Is there any scientific reason that is valid to avoid vaccinations?

Absolutely none: The "science" that linked vaccination with autism was found to be fraudulent and was retracted by journal that published it. One of the main reasons why childhood mortality is so much lower than it was in centuries past is the availability of vaccination. How tragic that we're now seeing children die due to vaccine-preventable diseases.

Scientific?: The bottom line is a risk-benefit analysis. Potentially fatal infections such as tetanus, polio, whooping cough and measles versus mostly minimal side effects. Would one walk across a busy interstate with a blindfold on? Would you choose to ear raw chicken without cooking it? Would you drive drunk? Rational people get vaccines and allow their children to be immunized.