Immunisation is one of the most successful public health interventions but progress in the last two years has stalled or even reversed. COVID-19 and the threat of future pandemics have and will continue to strain even the most resilient health systems, so moving forward, strong immunisation programmes will be necessary to protect populations against vaccine-preventable diseases.
by Dr Aileen Dualan
Immunisation is one of the most successful public health interventions1 and there is no doubt that vaccines are critical to the prevention and control of infectious diseases. However, progress in the last two years has stalled or even reversed, with a decline in global coverage of haemophilus influenzae type B (HiB), hepatitis B, human papillomavirus (HPV), meningitis A, measles, mumps, pneumococcal diseases, polio, rotaviruses, rubella, tetanus, and yellow fever from 86 per cent in 2019 to 83 per cent in 2020.1
It is also estimated that more than 117 million children2 were at risk of missing out on measles vaccines during the height of the COVID-19 pandemic. COVID-19 and the threat of future pandemics have and will continue to strain even the most resilient health systems, but it has also reminded us of the power of vaccines to fight disease and save lives. As we move towards endemic living with COVID-19 in the new normal, strong immunisation programmes will be necessary to protect populations against vaccine-preventable diseases such as measles, which has increased by 79 per cent in the first two months of 2022 globally,3 as well as respiratory diseases such as diphtheria and rubella.
An Uptick of Infectious and Respiratory Viruses
In the last two years, COVID-19 measures such as social distancing and travel restrictions reduced4 the spread of infectious and respiratory diseases.5 There was a decline in infectious diseases such as measles by more than 80 per cent.6 In the Asia-Pacific, studies conducted in Hong Kong,7 Singapore,8 and Taiwan9 found a decline in pneumococcal diseases during the COVID-19 pandemic.
However, as more countries move towards endemic living with COVID-19 and public health measures such as social distancing and mask-wearing are rolled back, we are seeing a rise in infectious diseases such as measles and respiratory diseases including pneumococcal disease, respiratory syncytial virus (RSV), and seasonal flu. The World Health Organization (WHO) and the United Nations International Children’s Emergency Fund (UNICEF)3 reported an increase in measles cases in January and February 2022, which is a worrying sign of a heightened risk for the spread of vaccine-preventable diseases and could trigger larger outbreaks, particularly of measles affecting millions of children.
As for respiratory diseases, Australia10 experienced an increase in the overall frequency of RSV infections in children aged 2 to 4 years and in the peak case counts of RSV infections and RSV-coded hospitalisations for some age groups when interventions were relaxed. Outside of Asia, Germany11 and Switzerland12 are also experiencing a re-emergence of pneumococcal diseases following the easing of public health measures.
Why the Return of Infectious and Respiratory Viruses Is a Cause for Concern in the Asia-Pacific
An uptick in infectious viruses such as measles and the potential return of the measles outbreak could make one more vulnerable to respiratory viruses such as pneumonia. For this reason, the re-emergence of infectious and respiratory viruses needs to be closely monitored.
A regional study13 conducted in the Asia-Pacific found that pneumococcal diseases lead to high morbidity and mortality rates. Adult mortality rates for pneumococcal disease range from 10 to 30 per cent, substantially higher in the elderly and patients with comorbidities.14 Yet, vaccination coverage rates among adults remain low as immunisation programmes are fragmented and not well implemented across the region. Life-course immunisation can prevent up to 3 million deaths15 from infectious diseases including respiratory viruses annually. It is therefore important that all populations, particularly the older age groups, receive regular vaccinations to prevent future illnesses from arising while reducing the strain of ongoing illnesses.
Data on the incidence of pneumococcal disease is varied across the region, with limited evidence on the humanistic burden of the disease. As the world recovers from COVID-19, countries are looking to recover immunisation services to pre-COVID-19 levels. A key step towards that is to drive awareness of the public health and economic benefits of pneumococcal vaccination in the Asia-Pacific whilst ensuring processes are put in place to enable continuous monitoring of the prevalence of pneumococcal diseases. In the long run, this will improve pneumococcal vaccine coverage and prevent morbidity and mortality, especially in at-risk regions.16
Respiratory Syncytial Virus (RSV)
RSV is the most common cause of paediatric acute lower respiratory tract infection worldwide.17 Globally, RSV leads to substantial morbidity and mortality burden, with one in every 50 deaths in children aged 0-60 months and one in every 28 deaths in children aged 28 days to 6 months.18
In Asia, RSV-related disease burden remains high in tropical countries. In Singapore, RSV causes substantial paediatric health and economic burden as it accounts for 33.5 hospitalisations/1,000 child-years among children < 6 months of age and 13.2 hospitalisations/1,000 child-years in children 6–29 months of age. The annual healthcare cost attributable to RSV is S$6.2 million (US$4.7 million), or S$60 (US$45) per birth.17
A study18 found that RSV passive immunisation programmes that target protection during the first 6 months of life could have a substantial effect on reducing RSV disease burden, but more data is required to understand the implications of the potential age shifts in peak RSV burden to an older age when these are implemented. Currently, treatment options for RSV remain limited and an effective vaccine against RSV is not yet available.19
Moving forward, a two-pronged approach may be necessary to control the spread of RSV in the region. Firstly, the development of effective treatment and vaccines will need to be prioritised, and secondly, regional studies will need to be conducted to better understand the epidemiology of RSV.
Seasonal influenza epidemics cause approximately 3 to 5 million cases20 of severe influenza and about 290,000 to 650,000 respiratory deaths20 each year globally. Although epidemiological data for the Asia-Pacific is limited, the burden of influenza in the region is comparable to that of the temperate regions in Europe and North America. While the influenza A virus is the cause of most influenza illnesses in the region, influenza B has been found to be the dominant strain in some seasons. WHO recommends a range of quadrivalent and trivalent influenza vaccines for use in the 2022 southern21 and northern22 hemisphere influenza seasons, targeted at influenza A and B viruses.
In the Post-COVID World, Routine Immunisation Remains Key In Preventing a Resurgence of Vaccine-Preventable Diseases
Routine immunisation helps to reduce the number of patients that require health services, prevent disease outbreaks, and protect vulnerable populations such as children, the elderly, and patients with existing medical conditions. This will ensure that the entire healthcare system remains sustainable in the long run.
In our efforts to strengthen routine immunisation programmes across the world, we need to recognise the collective action needed to promote the use of vaccines to protect people of all ages against diseases whilst ensuring that all populations, particularly those in low-and middle-income countries, have access to high-quality immunisation programmes.
Moreover, given that the Asia-Pacific is experiencing a growing elderly population at an unprecedented rate and with the number of older persons expected to more than double from 535 million in 2015 to 1.3 billion by 2050,23 there is a stronger impetus to improve the uptake of existing vaccines and increase awareness for life-long vaccination24 to further alleviate economic, healthcare, and societal challenges caused by an ageing society.
At the same time, COVID-19 has shone the spotlight on the value of immunisation and the need for a sustainable approach to build immunisation capacity globally, specifically in areas where populations do not have easy access to vaccines. In the COVID-endemic era, as countries recover essential health services such as immunisation programmes, the private sector and public sector will need to work more closely than ever to accelerate equitable and affordable access to vaccines in lower-income countries.
Cross-sector partnerships will also become more important to accelerate broad, equitable access to vaccines in low- and middle-income countries. The future of immunisation will increasingly be based on integration and collaboration with stakeholders within and beyond health25 as all of us have a part to play in creating a healthier, safer, and more prosperous world for all. [APBN]
About the Author
Dr Aileen Dualan
Head of Global Medical Affairs, Asia Pacific, MSD