Hello,
Thanks for posting your query.
During a cold it's recommended to eat hot , soft , easily digestible home made food as much as feasible as this helps in better absorption of nutrients and plenty of fluids to prevent dehydration.However an occasional pizza ( avoiding extra spices) would not do any harm if adequately chewed and taken with good amount of fluids .
During a bout of Dengue ( viral hemorrhagic fever) its best to avoid it because the condition involves decrease in the body's platelet count ( cells which help in blood clotting). Thus there is a great risk of internal bleeding either from gastrointestinal tract or anywhere else in case of Dengue .
So as far as possible hard difficult to digest and spicy or processed foodstuffs are to be avoided and very importantly plenty of water and other fluids ( more than the usual intake ) is advisable .
Hope I have answered your query.
Kindly accept my answer in case you have no further queries.
Regards

---