“This is a massive beast that we are driving along at enormous pace with enormous success,” he said.
“If you sail a massive liner across the Atlantic then it’s not really reasonable that you aren’t going to have to make at least one course correction during that voyage.”
There have been 79 cases of rare blood clots with low platelets in the UK out of 20 million doses. Nineteen of those 79 people died – three of whom were aged under 30.
The cases occurred in 51 women and 28 men aged from 18 to 79.
“From these reports, the risk of these type of rare blood clot is about four people in a million who received the vaccine,” Raine said. “This is extremely rare.”
Younger people are much less likely to die from COVID-19 so the balance of risks versus benefits from a vaccine was different to older people, Raine said.
The MHRA produced a graphic that examined the rate of intensive care admissions prevented by having the AstraZeneca jab versus the risk of serious side effects from the product. The graphic was on the basis of low community transmission.
For those aged 20 to 29, the rate of ICU admissions prevented from having the vaccine was 0.8 for every 100,000 people. But the risk from serious side effects from the vaccine was 1.1 in 100,000.
The benefits were much higher for older groups.
“With the proven effectiveness against the disease that is still a huge risk to our population, the balance of benefits and known risks of the vaccine is still very favourable for the vast majority of people,” Raine said.
Young people who have already had one dose of the AstraZeneca jab have been told to get their second despite Wednesday’s decision.
Other under 30s will be offered jabs by Pfizer, Moderna or potentially Johnson and Johnson.
Several countries have already imposed limits on who can receive the vaccine, and any restrictions are closely watched since the vaccine, which is cheaper and easier to store than many others, is critical to global immunisation campaigns and is a pillar of the United Nations-backed program known as COVAX that aims to get vaccines to some of the world’s poorest countries.
The European Medicine Agency’s investigation focused on unusual types of blood clots that are occurring along with low blood platelets. One rare clot type appears in multiple blood vessels and the other in veins that drain blood from the brain.
Sabine Straus, the chair of the EMA’s safety committee, said the best data is coming from Germany where there is one report of the rare clots for every 100,000 doses given, although she noted far fewer reports in the UK. Still, that’s less than the clot risk that healthy women face from birth control pills, noted another expert, Peter Arlett.
The agency said most of the cases reported have occurred in women under 60 within two weeks of vaccination but based on the currently available evidence it was not able to identify specific risk factors.
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Bevan Shields is the Europe correspondent for The Sydney Morning Herald and The Age.