“In children and in healthy adults the outlook [of pneumonia] is good. In the debilitated, in drunkards and in the aged the chances are against recovery. So fatal is it in the latter class (i.e. the elderly) that it has been termed the natural end of the old man.”
William Osler, The Principles and Practice of Medicine, first edition, 1892
“Our study highlights the importance of preventing, looking for, and aggressively treating secondary bacterial pneumonia in critically ill patients with severe pneumonia, including those with COVID-19.”
Benjamin Singer, MD, pulmonologist, Northwestern University Feinberg School of Medicine
Pneumonia is an infection that affects one or both lungs. In the 19th century, the father of internal medicine, Sir William Osler, described pneumonia as “the old man’s friend” as it was a relatively painless way for old people to die.
Remarkable progress has been in the management of pneumonia since Osler’s time. Nonetheless, pulmonary infections remain a major cause of hospitalizations and deaths worldwide. In 2021, 41,000 people died of pneumonia in the U.S. alone, and globally over 2.5 million deaths were attributed to pneumonia.
In this week’s Germ Gems post, I highlight four of the causes of pneumonia—all of which are big killers but share one vulnerability feature: they can be prevented with vaccines. And I provide an update on pneumonia vaccines for adults.
What is pneumonia? Infections of the respiratory tract are commonly classified by their location as “upper respiratory infection” (URI) or “lower respiratory infection.” URIs are often referred to as “common colds.” The “common cold” is responsible for a great deal of human suffering (morbidity), but it’s rarely, if ever, fatal.
The lungs are located in the lower respiratory tract. When infection is located here it’s called pneumonia, a not uncommon cause of death.
Pneumonia can be caused by more than 30 different microbes, including bacteria, viruses, fungi, and parasites. The four most notorious causes of pneumonia, however, are the bacterium, Streptococcus pneumoniae, and three viruses: SARS-CoV-2 (the cause of COVID-19); influenza virus; and respiratory syncytial virus (RSV).
Regardless of the cause, the signs and symptoms of pneumonia are the same. They include:
Cough, which may produce greenish, yellow or even bloody mucus;
Fever, sweating and shaking chills;
Shortness of breath;
Rapid, shallow breathing;
Sharp or stabbing chest pain that gets worse when you breathe deeply or cough; and
Loss of appetite, low energy, and fatigue.
Anyone with the suspicion of pneumonia should immediately contact their health care provider.
Vaccines that prevent pneumonia in adults. In the past, the pneumococcal vaccine that provided protection against the bacterium S. pneumoniae was often billed as “the pneumonia shot.” That moniker is no longer useful as other vaccines are necessary (and available) to protect against three viral causes of pneumonia. To be adequately protected, you need ensure that you are up-to-date on all pneumonia shots.
Pneumococcal vaccine. The Centers for Disease Control and Prevention (CDC) recommends pneumococcal vaccine for adults 65 years or older (and for younger adults with certain risk conditions).
There are over 90 different serotypes of S. pneumoniae, each identified by the structure of the polysaccharide (a sugar) in the capsule that surrounds the gram-positive coccus. The capsule is a major virulence factor as it hides the bacterium from cells of the immune system called neutrophils. Vaccines aim to generate antibodies that attach to the capsule, thereby allowing neutrophils to recognize, engulf, and kill the bacterium.
The Food and Drug Administration (FDA) licensed two new pneumococcal conjugate vaccines (PCVs) for adults in 2021—PCV13 or Prevnar and PPSV23 or Pneumovax 23. Both are composed of polysaccharides from the capsules of different strains of S. pneumoniae (13 strains in the case of Prevnar and 23 in that of Pneumovax 23). If you’re uncertain whether you’ve been adequately vaccinated, query your healthcare provider.
COVID-19 vaccine. For the past two years, COVID-19 has been the third leading cause of death in the U.S. A study reported in 2023 from Northwestern University suggests that secondary bacterial pneumonia (that is, a bacterial infection on top of the viral infection) drives many COVID-19 deaths. This phenomenon is well recognized as a fatal complication of influenza, and we now know it also needs to be watched for in patients with COVID-19.
Currently, three COVID-19 vaccines are recommended in the U.S. Two are mRNA vaccines (Pfizer-BioNTech’s Comirnaty and Moderna’s Spikevax) and one is a protein subunit vaccine from Novavax. All of these vaccines target the spike protein on the virus’s surface, thereby blocking its ability to attach to ACE2 receptors and enter cells. But because immunity wanes over time, booster doses aimed at the main circulating viral mutants are recommended for all of these vaccines.
A summer uptick of COVID-19 infections is now underway with new variants emerging—the FLiRT variants predominate. (The trio KP.2, KP.3, and KP.1.1 is known collectively as the FLiRT variants.) For the upcoming 2024-2025 vaccine, the FDA asked manufacturers to develop a COVID-19 vaccine using the KP.2 strain for the formula. A recent study in Lancet, however, showed that subvariants like KP.2 have a capacity for increased immune evasion. Nonetheless, on June 27, 2024, the CDC recommended that everyone six months or older receive the updated COVID-19 vaccine shot this fall.
Seasonal flu vaccines. In the U.S., the flu season typically runs from September through April. The CDC recommends that everyone 6 months of age and older get an annual flu shot. The high-dose (HD) flu vaccine is recommended for adults aged 65 years an older. (Younger adults who are immunocompromised should also receive the HD vaccine.)
Hemagglutinin (HA) and Neuraminadase (N) are two key proteins on the surface of the influenza virus that play a role in the virus’s ability to enter cells. These surface proteins (called antigens) are the major targets of flu vaccines, and because seasonal mutations of these proteins occur every year, recommendations change regarding what viral strains are included in the seasonal flu vaccine.
Flu shots are designed to protect against the virus strains considered most likely to cause seasonal flu. For the 2024-2025 flu season, the FDA recommends a trivalent vaccine that targets three influenza virus strains: A(H1N1), A(H3N2) and B/Victorian lineage.
RSV vaccine. In the U.S., the RSV season typically runs from October through March, but can start as early as September and last later into the spring. Historically, RSV infection was recognized as a serious problem in the pediatric population. But RSV is also a leading cause of respiratory hospitalizations and deaths in older adults, approaching a level of concern similar to that with the flu.
The RSV vaccines work by targeting the RSV fusion protein that plays a crucial role in the virus’s ability to enter cells. The vaccine is a single dose and appears to provide some protection for at least two RSV seasons.
The CDC recommends vaccination against RSV for all adults over age 75 and high-risk adults between 60 and 74. And despite identification of increased rates of Guillain-Barre syndrome (GBS) among older adults following RSV vaccination, the CDC suggests the benefits outweigh the risk. (Both the CDC and the FDA are conducting active safety evaluations for GBS and other adverse events after RSV vaccination.)
Protection is there; use it. In the late 1800s, when Osler published his landmark textbook, The Principles and Practice of Medicine, pneumonia wasn’t only “the old man’s friend”; it was the leading cause of death worldwide. (Osler referred to pneumonia as the “Captain of the men of Death.”) A physician could do little to treat the disease and nothing to prevent it.
Now there are diagnostic tests for pneumonia, antibiotics to treat it, vaccines to prevent it, and vast improvements in the critical care of patients with the disease. Nonetheless, pneumonia still causes more than a million hospitalizations and more than 50,000 deaths each year in the U.S. (American Lung Association data).
If your old like I am, you can protect yourself from “the old man’s friend.” To do this, make sure that you are fully vaccinated against pneumonia. Get all four pneumonia shots.
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