I don't know about popular, but they were certainly around. Probably a factor in the ending of use of thimerosal, an ethylmercury based preservative, in vaccines. It was easier to remove that, then to convince some of the anti-vax people that ethylmercury is rapidly eliminated from the body and does not go back in time to give someone autism before they got a vaccine.

That said, the medical community and the internet are not always kind and empathetic. Some kids are really miserable when they get a vaccine and when they do their job and induce an immune reaction, that can be miserable too. If your kid has big reactions, spacing out and prioritizing the vaccines a bit can be helpful. Delayed compliance is better than non-compliance. And there's a lot of people who refuse to accept that there's any risk; it's managable and reasonable, but it's still there and pretending there's no risk plays into the narrative when someone does have a complication.