Global Immunisation Today

• BCG (Tuberculosis): 87% in 2023.
• Hepatitis B (3rd dose): 83%, but the critical birth dose is only at 45%.
• Haemophilus influenzae type b (Hib, 3rd dose): 77% globally, but with significant regional differences.
• Pneumococcal conjugate vaccine (final dose): 65% globally.
• Rotavirus vaccine: 55% globally.
• HPV vaccine (first dose in girls): Increased from 20% in 2022 to 27% in 2023, showing growing but still low uptake for this cancer-preventing vaccine.
• Yellow Fever vaccine: 50% coverage in at-risk countries, well short of the recommended 80%.

Immunisation programs target a range of infectious diseases based on their prevalence and public health importance in each region. Core vaccines protect against diseases like Diphtheria, Tetanus, Pertussis, Measles, Mumps, Rubella, Polio, Tuberculosis, Hepatitis B,

Hib, Rotavirus, and Pneumococcal disease. Regionally, programs also target diseases like HPV, Yellow Fever, Japanese Encephalitis, Meningitis, Influenza, Cholera, Typhoid, and, of course, COVID-19.

A major concern currently is the resurgence of vaccine-preventable diseases (VPDs). This is most notably seen with measles. Estimated measles cases reached 10.3 million globally in 2023, a 20% increase from 2022. This upward trend is expected to continue, due to several factors, such as vaccine hesitancy, global funding issues and the rise of the anti-vax groups. In the past 12 months, 138 countries reported cases, with 61 experiencing large outbreaks – the highest number since 2019. Similar increases have been observed for pertussis (whooping cough) and yellow fever in various regions globally. These outbreaks are directly linked to reduced immunisation coverage, especially since the COVID-19 pandemic. Other underlying issues also play a part. An estimated 14.5 million children missed all routine vaccine doses in 2023, a significant increase from 2019. 

Measles is particularly concerning due to its extreme contagiousness. One infectious individual can infect 12-18 unvaccinated individuals when in close contact. The disease can lead to severe complications like pneumonia and encephalitis, and despite being preventable, 107,500 people died from measles in 2023. These were mostly children under 5. The measles vaccine is crucial because there is no specific treatment for the disease, and vaccination is highly effective in preventing severe illness and death. 

Other problems encountered globally include vaccine hesitancy, fuelled by misinformation, lack of trust, complacency, and specific unfounded concerns. The "anti-vax" movement actively promotes these perceived problems, often with the help of social media, contributing to lower vaccination rates, directly leading to outbreaks. Additionally, significant global funding cuts to international vaccine programs disrupt routine immunisation and surveillance, especially in lower-income countries. Humanitarian crises and local conflicts can put further strain on an already stressed health system, making vaccine delivery increasingly difficult. 

While the primary focus is on childhood immunisation, it's crucial to understand that Vaccine-preventable Diseases (VPDs) pose a substantial risk to older adults, a risk that is often underestimated. This vulnerability of the elderly stems from several factors:

• Immunosenescence: The natural age-related decline in the effectiveness of the immune system makes older adults more susceptible to infections and potentially less responsive to vaccines. Past immunity from an infection or a vaccine can also wane over time, increasing susceptibility.
  

• Comorbidities: Older adults often have other chronic health conditions (diabetes, heart or lung disease) that increase susceptibility to an infection, making it more difficult to fight off, and leading to a higher risk of severe complications.
  

• Waning Vaccine-Induced Immunity: Protection from some vaccines received earlier in life can decrease, necessitating booster doses.
  

• Community Transmission: When overall vaccination rates drop, VPDs circulate more widely, increasing the risk of exposure for everyone, including older adults. This emphasises the benefits of Herd Immunity.
  
  When older adults encounter VPDs, the effects can be significantly more severe than in younger, healthier individuals.  
  
  
  

  Here are some examples: 

• Influenza (Flu): While flu usually causes symptoms such as fever, cough, and fatigue, in older adults it can commonly lead to severe complications such as pneumonia (a leading cause of hospitalisation and death), exacerbation of chronic conditions (like heart failure or COPD), dehydration, and increased frailty. Hundreds of New Zealanders die from flu each year, mostly older adults.

• Pneumococcal Disease (Pneumonia, Meningitis, Sepsis): Symptoms vary by the type of infection. In the elderly, this disease often results in severe pneumonia requiring hospitalisation, potentially fatal bloodstream infections (sepsis), and meningitis, all of which may cause permanent brain damage or death. It's a leading cause of hospitalisation and death in older adults.

• Pertussis (Whooping Cough): Characterised by prolonged, severe coughing fits. Older adults might not have the classic "whoop" sound as the patient struggles to breathe, but present with a persistent cough. Complications include rib fractures from coughing, fainting (syncope) leading to falls and injuries, weight loss, and pneumonia. Undiagnosed but infectious pertussis in an older adult can be fatal if transmitted to an infant.

• Herpes Zoster (Shingles): Causes a painful rash. The most common complication in older adults is Postherpetic Neuralgia (PHN), a severe nerve pain that can last months or years and significantly impact the quality of life. The risk and severity of PHN increase with age. Shingles can also affect the eye (Ophthalmic Zoster), potentially causing vision loss.
  

• Tetanus: Causes muscle stiffness and painful spasms. Tetanus is more likely to be fatal in older people, with complications including respiratory failure, bone fractures from spasms, and heart complications.

• Diphtheria: Symptoms include a sore throat and the formation of a membrane that can block the airway. In the elderly, this can lead to severe airway obstruction, inflammation of the heart muscle (myocarditis) potentially causing heart failure and death, and nerve damage.

• Measles: While often a childhood disease, if immunity has waned or is absent, older adults are at risk of severe complications, including pneumonia, encephalitis, exacerbation of chronic conditions, and the rare but fatal delayed complication Subacute Sclerosing Panencephalitis (SSPE).
  
  

  Beyond the individual suffering, increased VPDs among older adults will significantly strain healthcare systems. They often require more intensive care, leading to longer hospital stays and higher healthcare costs. Outbreaks divert resources, and severe infections can cause a decline in the independence of the individual, potentially requiring long-term care.

  
  

  
  

  
  

The state of immunisation globally is precarious. While decades of progress have protected billions, factors such as falling vaccine coverage globally, the spread of misinformation, and funding shortages threaten these gains. The resurgence of VPDs such as measles is a stark reminder of how fragile our collective immunity can be. For everyone in healthcare, understanding these issues is vital. It's a call to action to champion evidence-based information, build trust in medical science, and advocate for sustained investment in immunisation programs for allages. Only through a strong, joint effort can we ensure that immunisation continues to protect both individuals and communities, from the youngest to the oldest, against infectious disease threats.