Dear Phung, thank you very much for taking the time for this interview.

Could you briefly tell us about your background and your current research focus?

I received a BA in biological chemistry and a Master of Public Health in the USA. In 2007 I completed my PhD in Epidemiology from the University of Basel. My research focuses mainly on vaccination coverage, the epidemiology of vaccination and its impact on infectious diseases and factors affecting vaccination uptake in the population.

You are involved in a national survey focusing on the vaccination status of children and adolescents in Switzerland.
Could you give us a brief overview of the survey and explain its goal?

The Swiss National Vaccination Coverage Survey (SNVCS) assesses vaccination coverage of recommended childhood vaccine preventable diseases of children ages 2, 8 and 16 years in all 26 cantons every 3 years. It is a collaboration between the cantons, the Federal Office of Public Health (FOPH) and EBPI since 1999. The results are used to evaluate compliance with the vaccination recommendations in the Swiss National Vaccination Plan, measuring the progress of the Swiss Vaccination Strategy, assessing the protection level in the population and planning future vaccination interventions and campaigns. Vaccination coverage data are publicly available to all on the FOPH website: https://www.bag.admin.ch/bag/de/home/gesund-leben/gesundheitsfoerderung-und-praevention/impfungen-prophylaxe/informationen-fachleute-gesundheitspersonal/durchimpfung.html

How is the survey conducted and which data collection methods are used?

The SNVCS is a survey that randomly selects children in the targeted age groups to participate in the study. The families are requested to submit a copy of their child’s vaccination data. They are contacted 3 times per mail and telephone. This method is conducted in all 26 cantons for all 3 age groups over a 3-year period. In cantons Vaud, Basel-Stadt and Jura, data for the schoolchildren are collected by the schools and shared with EBPI for analysis.

What were the most important findings or trends that emerged? Did any of them surprise you?

Since the establishment of the SNVCS in 1999, we saw considerable changes in vaccination uptake throughout the years for all 3 age groups. Of particular importance is measles vaccination uptake at 2 doses, where the 95% threshold to achieve herd immunity has been reached by the schoolchildren and is only 1 percentage point away for the 2-year-olds. Measles vaccination coverage increased 23 percentage points for the 2-year-olds, 57 for the 8-year-olds and 42 for the 16-year-olds, between 1999-2022, thus contributing to the measles endemic free status in Switzerland. Furthermore, we see a constant uptake of all basic, complementary and supplementary vaccinations recommended in the vaccination plan, reflecting the acceptance and success of the Swiss immunization program. However, efforts are needed to maintain this high level, but also to increase uptake where needed, for continued protection against vaccine preventable diseases.

Did you encounter any challenges or obstacles during the survey?

Throughout the years working on the SNVCS, the biggest challenge has been the declining participation level from ca. 85% in 2005 to ca 60% in 2022. This decline is due to many different reasons, such as fear of Big Data and the concern for data security and data protection, resulting in less people sharing data. The very polarised discussions about vaccinations during the pandemic have also led to many people being less interested in providing information on this topic as vaccination has become increasingly a topic to be discussed privately in the family. In addition, we simply had no contact with most of the non-participants and they did not respond to our requests, indicating a lack of interest among the population in participating in a survey. Furthermore, many households were also overwhelmed by the constant attempts from telemarketers to solicit interests and participation in their products, creating negative attitudes towards unrecognized telephone numbers and contacts for participation in the SNVCS. Finally, the participation level is also hindered by those who are vaccine critics, as they tend to participate less in the SNVCS. Although vaccine coverage is routinely assessed for children, this information is lacking for adults as no such system is available. In some countries, vaccination data are automatically entered in an immunization registry. From this registry, vaccination coverage could easily be calculated for the entire population, saving much time and effort while avoiding biases and limitations. The establishment of a comprehensive registry demands collaborative efforts, necessitating policy adjustments and organizational restructuring at both national and cantonal levels. Simultaneously, fostering acceptance at the individual level is imperative. Despite these challenges, undertaking this initiative represents a substantial and worthwhile investment in public health, one method to ensuring the protection of the population..

Can you say something about how Switzerland compares internationally in this regard?

Compared to the estimates reported globally and for the World Health Organisation (WHO) European region, vaccination coverage of 2-year-olds in Switzerland for recommended childhood vaccine preventable diseases is higher, except for those for Hepatitis B. Switzerland is also one of the few countries worldwide that has established a surveillance system that routinely monitors vaccination coverage of children.

Your survey looked at vaccination data for the years 2020-2022. What impact, if any, did the COVID-19 pandemic have?

Based on the data that is available and for the period 2020-2022, a preliminary analysis recently conducted by my group revealed that the COVID-19 pandemic has no effect (positive nor negative) on vaccination coverage for the 2-year-olds in Switzerland. Further analyses are recommended to include data from survey collection year 2023, where children born during the pandemic will also be integrated into the evaluation. This will provide a more comprehensive overview of the impact of the pandemic on vaccination uptake.

Do you think the pandemic may have affected population attitudes toward vaccination in general? Was there any indication of this in the survey?

