Pneumonia

This entry was first published in November 2019.

2.56 million people died from pneumonia in 2017. Almost a third of all victims were children younger than 5 years. Here in this research entry we look at who is suffering from pneumonia and why – and what can we do to reduce the number of people dying from it.

Pneumonia is an infection of the tiny air sacs of the lungs, called alveoli. In a person with pneumonia the alveoli are filled with pus and fluid, which makes breathing painful and reduces the oxygen intake. Pneumonia is caused by a number of infectious agents, including viruses, bacteria and fungi. 

Estimates that refer to pneumonia might also include cases of other lower respiratory diseases

Ideally, pneumonia would always be diagnosed by a physician using radiological imaging and by determining the causative agent. However, because such diagnosis requires a lot of resources, it is often not possible to do.

In the research literature the terms ‘clinical pneumonia’ or ‘WHO-pneumonia’ refers to diagnoses based on symptoms (most importantly, fast breathing and coughing). Symptoms-based definition inevitably means that diseases with similar symptoms may be included.

As a consequence the terms pneumonia and lower respiratory infections (LRIs) are often used interchangeably. The Institute for Health Metrics and Evaluation (IHME), for example, provides mortality data on LRIs, which they define as pneumonia caused by a range of different pathogens, though they also include bronchiolitis in this category.1 2 While cases of bronchiolitis are quite common they are generally not fatal, therefore, it is reasonable to assume that most of IHME estimates for the number of deaths do mostly refer to cases of pneumonia. 

Burden of pneumonia

Number of people dying from pneumonia today by age

In the visualization here we see the global number of deaths from pneumonia3 by age group.

The number of children dying from pneumonia has decreased substantially over the past three decades. In 1990, more than two million children died from pneumonia every year: it was the leading cause of death in children, accounting for 20% of all childhood deaths. By 2017, this number had fallen by almost two-thirds.

Improvements in the major risk factors such as childhood wasting, air pollution, and poor sanitation as well as increased availability of treatments such as pneumococcal vaccines and antibiotics have all contributed to this decline.

As the world population grew and aged, the number of deaths of people who were 70 years and older increased in the same time span.

Pneumonia mortality rates by age

The chart shows the annual number of deaths from pneumonia per 100,000 people in different age groups.

There has been a 3-fold reduction in child mortality due to pneumonia over the last three decades. 363 children out of every 100,000 died due to pneumonia in 1990, until 2017 that number has fallen to 119.

The mortality rates among other age groups have remained largely the same. The highest pneumonia mortality rates in 2017 were among people aged 70 and older. 261 out of 100,000 people died in this age group due to pneumonia. That’s a 9% decrease in mortality rates over the past 3 decades.4

While the death rate for old people fell slightly, the number of deaths of people who are 70 years and older increased. This is because the number of people who reached the age of 70 increased very strongly globally. 1.13 million, who died from pneumonia where in this age group.

Where do people die from pneumonia?

Pneumonia death rates – all ages

In the map we see the death rate from pneumonia expressed as the number of deaths due to pneumonia per year per 100,000 individuals.

We can see that most deaths from pneumonia occur in Sub-Saharan Africa as well as in Southeast-Asia. In Southeast-Asia, Philippines have particularly high pneumonia mortality rates; pneumonia is the second leading cause of death in both under-5-year-old and older than 70-year-old populations in this country.

These rates have been age-standardized, which tells us the death rate for each country and each point in time as if the age structure of a population. This therefore allows us to make across comparisons across countries and through time that are not affected by differences in the age-structure between countries and changes of the age-structure over time.

Where do children die from pneumonia

The map shows the number of child deaths due to pneumonia per 100,000 children per year.

As the map shows, children are most likely to die from pneumonia across Sub-Saharan Africa and South Asia. Just 5 countries — India, Nigeria, Pakistan, the Democratic Republic of Congo, and Ethiopia – accounted for more than half of all deaths from childhood pneumonia in 2017. 

In a 2018 comment in the journal The Lancet, Kevin Watkins and Devi Sridhar called pneumonia “the ultimate disease of poverty”.5 There is a strong correlation between a country’s income and the child mortality rate from pneumonia.

