Delaying could have two meanings so you have to figure out which one it is from the context. 1 it could be the noun form of the verb so the meaning would be similar to 'if you want to delay a vaccine then...' 2 it could be the adjective form of the verb with s meaning similar to 'if you like vaccines that cause a delay then...'

I think this quote is from "Hype: a Doctor's Guide to Medical Myths" by Doctor Nina Shapiro. It's been over a year since I read it, but I think this chapter was about the dangers of seeking medical advice online.

Chantae is correct about the literal meaning of the phrase, but may be incorrect about the context. Delaying means to make something late or take longer. Vaccines are a preventative measure against illnesses. Vaccines work by introducing a small amount of an illness into a person to create cells that know how to fight the illness. The most common vaccine is the flu vaccine that is typically given every year in the United States. If you are asking about the phrase in relation to Covid-19 it would mean taking more time to create a medicine that could prevent Covid-19.

In the US, children normally get a standard series of vaccinations every year until they are six years old. This way, then enter school with full immunization. Recently, many parents have been choosing not to vaccinate their children at the usual times. So I believe that the writer is talking about parents who want to wait until their children are older to get vaccinated.