The ongoing coronavirus disease-19 (COVID-19) pandemic, caused by a novel coronavirus, namely, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has disrupted global health services and vaccination activities. The current pandemic has caused a drop in routine immunization (RI) coverage, as well as delayed supplementary immunization activities (SIAs) in many low- and middle-income countries (LMICs).
Study: COVID-19 impact on routine immunisations for vaccine-preventable diseases: Projecting the effect of different routes to recovery. Image Credit: alinabuphoto/Shutterstock
In March 2020, the World Health Organization (WHO) recommended a temporary suspension of mass vaccination campaigns and continuation of RIs, while maintaining COVID-19 prevention measures. In the latest national pulse survey, conducted by WHO, on the continuity of essential healthcare services during the COVID-19 pandemic revealed a reduction in vaccination disruption in many countries. This report documented a decline in the number of countries that faced disruptions to immunization services, from 62% of 129 in 2020 to 37% of 112 countries in 2021.
Institute for Health Metrics and Evaluation (IHME) estimated the disruption of vaccination services until July 2020, based on various data sources such as survey data, reports from electronic immunization systems, data on human mobility patterns and, monthly administrative data on health services.
IHME projected a decline of 7-17% in coverage of third diphtheria-tetanus-pertussis (DTP3) dose in 2020. Additionally, IHME also predicted a decline in the first dose of the measles-containing vaccine (M CV1) by 7.9% in 2020. However, researchers emphasized that levels of disruption in immunization vary significantly from one region to another.
Many countries and international organizations have worked hard to bring vaccination programs back on track, and according to a report, more children had been vaccinated in December 2021 compared to December 2020. Between 2000 and 2020, Gavi (the vaccine alliance) has supported the immunization of over 888 million children through routine programs.
These efforts have prevented more than 15 million future deaths. Mathematical models help scientists evaluate the impact of vaccination by projecting the number of infections, deaths, and other related issues that were averted owing to a specific vaccine.
The Vaccine Impact Modelling Consortium (VIMC) consists of many independent modeling groups that can estimate the vaccination coverage without COVID-19-related disruptions across LMICs and project the number of deaths averted owing to vaccinations. A previous study revealed that delays in measles, Neisseria meningitidis serogroup A (MenA), and yellow fever (YF) vaccination had increased the risks of disease outbreaks. Scientists have highlighted the importance of estimating the long-term impact of different routes to recovery to determine their effectiveness.
A new study
A new study published on the medRxiv* preprint server has focussed on determining the impact of COVID-19 associated interferences with different recovery scenarios for ten vaccine-preventable diseases (VPDs), namely, hepatitis B (HepB), Haemophilus influenzae type b (Hib), human papillomavirus (HPV), Japanese encephalitis (JE), measles, rotavirus (Rota), rubella, Streptococcus pneumoniae (PCV), MenA, and YF, to understand the level of RI changes and its impact during the current pandemic.
The authors utilized the impact extrapolation (IE) method, developed by the VIMC, to measure the changes of RI coverage post COVID-19 pandemic. They focussed on deaths averted due to RIs occurring between 2020 and 2030 and studied two recovery scenarios relative to a non-COVID-19 situation. Researchers observed a 10% drop in coverage in 2020, and subsequently linearly projected if the immunization agenda (IA2030) could be reached by 2030 or fall short by 10%.
Scientists reported a decrease in RI coverage that resulted in fewer fully vaccinated persons (FVPs) and higher mortality. This study revealed that when IA2030 targets fall short by 10%, it causes 11.26% fewer FVPs and 11.34% more deaths between 2020 and 2030, relative to the no-COVID-19 scenario. They projected that on reaching the IA2030 targets, the estimated numbers would be reduced, i.e., 5% fewer FVPs and 5.22% more deaths. The effect of the disruption of RI due to the COVID-19 situation varies across different VPDs. For instance, HPV has been estimated to have a relatively lower impact compared to the other VPDs. Other VPDs such as JE and MenA have been projected to experience a higher impact, particularly if the IA2030 targets are not reached.
IE methodology is time efficient and enabled scientists to focus on proportional changes in FVPs and deaths for each of the VPDs analyzed. Although this method can accurately estimate small changes to RI coverage, it becomes less accurate when the changes are larger or when SIA gets delayed or canceled. Additionally, in the case of some outbreak-prone VPDs, such as measles, MenA, Rota, Rubella, and YF, the IE method tends to overestimate the impact of COVID-19-related vaccination disruptions. This occurs, especially in areas with existing immunity from earlier vaccination activities.
Scientists will aim to accurately evaluate larger changes that include both RIs and SIAs in the future. They have also planned to design new models to capture herd immunity effects and possible outbreaks. The authors emphasized that enhancement in vaccination coverages and addressing immunity gaps will play an important role in reducing the mortality rate over the coming years.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.