More reports at the beginning of the vaccination programme, but no suspicion of safety differences between COVID-19 vaccine batches
A new analysis from the Danish Medicines Agency shows that the number of reports of suspected side effects after vaccination with COVID-19 vaccines is highly related to the time the individual vaccine batches were used.
The Danish Medicines Agency has taken stock of the reports of suspected side effects following COVID-19 vaccination submitted to the agency since the Danish vaccination programme was launched at the end of 2020.
The analysis shows that the volume of submitted reports is highly linked to the time when the individual batch was used in the vaccination programme.
“The number of reports of suspected side effects per 100 doses is significantly higher for the batches used early in the vaccination programme. One of the primary reasons for this is that national healthcare professionals were among the first groups to be offered vaccination. This group is by default particularly alert to possible side effects and also has knowledge of the practice for reporting side effects to the authorities,” says Martin Zahle Larsen, Team Leader in Pharmacovigilance at the Danish Medicines Agency.
The elderly and frail individuals were also among those who were offered vaccination early; a group where many have underlying diseases the symptoms and medication of which could be confused with vaccine side effects.
“Lastly, the early phase of the vaccination programme saw a generally high – and natural – vigilance to side effects of COVID-19 vaccination,” explains Martin Zahle Larsen.
This conclusion applies to both mRNA vaccines that have dominated the Danish vaccination programme, i.e. the vaccines from Pfizer/BioNTech and Moderna.
Small batches at the beginning of the vaccination programme
At the beginning of the vaccination programme, the batches used were relatively small compared to the batches that were introduced later in the programme.
“There are several explanations for this. First of all, the production capacity was smaller at the start and then gradually increased significantly. Additionally, the vaccines were distributed between the member states according to joint procurement agreements. This meant that Denmark received relatively small sub-batches in the very early phase of the vaccination programme,” says Martin Zahle Larsen.
Test of vaccine batches in the EU
In the EU, all vaccine batches (like other medicinal products) must be tested by the manufacturer according to analytical methods authorised by the authorities. The manufacturer must demonstrate to the authorities that the test methods applied provide reliable results, and the authorities approve the results/limits considered acceptable for each analysis used. As a result, every COVID-19 vaccine batch was analysed twice, both by the manufacturer and by the authorities. A batch is released for use in the EU if the results of both tests are acceptable.
Read more on our COVID-19 theme page
On the Danish Medicines Agency’s COVID-19 theme page, you can read more – about reports of suspected side effects in general and about the Danish Medicines Agency’s analysis.