There are currently no guidelines on the “mixing and matching” of COVID-19 vaccines, the European Medicines Agency (EMA) clarified on Wednesday (7 April), as several European countries are now considering mixed vaccination strategies.
“The EMA hasn’t issued guidelines relating to the mixing and matching different vaccines between the first and second dose,” Peter Arlett, head of data analytics and methods task force, told a press conference on Wednesday.
He noted there is currently a lot of discussion about this option, which he said is driven mainly by the need to optimise the “relatively limited availability” of the different vaccines that have been authorised.
He added there is “theoretical reason to think that mixing vaccines could work, and could be a safe and effective approach,” but confirmed that no data has been submitted to the EMA and therefore no assessment has been made for mixing COVID-19 vaccines.
“If such data becomes available, we’ll immediately assess it,” Arlett said.
The comments come on the back of fresh concerns over the safety of the Vaxzevria, the COVID-19 vaccine produced by pharmaceutical company AstraZeneca, after a number of reports suggested a possible link between the vaccine and rare blood clot incidents.
This has led prompted a number of countries to suspend the rollout of AstraZeneca vaccines in recent weeks. While many countries subsequently resumed the vaccine rollout, some have opted to impose age restrictions.
This now leaves a number of people who have received the first dose of AstraZeneca but are no longer eligible for the second in the lurch.
The UK announced on Wednesday that it would restrict the use of the AstraZeneca vaccine in under-30s over fears linked to blood clots.
Meanwhile, Germany recommended on 1 April that those under 60 who have had a first AstraZeneca shot should receive a different vaccine for their second dose.
While some experts suggest that different vaccine combinations could work together to enforce the body’s immune response to the virus, there is currently no evidence it will be as effective.
This decision raised eyebrows, as there was no scientific data at the time demonstrating that mixing two coronavirus vaccines was safe and effective. Research into this is currently ongoing.
Despite assurances from the EMA just a few weeks ago that the benefits of the AstraZeneca vaccine continued to outweigh the risks, concerns were renewed this week after a senior EMA official said in an interview published on Tuesday that there was a link between the vaccine and rare blood clots in the brain.
After convening several emergency meetings on the matter, the EMA’s safety committee, PRAC, concluded on Wednesday that unusual blood clots with low blood platelets should be listed as very rare side effects of Vaxzevria.
“EMA is reminding healthcare professionals and people receiving the vaccine to remain aware of the possibility of very rare cases of blood clots combined with low levels of blood platelets occurring within 2 weeks of vaccination,” they warned.
So far, most of the cases reported have occurred in women under 60 years of age within two weeks of vaccination.
However, based on the currently available evidence, specific risk factors have not yet been confirmed. This means that, for the moment, the EMA’s guidance on the vaccine remains unchanged.
“Indeed it seems the risk is predominantly in younger age and predominately affects women,” said PRAC chair Sabine Straus, but also pointed to the fact that more women have also been vaccinated in the EU.
Highlighting that COVID-19 is a very serious disease, Straus stressed that the benefits of the AstraZeneca vaccine have been well established and that it prevents disease, hospitalisation and mortality.
“PRAC feels that the overall benefits outweigh the risks,” she concluded.
Emer Cooke, EMA executive director, added that we need to use “all vaccines available to us” to beat this pandemic, pointing out that the risk from the mortality of COVID is much greater than the risk of what she said were “rare side effects”.
“Vaccines will help us in the fight against COVID and we need to continue to use these vaccines,” she said.
Asked whether countries should consider prioritising other available vaccines for women under the age of 60, Straus said that this was up to national governments.
“We have tried to provide the information we have to the best of our knowledge. Based on that information, national vaccination authorities can make up their mind on who they’d like to vaccinate with which vaccine,” she said.
The EMA will continue to look into the matter and will update information as required, the agency added.
[Edited by Zoran Radosavljevic]