Pneumonia is not a disease that easily spreads across borders, its transmission is generally restricted to local communities and it can be controlled if basic health measures are available. The disease is therefore most common in places where healthcare infrastructure is lacking and people are least able to afford the treatment.6

What are the biggest risks for developing pneumonia?

Why are children dying from pneumonia?

To understand how we can reduce the number of children dying from pneumonia we need to understand both prevention and treatment. 

In the chart we show the number of child deaths from pneumonia which are attributed to various risk factors. 

Undernutrition is the major contributor to pneumonia mortality

Here we see that childhood undernutrition, especially so called ‘child wasting’ (children who have a weight too low for their height), is the biggest risk factor for pneumonia in children.7 It contributed to 53% of pneumonia deaths in 2017. Without sufficient energy intake the body cannot cope with increased energy demands required to fight off the infection.

A literature review of pneumonia in malnourished children by Mohammod Jobayer Chisti and colleagues found that undernourished children are between two and four times more likely to be admitted to hospital due to pneumonia and up to 15 times more likely to die from it.8

Air pollution and second-hand smoke increase the risk of getting pneumonia 

Indoor air pollution was the risk factor that is estimated to have lead to 29% of pneumonia deaths in 2017. Outdoor air pollution was responsible for another 18% of all deaths.

Studies have shown that high indoor air pollution in households can double the chances a child develops pneumonia and makes recovery less successful.9 One of the underlying reasons for why this is the case is that the small polluting particles impair the immune system’s ability to fight and clear the infection.

Laura Jones et al. (2011) reviewed studies which assessed the impact of secondhand smoke on children, and concluded that children who live in households with smoking parents are more likely to acquire pneumonia as well as other respiratory illnesses. A Global Burden of Disease study by Mattias Öberg et al. has estimated that in 2004, globally around 40% of children lived in households where at least one close relative smoked.10 The data shown here suggests that the exposure to secondhand smoke led to 61,000 deaths among children under 5 from lower respiratory diseases in 2017.

The risk of pneumonia is higher for children with HIV

Exposure to other pathogens such as measles and HIV also increases the risk of pneumonia in children.

When children who are infected with HIV develop AIDS – which weakens their immune system – their chances of dying from pneumonia increase significantly. A study by Evropi Theodoratou et al., published in Lancet Infectious Diseases, found that children with HIV have a seven times greater risk of dying from pneumonia compared to those without it.11

The same study also showed that the proportion of child deaths from pneumonia that can be attributed to HIV varies widely between countries: in 2010 only 1% of all child deaths from pneumonia in India could be directly attributed to HIV, compared to 64% in Swaziland and 62% in Lesotho. In Africa, a total of 3% of cases and 17% of all childhood deaths from pneumonia was attributable to HIV. These regional differences are important to know so that interventions that can save most lives can be prioritized. 

Overcrowding facilitates pneumonia transmission 

Pneumonia is not an easily transmittable disease, it requires close contact for the pathogens to be transmitted to another person via air droplets. Therefore overcrowding – too many people living in one space – also increases the risks of pneumonia. This is yet another reason why pneumonia is a disease of poverty: in 2015, 47% of children in low and middle-income countries were living in overcrowded households.12

Despite progress against it, more than 800,000 children still die from pneumonia each year. We know where children are dying, and the factors that make them vulnerable to the disease. The key question is how we continue to make progress against it.

Pneumonia risk factors for people aged 70 and older

The risk factors for developing pneumonia in people aged 70 and older are similar to the risk factors that lead to pneumonia in children.

Outdoor air pollution – small particulate matter air pollution – is the risk factor that lead to most deaths. In 2017 it lead to more than 300,000 deaths from pneumonia of older people.

Smoking and exposure to secondhand smoke have contributed to 150,000 and 73,000 deaths from pneumonia in this age group, respectively.

How can we reduce the number of people dying from pneumonia?

When we understand what risks can lead to pneumonia, we can find ways to reduce them. Furthermore, because a number of risks factors for pneumonia overlap with risk factors for other diseases, especially diarrheal diseases, interventions that target pneumonia have the additional benefit of helping to limit other diseases and saving more lives.

