Annual check-ups are part of normal prevention, helping your doctor to identify and address potentially worrisome conditions before they become serious. As a patient, you benefit from the health data collected during the visit. You gain insight into whether you need a new medication, or should simply cut back on the cake and cookies.

When looking at global immunization, annual coverage data "check-ups" serve much the same function. They provide insights into the overall health of country immunization systems. They show policy-makers where they’re making headway, and highlight where efforts need to be increased or changed.

At the Bill & Melinda Gates Foundation, we use global immunization data in much the same way your doctor uses your health information: to inform our approach to improving the health of immunization systems and to bring more life-saving vaccines to more kids. To that end, few days of the year are more important than when the World Health Organization (WHO) and UNICEF release their Estimates of National Immunization Coverage - what we in the global health field call WUENIC ("woo-nick"). WUENIC data comprise national estimates of immunization coverage for 194 countries, of which 141 include subnational coverage data for 234,000 districts. This represents two thirds of the global infant population.

If there’s any gold-standard "check-up" for the state of global immunization, it’s this. Year after year, it tells us how well certain countries are doing at protecting their communities against infectious diseases. It gives us a picture of immunization on a global scale. New WUENIC data have just been released, and more kids than ever are being reached by immunization programmes. Here are the "vital signs" that global immunization was in good shape in 2017:

- 122 million children, or 90%, received at least one dose of diphtheria-tetanus-pertussis vaccine (DTP3), and 116 million received all three of the recommended doses.

- 115 million children received the measles vaccine. Global measles mortality has declined by 84% since 2000.

- New and under-used vaccines are increasingly reaching those who need them most. In countries supported by Gavi, the Vaccine Alliance, 1.5 million more children received vaccinations against the leading cause of pneumonia than in 2016, and 3.9 million more children were vaccinated against rotavirus, the leading cause of severe diarrhoea.

- Compared to 2015, 57% more children - an additional 294 million - received the inactivated polio vaccine, which will eventually replace the long-used oral polio vaccine.

The progress in global immunization is testament to the collective efforts of many, from frontline workers in the remote hinterlands to political leaders in state and national capitals, to vaccine manufacturers in advanced facilities around the globe.

This is all positive news. But like any good doctor, I’m wary of complacency leading to backsliding. And the world has every reason not to be complacent when it comes to immunizations. Last year marked the first time that WHO and UNICEF included disaggregated, subnational data. This shift to a greater use of data to unpack strengths and weaknesses at a more granular level is essential to our work. So, while the topline national estimates look good, our "checkup" is not complete until we examine the subnational data too.

Here, we see that progress is more uneven. Last year, nearly 20 million infants worldwide did not receive all their basic childhood vaccines. Half of them live in just five countries: Ethiopia, India, Indonesia, Nigeria and Pakistan. Tragically, one in ten kids globally have not received vaccines of any kind, leaving them vulnerable to deadly and disabling - yet entirely preventable - diseases, such as diphtheria, measles, polio, pneumonia and rotavirus.

While childhood immunizations have increased worldwide, children in fragile states - countries characterized by weak state capacity, violent conflict or poverty - are being left behind, recent analysis by Gavi, the Vaccine Alliance shows. DTP3 coverage stagnated at or around 62% in fragile states from 2010 to 2017, while the figure rose from 80% to 86% in non-fragile states.

But the total number of kids is just part of the story. We’re interested in equity too, and major subnational discrepancies in immunization coverage remain. Only a quarter of countries meet the goal of having at least 80% coverage in every district and 90% coverage nationally. We know that an additional 1.5 million deaths can be avoided every year if immunizations can be delivered to every child, everywhere. This reality makes for a challenge that vaccine advocates cannot shy away from. It’s one that never rests, no matter the progress we see on a global level.

In the coming months, country governments and those of us working in global health will continue to parse this year’s data to make sense of its lessons. It helps us strategize about how we can help countries do better, achieving more progress in some of the hardest contexts in the world. Because, just like going in for an annual check-up, getting the data is only half the battle. Doing the hard work comes next.