A major problem in determining the prevalence of needle phobia is that it usually involves trying to count the number of people who aren't there. A person cannot go into a clinic or doctor's office and ask how many people did not make an appointment that day because of a fear of possible needle procedures. No one will have any idea of what that number would be.
Some studies have been done in medical facilities in an attempt to determine the percentage of needle phobics.  A very significant problem with those studies is that they can count only those needle phobics who were at least brave enough to go for medical treatment. Those suffering from severe needle phobia are necessarily omitted from these studies since there is no way to find and count them. As a result, many of the studies signficantly under-report the prevalence of needle phobia.
All of the studies of needle phobia are problematic because there are so many different degrees and types of needle phobia. Unlike many other disorders, there is no sharp and clear dividing line between who is needle phobic and who is not. Even among those who have the vasovagal (fainting) type of needle phobia, there is no clear dividing line. Estimates of the prevalence of the vasovagal type of needle phobia have ranged from 3.5 percent to 10 percent of the population. Some people with the vasovagal type of needle phobia never completely lose consciousness, but simply often experience episodes of near-fainting. My email indicates that most people who consistently experience a severe vasovagal reaction in association with a needle procedure have simply resolved to never seek medical treatment. Most of those people eventually die at home, leaving others to wonder why they didn't get treatment for what was often an easily-treatable medical condition. (Those deaths are unnecessary because there are ways to overcome needle phobia, but a severe vasovagal reaction is a truly frightening experience.)
Some studies have been done by questioning the general public. It has been hoped that this could help to solve the problem of needle phobics being "selected out" of the studies.
In both 1998 and 2001, a Gallup poll found the percentage of the general population of the United States that claimed to be afraid of needles and getting injections to be 21 percent on both occasions. The Gallup surveys were made during the periods of November 20-22, 1998 and February 19-21, 2001. The percentage was essentially equal (within the margin of error) for men and women.
In October and November of 2006, a study commissioned by Vyteris found that in the United States, 15 million adults and 5 million children over the age of 5 experienced "high discomfort or exhibit needle-phobic behavior when faced with getting a blood draw or injection." According to a Vyteris news release: Of those 15 million needle-phobic adults, approximately 3.5 million indicated they had refused a blood draw or chose not to receive a recommended injection at some point in their life. The numbers were extrapolated from a screening of 11,460 individuals. The overall sampling error was 3.5 percent.
See this WebMD article for more information.
The Vyteris study indicated a percentage of the United States population of less than about 7 percent experienced needle phobia, however the Vyteris survey was looking for people who experienced a much higher level of fear and discomfort than the earlier Gallup poll.
A more recent study on the prevalence of needle phobia was published in 2009 in Australian Family Physician by investigators at the School of Medicine at Griffith University in Logan, Queensland. See:
In that study, 22 percent of patients at visiting a medical general practice facility reported a fear of needles, and 20.5 percent of the patients studied reported a level of fear that had caused them to avoid medical care in certain instances.
In a study at a travel clinic in Haifa, Israel, 21.7 percent of patients indicated a fear of injections and in 8.2 percent of patients, the fear was described as "unreasonably intense." See:
This page is very much a work in progress. I will have more information later.