Vaccines against pneumonia

There are several versions of pneumococcal conjugate vaccine (PCV), which target different serotypes of S. pneumoniae — the bacterium responsible for most cases of pneumonia.

The PCV vaccine is given to children younger than 24 months. According to a study by Cheryl Cohen et al. (2017), PVC13 – the currently recommended PCV vaccine version – has 85% effectiveness against invasive infections caused by the specific strains the pneumococcal strains included in the vaccine formulation.13 

It has been estimated that if PCV13 coverage in low income countries would reach the coverage of the DTP3 vaccine, then PCV13 could prevent 399,000 child deaths and 54.6 million pneumonia episodes annually when compared with a world in which no pneumococcal vaccination was available.14 India – which has the highest number of child deaths from pneumonia – only introduced PCV13 in 2017 and the coverage is still very low — clearly the pneumococcal vaccine still has a lot of potential.15

Another vaccine widely used to protect children against both pneumonia is the Hib vaccine.

Hib immunizes children against Haemophilus influenzae type b, a leading cause of meningitis in children that is also responsible for around 2% of pneumonia deaths of children younger than five years. In 2015 there were around 0.9 million cases of Hib-related pneumonia globally. The Hib immunization provides around 70% protection against Hib-related pneumonia and 84% protection against meningitis in children.16

Promoting breastfeeding

Encouraging mothers to breastfeed during the first 6 months of a child’s life has a positive impact on reducing child undernutrition, which in turn protects from infectious diseases such as pneumonia.

According to Laura Lamberti et al. (2013), pneumonia mortality of children in developing countries who are not breastfed in the first 5 months of their lives is 15 times greater than those who exclusively received their mother’s milk.17 As the map shows, the number of infants who are exclusively breast fed is still low in many countries. Globally, an estimated 41% of infants were exclusively breastfed in 2017.18

Reducing air pollution

There has been a significant progress in reducing air pollution levels in recent decades, particularly of indoor air pollution.

Death rates from indoor air pollution fell as a result of improved access to cleaner fuels for heating and cooking. But there is still much progress to be made, especially in Sub-Saharan Africa, where in most countries less than 10% of households have access to clean fuels for cooking. And, whilst progress has been made against indoor air pollution, high levels of outdoor pollution remain a problem across many countries. Reducing air pollution levels would have many other benefits: it would not only reduce the number of cases of pneumonia but also limit the incidence of asthma in children for example.19

Access to healthcare and treatment

A child with a suspected case of pneumonia – with symptoms of difficulty in breathing and coughing – should be taken to a healthcare provider so that the correct and immediate treatment can be provided. Delay in seeking treatment can increase the chances of a child dying.20 However, as the map shows, seeking healthcare is still not as common as it should be. Globally, less than two-thirds of children with symptoms of pneumonia were taken to a healthcare provider in 2016. This figure is even lower in places where healthcare is most needed — just 47% in Sub-Saharan Africa.21 

As the map shows, the share of children with symptoms of pneumonia that are take to a health provider is still low in many countries.

Access to antibiotic treatment

Given that most cases of pneumonia are of bacterial origin, antibiotics are the general course of treatment.

Due to the lack of resources, in places where pneumonia cases are most common, a quick diagnosis for the cause of disease is not always possible. Given the potential high risk of death from untreated pneumonia, the World Health Organisation (WHO) recommends antibiotic treatment depending on the disease symptoms and its severity before the cause of disease is known. Amoxicillin, ampicillin and gentamicin are the most commonly used antibiotics to treat pneumonia.22 23

Oxygen therapy

During pneumonia, alveoli in the lungs get filled with pus and fluid, which prevents oxygen from being transferred to the blood. Consequently, a condition known as hypoxaemia – a lack of oxygen – can develop.

