As best as we know, transient increases of 10 times or more can occur within days, and usually resolve within 2-4 weeks. This has not been studied closely with daily or weekly measurements to know the exact timing of these bursts. It is unclear whether a transient increase caused by vaccination or illness, results in an increased risk of progression of disease. I doubt very much that a tetanus shot 3 hours before the viral load measurement would affect the results. It will not affect your setpoint.
Vaccinations are an important part of health maintenance.
I support their use, particularly in early HIV when the chances of making effective antibodies are greatest. The first test may be incorrect because of concomitant illness. The second test should be close to where your set point is. If they are wide apart in values, I would get a third test. Experts appearing on this page are independent and are solely responsible for editing and fact-checking their material.