The redesign definitely poses some comparability issues with earlier years. It is up to each individual researcher to decide if they think pooling is appropriate for their specific application. That being said, I would encourage you to 1) read the IPUMS (forthcoming) and NCHS (linked in previous post) documentation closely, 2) be cautious when interpreting time trends in 2019, and 3) run analyses without 2019 to see if it drastically changes your results. Given that the redesign only retains the sample adult and sample child aspect, I would also recommend a close examination of estimates that use variables previously available on the household/family/person file that move to the sample adult/sample child records in 2019. While eliminating household/family/person files is the major deviation, I will also note that in earlier years the data include one sample adult/child per family; in the 2019 design it is one sample adult/child per household.
You will be able to pool 2019 data with earlier years via the IPUMS NHIS extract system, so you shouldn’t need to do any additional data management from that perspective. As always, we recommend consulting the weights tab for each variable for information on weighting, as well as relevant documentation as part of our user guide.