To answer the question, I followed these steps:

<ul>
  <li><b>Identified the correct indicator</b> for DPT vaccination coverage among children aged 12-23 months.</li>
  <li><b>Found the specific data value for Belgium</b> in 2019 for this indicator, to use as a comparison point.</li>
  <li><b>Listed all countries in the Western Asia region</b> to determine which ones to compare against Belgium.</li>
  <li><b>Retrieved the 2019 DPT vaccination rates</b> for each country in Western Asia.</li>
  <li><b>Counted how many countries had a lower vaccination rate</b> than Belgium by comparing each value to Belgium’s rate.</li>
</ul>

<b>In summary</b>, I compared Belgium’s DPT vaccination rate for 2019 with those of all Western Asian countries and counted the number of countries with a lower rate.

<b>Final answer:</b> 11 countries in Western Asia had a lower share of 12- to 23-month-olds with DPT vaccination than Belgium in 2019.