When a child with pneumonia develops hypoxaemia the risk of dying increases five-fold.24 Treatment with oxygen therapy (supplying oxygen-enriched air to the patient)25 is one way to mitigate hypoxaemia.26

A study from Papua New Guinea has shown that oxygen therapy can reduce the risk of death from severe pneumonia by 35%. However, the need for a specialist equipment to diagnose and treat hypoxaemia still poses a substantial barrier in low-resource settings. Since 2017, the WHO includes oxygen in its List of Essential Medicines.27 Improved access to oxygen could save the lives of 120,000 children annually.28  

Pneumococcal vaccines

There are a number of ways we could reduce the number of children dying from pneumonia, including eliminating the major risk factors such as undernutrition and air pollution, and providing better access to treatment.

But we have another highly effective intervention: a vaccine against the major pathogen responsible for pneumonia in children.

Streptococcus pneumoniae is the leading cause of pneumonia in children under 5 — it was responsible for 52% of all fatal pneumonia cases in children in 2016.29 Pneumococcal vaccines are vaccines that target S. pneumoniae bacteria. Here we look at their effectiveness and how we can maximise the number of children they save.

The coverage of pneumococcal vaccines is still low

Since the World Health Organisation (WHO) started recommending including pneumococcal vaccines in national immunisation programmes for children in 2007, there has been a progressive increase in the number of countries using the vaccine. You can see the uptake in the vaccine across the world using the ‘play’ button on the map below.

But the coverage of pneumococcal vaccines is still low in many countries. In India and Nigeria – the two countries with the greatest number of childhood deaths from pneumonia in 2017 – only 44% and 58% of one-year-olds are vaccinated, respectively. 

In 2018, less than half (47%) of one-year-olds in the world received the full course of pneumococcal vaccination. This means that 55 million children who could be protected by the vaccine are still not vaccinated against it — an appallingly high number for a vaccine that not only protects from pneumonia, the leading cause of childhood death, but also a range of other diseases (as discussed below).30

How do pneumococcal vaccines work?

Streptococcus pneumonia, often simply referred to as pneumococcus, is a bacterium that is often found in the upper respiratory tract of healthy people. Generally, the bacterium is harmless or causes milder illnesses such as bronchitis, sinusitis, and ear infections. Pneumococcal vaccines are effective against these milder illnesses as well, but importantly also protects from what is called pneumococcal invasive disease (PID). PID occurs when the pneumococcus moves from colonizing the upper respiratory tract to colonizing sites that are normally sterile, such as blood, cerebrospinal fluid or pleural cavity (fluid-filled space surrounding the lungs).31 Bacterial invasion leads to life-threatening diseases such as sepsis, meningitis and severe pneumonia. 

There are two types of pneumococcal vaccines available: conjugated polysaccharide pneumococcal vaccine (PCV) and non-conjugated polysaccharide pneumococcal vaccine (PPSV). Both vaccines are designed to elicit immune responses against multiple serotypes of pneumococcus, which are defined by the different immune responses to the sugars found on the bacterial surface.32 To be broadly effective, the vaccines need to protect against a certain number of these pneumococcal serotypes, but it is not necessary to include all possible serotypes because only a limited subset is responsible for 70%-80% of invasive pneumococcal disease.33 However, as we’ll discuss later, this variety of different pneumococcal serotypes is important to keep in mind because as vaccine coverage increases we may see a replacement of the vaccine-included serotypes with the less dominant ones, which will mean new vaccine versions will be required.  

While there are two types of pneumococcal vaccines available, for children under two years old only the conjugated (i.e. PCV) vaccines are recommended because the non-conjugated versions (i.e. PPSV) are not effective at such a young age.34 

How effective are pneumococcal vaccines?

In clinical trials PCV has shown 80% efficacy in reducing invasive pneumococcal disease caused by the bacterial serotypes included in the vaccine formulation. Vaccinated children are 27% less likely to be diagnosed with pneumonia and 11% less likely to die from it.35

Several studies have attempted to estimate how many lives PCV vaccination has saved and could possibly save. One Lancet study concluded that between 2000 and 2015, in 120 countries the number of childhood deaths caused by pneumococcus fell from 600,000 to 294,000 — a decline of 54%. Most of this decline was attributed to the PCV vaccines: over this period, it’s estimated these vaccines saved the lives of 250,000 children. The majority of these deaths would have been caused by pneumonia, but the vaccine also prevented deaths from pneumococcal meningitis and other diseases.36 

How many child deaths could be averted by pneumococcal vaccines?

