As often as is medically recommended based on your age, where you live, what you do, and where you go. Some vaccines are recommended for babies everywhere, others are boosters of those same vaccines later in life, some or are recommended for specific jobs (such as working in a hospital), and others if you travel to exotic countries. To know which vaccines you or your child should get you should consult a health care professional.
Every year, a horse should be getting a tetanus vaccination.
The current recommendation is to receive a tetanus shot every ten years.
How often should you change the fuel filter?
as often as needed
Lodestone
You should change your oil every 3,000 miles. If you drive your car rough, then you should change it more often.
everyday
The ball band on yarn often tells you what size needles it is suitable for.
How often should you change water pump in a boat
You should change them after every feeding because they should be washed after every feeding.
Every week
you should change it every week so it will always be clean.