Indonesia and Thailand are considering booster shots for medical workers immunized with the vaccine made by China's Sinovac.
It comes as concerns grow about Chinese vaccines and their effectiveness against new and more transmissible variants.
In Thailand, a leaked health ministry memo showed a comment warning not to give Pfizer booster shots to medical workers.
The quote was made by an unnamed official, who said that such a move could undermine confidence in the effectiveness of Sinovac.
Thai Public Health Minister Anutin Charnvirakul.
"This is in a meeting which involves various medical professors. They are not civilian staff. Each of them sacrificed their time and were just sharing their views and the minutes of the meeting were recorded. But this doesn't mean the views would turn into action, there are many procedures after that."
Some data has shown Sinovac's vaccine is effective against hospitalization and severe COVID-19 cases.
But there is no detailed data yet on its effectiveness against the highly transmissible Delta variant.
China said this week its vaccines are safe and useful.
That hasn't stopped Singapore from excluding people who received Sinovac shots from its count of total vaccinations due to a lack of data, especially against the Delta variant.
Turkey and the UAE have also started giving booster shots to those inoculated with Chinese vaccines.
The issue is a major challenge for Southeast Asian countries which have relied heavily on China's vaccines due to tight supplies of Western products.