The German cities of Berlin and Munich on Tuesday suspended vaccinations with the AstraZeneca jab for under-60s, as further reports emerge of blood clots among people who have received it.
"We are provisionally stopping vaccinations with AstraZeneca for under-60s," said Berlin's health minister Dilek Kalayci, citing "new data about side effects".
She said it was a "precautionary measure" pending an official recommendation from federal health authorities.
The southern city of Munich announced its own suspension shortly afterwards and reports suggested the Brandenburg region had followed suit.
Frequently Asked Questions
A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.
There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.
Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.
Germany's regional and federal health ministers will meet at short notice on Tuesday evening with the vaccine commission expected to make a new recommendation soon.
"We have no serious cases of side effects in Berlin," said Kalayci, adding that "everyone who has already received a first jab of AstraZeneca has very good protection".
Germany's medicines regulator Paul Ehrlich Institute (PEI) has now reported 31 cases of blood clots in people who have received AstraZeneca, Spiegel magazine reported on Tuesday.
Almost all cases are reportedly in younger and middle-aged women, prompting several German hospitals to suspend the use of the jab for women under 55 this week.
A clinic in North-Rhine Westphalia, Germany's most populous state, said it was halting AstraZeneca jabs to investigate two reported cases of thrombosis, while Berlin's Charité hospital extended its suspension to all under-60s following Kalayci's announcement.
On Monday, Canada also recommended halting the use of the jab for under-55s "pending further analysis".
The AstraZeneca vaccine has had a rollercoaster ride, with Britain, which developed it, staunchly supporting its use, South Africa outright rejecting it, and more than a dozen EU nations suspending shots in mid-March before most restarted rollouts but with a patchwork of age restrictions.
France has limited its use to over-55s, while Spain to under-65s.Germany's vaccination campaign has been sluggish, with official figures showing around 11 percent of the population have received a first dose so far.