Phung, it's been almost two years since we last spoke. What have you been up to during this time?

Over the past two years, my work has continued to evolve around the Swiss National Vaccination Coverage Survey (SNVCS), which remains a cornerstone of vaccine surveillance in Switzerland. With the system now well established and operating smoothly, I’ve been able to expand into several new research areas and projects.

That sounds exciting! Please tell me more.

We have finished the recruitment for our clinical study on MMR immunity in adults aged 18-49, which investigates immune persistence and the effects of booster vaccination. Importantly, my team has expanded its focus to include HPV vaccination and elimination efforts. We recently completed a nationwide HPV study assessing vaccination acceptance and compliance among adults aged 18-45. We found that 27% of the population were vaccinated against HPV, with females better vaccinated than males and younger adults 18-26 better than adults 27-45.

I am also part of a group working on developing a strategy and road map to eliminate HPV-associated diseases in Switzerland by 2030, which is in line with the WHO’s elimination goal. We are using our surveillance infrastructure to better understand HPV vaccine uptake, identify barriers, and design interventions to move Switzerland closer to this important public health milestone.

Have there been any notable changes or updates in the SNVCS project?

We recently completed a Swiss National Science Foundation-funded project to apply machine learning methods to predict vaccine hesitancy using SNVCS data. By combining epidemiological research with data science, we were able to identify key risk patterns. Our results confirmed that vaccination history, as well as regional and socioeconomic variables, such as GDP, pediatrician density and political orientations, were significant determinants of vaccine hesitancy.

Another important development has been the digital transformation of vaccination surveillance in Switzerland. We recently received a seed grant to develop a pipeline for digitizing vaccination cards, transforming them into an interoperable database that can be integrated into the national digital health systems. This infrastructure will allow more efficient, near real-time monitoring of coverage, improve data linkage, and reduce administrative burden. Establishing a fully digital national immunization registry remains a long-term goal, but one that would significantly strengthen public health surveillance and capacity.

What's your take on the current international landscape of childhood vaccination coverage?

Globally, vaccination coverage is under pressure. While some countries have maintained strong systems, many have seen stagnation or decline, especially following the COVID-19 pandemic. These gaps are visible not only in routine childhood immunizations such as MMR, but also in newer vaccines like HPV.
In Switzerland, we’ve been fortunate to see stability in vaccination coverage among 2-year-olds, with no major drop during the pandemic, which is a testament to strong infrastructure and trust in healthcare providers. However, similar to many high-income countries, we do see gaps in adolescent vaccination, especially HPV, where coverage remains below WHO elimination thresholds.
The pandemic has also reshaped public perception: it increased awareness of vaccination certificates and the role of immunization in controlling disease, but also fueled skepticism around safety, equity, and mandates. These shifts are now influencing attitudes not only toward COVID-19 vaccines but also routine and preventive vaccines.

Even a well-resourced country like the U.S. is struggling with a declining vaccination rate for MMR, which is slipping below herd immunity thresholds. What factors do you believe are driving such backsliding in well-resourced settings?

The decline in vaccination coverage in well-resourced settings is multifactorial. Attitudinal barriers such as misinformation and distrust, amplified through social media, tend to predominate in such settings. But structural and administrative barriers also persist: fragmented healthcare systems, difficulties in access, and limited coordination between providers can all contribute to missed vaccinations.

How can these issues be tackled?

Addressing both dimensions is essential. On the attitudinal side, we need sustained, transparent communication and stronger engagement with trusted healthcare professionals.

Structurally, we can learn from Switzerland’s approach: strong coordination across cantons and national levels, accessible vaccination services, and robust data collection. The ongoing digital transformation of vaccination systems will be key here, such as digital vaccination registries, vaccination cross-checks and automated follow-up could reduce missed opportunities and improve public trust through transparency and accountability. Findings from research and other international studies show that reducing structural barriers, can significantly enhance vaccination uptake, even among hesitant populations.

What else could other countries like the U.S. learn from Switzerland's approach?

Switzerland’s experience provides several valuable lessons. The SNVCS, established in collaboration with all 26 cantons and the Federal Office of Public Health (FOPH), offers a model for reliable, representative surveillance that could be adapted to other countries to reduce bias and improve monitoring.

Additionally, our HPV and TBE vaccination research and ongoing digital health initiatives may provide insights for other nations. In collaboration with the FOPH, we conducted a retrospective case-control study using case data from the national mandatory disease reporting system to estimate TBE vaccine effectiveness. We found that overall vaccine effectiveness was approximately 95%, with protection remaining high even 10 years after the completed primary vaccination. These findings were essential in supporting the use of the 10-year booster intervals currently in place in Switzerland, which has since become a model for TBE vaccination recommendations in other European countries. Based on this research, TBE vaccination recommendations in Switzerland were amended in 2024, lowering the recommended age for the first vaccination from six to three years and extending the vaccination to 25 of the 26 cantons.

Furthermore, as Switzerland continues to advance its digital transformation in healthcare, our current digitization initiative provides a practical example for other countries facing similar challenges. Linking electronic health records with vaccination data offers considerable potential to identify populations with low vaccine uptake and design targeted interventions. Such digital integration could substantially improve both childhood and adolescent vaccination coverage not only in Switzerland but globally.

Switzerland's vaccination coverage is quite high, yet there aren't any mandatory vaccinations. Why is that?

In some countries, like Italy, vaccinations are mandatory and accepted. In Switzerland, however, mandatory vaccination would not be possible due to the country’s political and cultural framework. Nevertheless, Switzerland’s success demonstrates that mandates are not necessary to achieve high vaccination coverage. This success lies in the strong trust between the public and healthcare providers, coupled with high-quality, transparent data and effective collaboration between federal and cantonal authorities, as well as health insurers.

In your opinion: To what extend is vaccinating a private decision?

While vaccination in Switzerland is legally a private decision, its consequences extend well beyond the individual. Choosing not to vaccinate affects community protection, especially for those who cannot be vaccinated, such as infants or immunocompromised individuals. In this sense, vaccination is both a personal choice and a public responsibility—an individual decision with collective implications for public health. Published data have shown that when parents and healthcare providers clearly understand this collective dimension, acceptance increases.

Please elaborate the importance of childhood vaccinations and herd immunity for a country.

Childhood vaccination remains one of the most effective public health measures. For diseases like measles, achieving 95% coverage is essential to prevent outbreaks and protect the population. The same principle applies to HPV elimination: to reach WHO targets, we need at least 90% HPV vaccination coverage in girls by age 15. These thresholds are difficult but achievable through sustained effort and trust.

How safe are current recommended childhood vaccinations?

Modern vaccines, including HPV, TBE and MMR, have excellent safety profiles. They undergo rigorous pre-licensure trials and continuous post-marketing surveillance. Adverse effects are exceedingly rare, especially compared with the severe complications of the diseases they prevent — such as encephalitis and pneumonia in measles, or cervical cancer in HPV. Switzerland’s continuous monitoring through pharmacovigilance systems contributes to maintaining this trust.