Health authorities in France and Germany are advising that people under 55 who have received a first dose of the AstraZeneca Covid-19 vaccine should receive a second dose of a different vaccine.
Worries about a link between the AstraZeneca vaccine and unusual blood clotting has led the governments there and elsewhere to restrict that vaccine to older people.
That has raised the question of which second shot should be given to younger people who have already received one AstraZeneca dose.
Germany decided last week that the AstraZeneca vaccine would be given only to people older than 60, after medical authorities said that the blood clotting side-effects mostly affected younger recipients.
Younger people in Germany who had already received the shot, mainly healthcare staff and other critical workers, are now advised by the country’s vaccination authority to take the second shot from another vaccine.
French health authorities have recommended that people under 55 who have taken one dose of the AstraZeneca vaccine use the one developed by Pfizer and BioNTech or another company as their second dose.
The decision affects a half-million people, mainly healthcare workers, French officials said.
Health Minister Olivier Veran described the move as a precautionary measure. “It’s totally logical,” he said.
Italy and Spain have both said they would recommend the AstraZeneca shot only for those over 60, and Belgium for those over 55. Italy recommends getting a second dose of the AstraZeneca vaccine while Spain and Belgium haven’t made decisions yet. The U.K., which has advised using another vaccine for those 30 and under hasn’t recommended giving a different shot to those already vaccinated.
Different Covid-19 vaccines haven’t been systematically combined so far but several studies are under way using volunteers.
Immunologists said the mix-and-match strategy is a tried-and-tested method of enhancing the body’s immune response to beat back invaders. The approach, known as heterologous prime-boost vaccination, has been turned against other infectious diseases, including Ebola, malaria and tuberculosis, and has been used to sharpen the body’s assault against pathogens that cause some cancers and against the tumors themselves.
By combining shots that can train the immune system to recognize and attack a pathogen in subtly different ways, the body might assemble a bigger or better-equipped army to beat back any invaders it encounters, according to researchers.
The combination strategy might avoid the risk with a traditional two-shot vaccine that the immune system repels the vaccine the second time around.
Russia’s Sputnik V vaccine follows the mix-and-match idea by using a different viral carrier to train the immune system against Covid-19 in each of its two doses.
The possible association between blood clotting and vaccinations hasn’t been made with other manufacturers’ Covid-19 vaccines.
Meanwhile, the AstraZeneca shot hasn’t been authorized for use in the U.S.
