wherever possible.
Really?
That little caveat says it all.
Perhaps I should have elaborated further.
The document (https://www.immunize.org/talking-about-vaccines/vaticandocument.htm) goes on to state that if an ethically developed vaccine (one free from any use of fetal stem cells in its research and development process) is not available (for either technical or regulatory reasons), one must weigh what is the greater good. If the disease being vaccinated against is a grave threat to the safety and wellbeing of an individual and/or their family, they may decide (within the bounds of Catholic teachings) to take the vaccine, but it then becomes their duty to advocate for the development, production, and regulatory approval of an ethically produced alternative so others may use that instead. Preservation of human life and advancing the availability of an ethical alternative for others together are taken as a greater good.
Now if the vaccine is for athlete’s foot, there is no greater good to be had. One is obligated to avoid it until an ethical alternative is available. If it’s for weaponized smallpox that’s likely going to wipe out your entire family, you should be taking that. In between there is a lot of gray area. That decision is largely considered personal and between you, your conscience, and God. God knows whether you’re making a selfish decision based on preferences or if you’re making the best decision you can based on the evidence before you.
In the US, ethical alternative vaccines exist for everything except rubella and Hep A. There is an ethical rubella vaccine (no fetal stem cells used in its research and development) approved for use in Japan, but it is not approved yet in the US. Measles, mumps, pertussis, influenza, and nearly all others have ethical alternatives available. You just need to ask for them. If your doctor says no, get a new doctor.
More information about the technical side of how and why fetal stem cells are used in the research and development of vaccines is here: https://www.historyofvaccines.org/index.php/content/articles/human-cell-strains-vaccine-development. The long and short of it is that it’s quicker, cheaper, and easier using human stem cells, and fetal stem cells above all. It’s not impossible to use more ethical methods, and if enough people specifically require ethical alternatives, then basic market forces will dictate that ethical methods become the default choice for future R&D.