Danish researchers led by cardiology professor Max Schmeling and Dr. Vibeke Manniche uncovered a startling trend: early batches of Pfizer’s COVID-19 vaccine triggered significantly more side effects than later ones. NTD spoke with Dr. Manniche, who emphasized the need for further analysis to determine if this trend extends to other countries like the United States and if vaccine production or administration changes contributed to the observed differences. However, challenges arise as health authorities appear reluctant to share data, hindering comprehensive research efforts.