Health authorities last week announced the withdrawal of the AstraZeneca vaccine from Denmark’s Covid-19 vaccination programme. That left around 150,000 people who have received AstraZeneca as their first vaccine dose, including a large proportion of healthcare sector workers, in doubt as to when and how they will receive their second dose.
The country’s health authority has since confirmed that people who have received a first dose with AstraZeneca will be offered a second dose from another company
The second vaccine will be offered around 12 weeks after the date of the first one.
“We have reviewed documentation and medical recommendations from other countries and on that basis have concluded that the best offer is to offer everyone who has received one dose of the Covid-19 vaccine from AstraZeneca a second dose with a so-called mRNA vaccine,” Danish Health Authority director Søren Brostrøm said in a statement.
The two vaccines in use in Denmark at the current time, from Pfizer/BioNTech and Moderna, are both of this type.
That is not the case for the AstraZeneca vaccine, which uses a viral vector.
Previous reports have shown experts to have differing views on the use of a different Covid-19 vaccine as a second dose.
Eskild Petersen, a professor in infectious medicine at Aarhus University Department of Clinical Medicine, told news wire Ritzau last week that he would be “relatively comfortable” with the decision.
“I would be relatively comfortable with it. We have no data from the corona vaccines, but we know from other vaccines that it is possible,” Petersen said.
“Studies show that you can boost the old vaccination with the new one. The central thing with vaccines is that they make a protein, in this case a spike protein, which corresponds to the one in the coronavirus. That (protein) is made regardless of whether you take the AstraZeneca or Pfizer vaccine,” he explained.
Another Danish university professor, Camilla Foged of the University of Copenhagen, a specialist in vaccine design, told Ritzau prior to the decision to withdraw AstraZeneca that there was no data to support the effectiveness of mixing vaccines.
“I have not seen data that documents the effect of mixing vaccines,” Foged said.
“When you give the second dose you boost the first (immune) response you have been given. The question is, if you mix vaccines, whether you boost the immune system suffucuently,” she said.
Brostrøm rejected suggestions Denmark was experimenting by mixing vaccines.
“I wouldn’t call it that [an experiment, ed.]. Mixing vaccines has also been seen in other contexts,” he told Ritzau.
“It’s something that has to be done sometimes for various reasons. For example if a member of the public is allergic to the first dose or if you run out of vaccines,” he said.
“So I wouldn’t call it an experiment, but of course it is not something we have huge medical studies on,” he added.
The health director noted that a British study is currently looking at the mixing of Covid-19 vaccines, and that France, Germany and Norway all currently allow doses to be mixed.