As an addition (and correction) to this, powerful thermonuclear weapons don't vaporize anyone either. They are targeted for high-altitude airbursts and kill through a combination of burns and building collapse, plus secondary fires, infection and breakdown of emergency services. The majority of the victims would not die an instant death.
There are multiple lethal effects from nuclear weapons, and a person inside the 100 million Celsius fireball itself (TK-radius), yes, will be vapourised.
Fireball size depends on weapon yield. For a 1 MT weapon, the radius is roughly 870m, at 5 MT ~1010m, at 150 KT, about 250m.
Most US nuclear weapons yield between 600 to 2,200 KT (0.6 to 2.2 MT).
Whether or not individuals are within the fireball radius depends on the height of detonation, parameters of the nuclear explosion itself (shaped nuclear charges are theoretically possible, though I'm not aware whether any present weapons are designed as such), and of course the local population density.
Outside the fireball, the principle lethal mechanism is the shock wave, though thermal pulse can still provide severe burns, and initial and fallout radiation can also be lethal, though over longer periods (hours, days, weeks, or more).
Effects generally fall with the inverse cube law. Larger weapons also experience an inverse cube effect, such that a one thousandfold increase in weapon yield delivers only a tenfold increase in effects at a given distance.
People may be vapourised, though most within a blast effect area will likely not. They may however be severely burned if directly exposed to the thermal pulse. Near in, other lethal effects, which may be delayed by a few seconds, principally from the blast wave, should predominate.
Air-burst attacks would likely decrease vapourisation. Penetrating / shaped charges would have markedly different and highly directional effects.
Blast effect falls off approximately as distance cubed, because the overpressure wave deposits energy in the volume and disperses gradually. Thermal radiation, on the other hand, falls of as distance squared, more or less. This is why the main damage mechanism goes from radiation to blast to thermal as the bomb gets larger.
For more information: https://nuclearweaponarchive.org/Nwfaq/Nfaq5.html