The chart shows how estimates of the potential impact of the pneumococcal vaccine.

It is based on a recent study published in The Lancet Global Health journal, which calculated that if the PCV vaccine coverage would reach at least the levels of the vaccination against diphtheria, tetanus and pertussis (DTP3), the lives of 399,000 children under 5 could be saved.37 Additionally the researchers estimate that 54.6 million pneumonia episodes annually could be averted.

These number estimate the impact of the PCV vaccination relative to a world without that vaccine – since the vaccine is already used it means that some of these lives are already being saved by the PVC vaccination. However, in many countries PCV vaccination rates still fall far below the DTP3 rates, making clear that we still haven’t used the pneumococcal vaccine to its full potential.

What can we do to improve the coverage and effectiveness of  pneumococcal vaccines?

A continued increase in immunization coverage and the introduction of PCV vaccines into countries which don’t yet use them is important if we want to make use of the full potential of pneumococcal vaccines. 

PCV vaccines are amongst the most expensive vaccines in national immunisation programmes. The price ranges from $3.05 per dose in GAVI38 supported low-income countries to $169 in high-income countries such as the United States.39 For low-middle-income countries who are transitioning from GAVI support the increasing future costs of vaccination place a considerable strain on national healthcare budgets.40 

But given the high burden of pneumococcal diseases, even at high prices, PCV vaccines are considered to be cost-effective, with an estimated return of investment in low- and middle-income countries of around 3.41 

PCV vaccines include a limited subset of possible pneumococcal serotypes. The distribution of pneumococcal serotypes is known to vary between countries and PCV vaccines include the ones that are most common globally.

Which non-vaccine serotypes are most common in a particular country, may affect the potential for a particular vaccine’s impact. However, not all countries collect data on serotype distribution, and an assessment of the potential impact is therefore compromised.42 43 44 Notably, since the PCV vaccine was introduced, there has been a rise in pneumococcal invasive disease incidences caused by the less common serotypes. This suggests that, by reducing the prevalence of vaccine-included serotypes, the vaccine unintentionally provides space for non-vaccine serotypes, against which it works less well.45 This means that the vaccine’s effectiveness may decrease over time, if the serotype formulation of PCV is not continually reevaluated. In the future, new versions of pneumococcal vaccines may be needed that work better independently of the bacterial serotype. Such vaccines are already in development.46 47

Additional Information

What pathogens cause pneumonia?

Pneumonia is an infection of the lower respiratory tract that can be caused by multiple microbial pathogens. 

By far the most common cause of pneumonia in unvaccinated children is an infection by a bacterium called Streptococcus pneumoniae, simply referred to as pneumococcus. The Global Burden of Disease (GBD) study from 2018 has estimated that pneumococcus was responsible for 52% of fatal pneumonia cases in children in 2016.48 

Other pathogens which cause pneumonia in children are Haemophilus influenzae type b, respiratory syncytial virus (RSV), and the influenza virus. Each of these pathogens was responsible for less than 4% of lethal pneumonia cases in 2016.49 Despite being minor causes, it’s important to continue developing treatments against these pathogens; they will become increasingly important as vaccination coverage for the most common causes increases. According to a study by Katherine O’Brien et al. (2019), when children are routinely vaccinated with pneumococcal and Hib vaccines, as many as 62% of pneumonia cases are caused by viral pathogens such as RSV.50 

How is pneumonia acquired and transmitted?

Children can contract pneumonia in a number of ways. Pneumococcus and H. influenzae are bacteria that can be found in the upper respiratory tract of healthy individuals without any symptoms. Under circumstances when the conditions in the upper respiratory tract are compromised51 these normally benign bacteria may move to the lower respiratory tract where they lead to pneumonia.52

Pneumonia caused by bacterial and viral pathogens can be contagious and transmitted when a person coughs or sneezes. However, precautions such as sanitizing hands and surfaces, wearing a face mask if available and limiting close contact with a sick person can significantly limit the chances of transmission.