While we did not see a discernible effect of the pandemic on vaccination coverage of the 2-year-olds in Switzerland (as mentioned above), I do think that the pandemic had a broader impact on the perception of vaccination both nationally and globally. As our survey instrument (SNVCS) does not specifically assess vaccination perception, our dataset does not enable a direct measurement of the aforementioned influence. Nevertheless, anecdotal evidence, supported by findings from complementary studies, suggests a notable shift in public awareness and knowledge regarding vaccination (along with the whereabouts of the vaccination certificate) during the pandemic. Notably, discussions on vaccination became more prevalent as a crucial measure to control the spread of the disease. The pandemic prompted an increased scrutiny of topics, such as safety and efficacy of the Covid-19 vaccines, given their expedited development and approval. Furthermore, issues of vaccine equity and access underscored global disparities between rich and poor countries. Heated debates were ignited by vaccination mandates and policies while the altered risk perception of infectious diseases was influenced by the diverse public health measures implemented during the pandemic. These discussions, coupled with misinformation and conspiracy theories, may have contributed to a rise in vaccine hesitancy. In Switzerland, the absence of a decline in vaccination coverage for routinely recommended vaccinations (ex: measles, diphtheria) among children, suggests that the pandemic’s impact is more closely associated with a critical assessment of the public health authorities and their recommendations, particularly regarding non-routine vaccinations, such as those developed using mRNA technology for Covid-19. This nuanced perspective underscores the need for continued research and public health communication strategies to address evolving perceptions in the wake of global health crises.

According to the WHO Europe assessment, endemic measles transmission in Switzerland has been considered "interrupted" since 2016. Furthermore, Switzerland achieved "measles eliminated" status in 2018. What do you think contributed to this success?

There are many factors that contributed to the elimination of endemic measles in Switzerland. The Measles Elimination Program 2011-2020, recommended by the World Health Organisation and implemented in Switzerland played a deciding role in this success. This Program involved a comprehensive strategy that included various components focusing on achieving high measles vaccination coverage and strengthening healthcare systems. These components are: achieving high vaccination coverage, having a strong immunization program, conducting supplementary immunization campaigns, establishing and maintaining robust surveillance systems to detect measles cases and outbreaks promptly, strengthening healthcare systems, raising awareness about the importance of vaccination, addressing vaccine hesitancy and misinformation, and involving diverse stakeholders from health care providers to insurance companies to the FOPH. It is important to note that achieving and maintaining measles elimination status requires ongoing efforts. There is always risk of imported cases, making it important to sustain high vaccination coverage, strong surveillance systems and a regular review of vaccination policies and epidemiological situations. For example, the recent pandemic caused a resurgence in global measles cases as it significantly impacted immunization systems performance. Alone in the WHO European Region, 30’000 cases have been reported between January and October 2023 compared to 941 in 2022.

Nevertheless, isolated measles cases continue to crop up sporadically. Why do you think smallpox could be defeated with the vaccine, but not measles?

Elimination of a disease depends on many factors, which include the characteristics of the disease, availability and effectiveness of the vaccine, transmission dynamics and global eradication efforts. While there are effective vaccines against both diseases, the vaccines themselves were different. The vaccine for smallpox was heat stable and required only one dose, which could be administered from birth and onwards. In contrast, the measles vaccine is less stable, depending on cold chain requirements for storing and transporting; it also required two doses which are recommended 6+ months, presenting logistical hurdles to maintain the vaccine’s potency. Furthermore, the basic reproduction number (R0) for smallpox is small, indicating that each infected person typically only transmits the virus to few individuals; in contrast, the R0 for measles is high, meaning a larger proportion of the population needs to be immune to prevent sustained transmission, with the necessary threshold to achieve herd immunity at 95%. Attaining and sustaining high levels of measles vaccination coverage is challenging, particularly in regions marked with pockets of insufficient immunization. The presence of fragmented health systems and weak healthcare infrastructures, coupled with vaccine hesitancy and misinformation contributes to suboptimal vaccination rates and leaves communities vulnerable. Unlike the era when efforts were made to eradicate smallpox, there is currently much more global travel and migration, creating hurdles in containment efforts and increasing the risk of measles spreading to different regions. Unforeseen events such as pandemics and conflicts, further complicate the global endeavor to eradicate measles. Continued commitment, as well as ongoing dedication to overcome existing challenges and adapt strategies to evolving dynamics, is necessary to sustain the substantial progress that has been made in reducing measles incidence and moving towards measles elimination and eradication.

Are you involved in any other research projects here at EBPI? Are there any other ongoing or upcoming research projects that you would like to draw attention to?

Upon joining EBPI 20+ years ago, my primary focus was on establishing the SNVCS and the cultivation of collaborative partnerships with all 26 cantons and the FOPH. With the successful implementation and seamless operations of the methodology, my scope of research has expanded significantly. Utilizing the expansive and comprehensive SNVCS database, our research endeavors have delved into various facets of vaccination, including compliance, vaccine effectiveness and factors influencing acceptance. Recently, we secured funding from the Swiss National Science Foundation to employ machine learning techniques for predicting vaccine hesitancy based on SNVCS data. Over the last six years, our research efforts have extended to conducting surveys that assess vaccination coverage among adults and health care providers, filling a critical information gap within Switzerland. Currently, we are conducting a clinical study to investigate the immunity of adults aged 18-49 who have received two doses of against measles, mumps and rubella vaccinations, as well as to examine the trajectory of immunity after booster vaccinations. In addition to our ongoing research on vaccination uptake, we also plan to develop intervention projects using insights derived from our research findings and other pertinent published data. This includes developing targeted vaccination campaigns, for example those aimed at enhancing tick-borne vaccination uptake within the population. Our commitment to advancing knowledge in the field of vaccination is underscored by both our research initiatives and the practical applications that stem from our findings.

Thank you very much for this interesting interview!

Interview: Sofia Ricar