source for vaccine safety figures in this review, so none are given here. Check the product information and the current national schedule before vaccination.

Who is at higher risk

• Older adults and people with heart or long-term lung disease: the NHS lists both as higher-risk groups for serious pneumonia (NHS). CAPiTA and the RSV trial are the strongest vaccine evidence in these age groups (Bonten 2015; Papi 2023).
• People with swallowing difficulty: dysphagia is the main underlying factor in aspiration pneumonia (Marik 2011).
• People who are not improving on antibiotics: the NHS lists this as a reason to seek review (NHS).
• Babies and young children: the NHS lists them as higher-risk, but this article covers adults, and we did not review paediatric evidence.

Trial doses, durations and vaccine schedules

These are the durations and doses reported in the trials and guidance we opened. They are not recommendations for any individual, and treatment decisions belong to a clinician.

Product quality and funding notes

• The trials of individual vaccine products used the maker's own vaccine, so the efficacy numbers apply to those products and schedules.
• The lefamulin data come from a maker-linked programme (LEAP 2022), so product-specific claims should be read with that in mind.

Follow the money: who makes it and who funded the evidence

Who makes the products

• Pfizer sponsored CAPiTA, the trial of the 13-valent pneumococcal conjugate vaccine (Bonten 2015). We did not verify Pfizer's headquarters or ownership in this review.
• GlaxoSmithKline Biologicals funded the RSV prefusion F vaccine trial in older adults (Papi 2023).
• Nabriva Therapeutics employed or was owned by the authors of the pooled LEAP lefamulin analysis (LEAP 2022). We did not verify the company's ownership.
• Vitamin D and vitamin C products are sold by many companies. We did not identify a single funder of the vitamin D or vitamin C evidence that we opened, beyond the public grants listed for the vitamin D review.

Who funded the trials and reviews

• CAPE COD: the registry lists University Hospital, Tours as lead sponsor (NCT02517489). The NEJM abstract states the trial was funded by the French Ministry of Health (Dequin 2023). We did not open the full paper.
• CAPiTA: funded by Pfizer, with several authors Pfizer-affiliated (Bonten 2015).
• CAP-PACT: funding "None" (CAP-PACT 2022); one author reports Pfizer and MSD ties.
• Cochrane pneumococcal review (2013): funding text not in the record we opened (PubMed conflict statement "None known").
• Cochrane influenza reviews (2018): funding not in the record; 29% of included healthy-adult trials were industry-funded (Demicheli 2018).
• Vitamin D individual-participant meta-analysis (2017): Medical Research Council, NIHR and NHLBI grants (Martineau 2017).
• Corticosteroid meta-analysis (2024): competing interests none declared; no grant listed (See 2024).

Documented integrity events

In this review we did not find documented regulatory bans, warning letters or recalls for the vaccines, antibiotics or corticosteroids discussed. We did not search every regulator's enforcement database, so treat this as a gap rather than a clean record.

Industry funding of antibiotic trials

The clearest documented example in this review is the lefamulin programme. The pooled LEAP analysis was written by Nabriva Therapeutics employees and stockholders, and the company contracted testing work for the trials (LEAP 2022). That does not make the result wrong. It means the product's own maker shaped the trial programme, so the result should be weighed with the same caution as other maker-run trials.

Related research

• Asthma Prevention and Management: Evidence and Safety Guide
• Asthma Supplements: Nutritional Roles, Evidence Limits and Safety
• Dysphagia (difficulty swallowing): causes, tests, treatment and urgent signs
• Septic Cardiomyopathy: Sepsis-Induced Heart Dysfunction, Diagnosis and Care
• Vitamin D: D2 vs D3, Deficiency, Benefits and Safety
• Probiotics: Clinical Evidence, Strains, Doses and Safety
• C. difficile infection: treatment, recurrence and supplement evidence
• Pulmonary Embolism: Emergency Symptoms, Diagnosis, Treatment and Recovery

Frequently asked questions

Sources and funding notes

What we could not verify. The full CAPE COD paper was not opened; we verified its NEJM abstract, which gives the funder, the randomised and analysed numbers, and the mortality figures. The trial registry lists 952 participants as enrolled, while the paper reports 800 randomised and 795 analysed. We could not reconcile the two. The funding statement of the 2013 Cochrane pneumococcal review could not be opened; its PubMed record lists no conflicts. The ATS/IDSA 2019 guideline is supported by the ATS and IDSA; we did not open its disclosure text or its duration recommendations. We could not locate a CDC/ACIP 2014 vaccine summary, so no figures from it are used. Zinc, probiotic and other supplement trials in adult pneumonia were not reviewed in full.

