This is maybe not THE good answer, but it could lead to a good one…

Our so popular Influenza_A h1n1 has probably a common genetic signature with all other A_xxxx influenza kind.
As reported by Dr Clark in her book TCFAD, chapter “Pathogen Frequencies”, the Influenza A & B has a Mortal Oscillatory Rate of :
= Low frequency of 313.35kHz
= High frequency of 323.90kHz
= 3mn zapping frequency of 320.315kHz

Most zappers out there are build with a 555 oscillator, designed with a duty cycle of about 50/50.
This excludes most even harmonics, only odds remaining with some energy.
Making some calculations about all this, here is something interesting!

125 = 5x5x5. Only odd numbers. Good for 555, 50%Duty Cycle

313kHz/125 = 2.504kHz very close to 2.5kHz (0.16%)
320kHz /125 = 2.5625kHz. Close to 2.5kHz (2.5%)
323kHz/125 = 2.584kHz. Not so close to 2.5kHz (3.36%)

What a coincidence, if you believe in coincidences!!
Our so popular 2.5kHz seems to be a winner!
This frequency seems to have (if I believe its popularity) enough energy to reach many parasites.
It should be a good one on this (relatively low) 323kHz frequency.

Here is more, playing with numbers :
7 and 9 (3x3) and 11 have too only odd numbers
320kHz/7= 45.71kHz
320kHz/9= 35.55kHz
320kHz/11=29.09kHz
From these numbers, 29.09kHz is close enough to 30kHz to be a good winner, with an optimum transfer of energy for the zapper’s effect, and a quite low harmonic (11th) to have a strong remaining energy at 323kHz.

= If you have a standard zapper with 2.5kHz, it could be close enough to try.
Check your exact frequency. Maybe you are right on the spot.
= If you build your own zapper, use a 15 turn trim-pot to closely adjust your frequency.
You will find here a schematic with values and explanations, using this configuration
http://www.emz.maestro-zapper.com/e_schema_mzap4_tn1.html

= If you have a zapper with adjustable frequencies (M.Zap4R), it will be worth the trouble to re-adjust 30kHz and 2.5kHz to closely match 29.09kHz and 2.5625kHz. Ask your manufacturer to provide information on how to do-it.
= If you have a “function generator” zapper with programmable frequencies, these numbers could be of help.
= If you are a zapper’s manufacturer, these numbers, or other numbers this post could trigger, could be interesting to explore, and maybe to implement.

Good zapping