1. Lim WS et al. Defining community acquired pneumonia severity on presentation to hospital (Thorax 2003): CURB-65 derivation; no grant listed in the PubMed record.
2. El Moussaoui et al. Effectiveness of discontinuing antibiotic treatment after three days versus eight days (BMJ 2006): funded by a Dutch healthcare insurance board (grant OG99-038); GlaxoSmithKline supplied capsules; no competing interests declared.
3. Schweitzer VA et al. CAP-PACT (Lancet Infectious Diseases 2022): funding "None" (abstract); author declarations include Pfizer and MSD grants and fees.
4. NCT02517489, CAPE COD registry entry: lead sponsor University Hospital, Tours; enrolment recorded as 952 (actual).
5. Dequin PF et al. Hydrocortisone in Severe Community-Acquired Pneumonia (NEJM 2023; PMID 36942789): abstract opened; funded by the French Ministry of Health; 800 randomised, 795 analysed; 25/400 vs 47/395 deaths at day 28.
6. See XY et al. Impact of different corticosteroids on severe community-acquired pneumonia (BMJ Open Respiratory Research 2024; PMID 38262670): meta-analysis of 10 RCTs, 1,962 patients; competing interests none declared; no grant listed.
7. Bonten MJ et al. Polysaccharide conjugate vaccine against pneumococcal pneumonia in adults (NEJM 2015; PMID 25785969): funded by Pfizer (abstract); Pfizer-affiliated authors.
8. Moberley S et al. Vaccines for preventing pneumococcal infection in adults (Cochrane 2013): funding text not in the record opened; conflict statement "None known".
9. Demicheli V et al. Vaccines for preventing influenza in the elderly (Cochrane 2018): influenza vaccine review; funding text not in the record; one author reports an NIHR grant and royalties.
10. Demicheli V et al. Vaccines for preventing influenza in healthy adults (Cochrane 2018): 15 of the included RCTs industry-funded (29%).
11. Papi A et al. Respiratory syncytial virus prefusion F protein vaccine in older adults (NEJM 2023): funded by GlaxoSmithKline Biologicals (abstract).
12. Martineau AR et al. Vitamin D for the management of acute respiratory tract infection: individual participant data meta-analysis (BMJ 2017): Medical Research Council, NIHR (HTA) and NHLBI grants.
13. Hemilä H & Louhiala P. Vitamin C for preventing and treating pneumonia (Cochrane 2013): funding text not in the record opened; no conflicts listed.
14. LEAP lefamulin pooled microbiological analysis (J Glob Antimicrob Resist 2022; PMID 34788694): authors are Nabriva Therapeutics employees or stockholders (conflict statement); no grant listed.
15. Paukner et al. Lefamulin in patients with community-acquired bacterial pneumonia caused by atypical respiratory pathogens (Antibiotics 2021; PMID 34943700): no grant listed; authors are Nabriva Therapeutics employees or stockholders.
16. Metlay JP et al. ATS/IDSA guideline on community-acquired pneumonia in adults (AJRCCM 2019): supported by the American Thoracic Society and the Infectious Diseases Society of America; disclosure text not opened.
17. Marik PE. Pulmonary aspiration syndromes (Current Opinion in Pulmonary Medicine 2011): review of aspiration syndromes and dysphagia.
18. NHS. Pneumonia: warning signs and who is at higher risk: publicly funded UK health service guidance.
19. NICE NG250. Pneumonia: diagnosis and management (published 2 September 2025): publicly funded UK guideline; recommendations opened (recs 1.2.2, 1.2.8, 1.4, 1.6.2–1.6.3, 1.8.1–1.8.2).

Educational research reviewed 9 October 2026. This article is not medical advice; talk to a qualified clinician or pharmacist before starting, stopping or combining treatments.