This article is part of our special report From vaccine race to marathon: What’s next for coping with COVID?.
The EU seems to be comfortable with betting on mRNA COVID vaccines for now. But just around the corner, vaccines developed under other platforms are lining up, with recombinant proteins and the whole virion-inactivated vaccines leading the way.
There are four COVID vaccines authorised in the EU at the moment: mRNA vaccines such as Comirnaty or Spikevax, developed, respectively, by Pfizer/BioNTech and Moderna, and adenoviral vector vaccines – Oxford’s Vaxzevria and the single-shot Janssen by Johnson&Johnson.
The EU vaccination strategy is heavily relying on mRNA vaccines. The Commission recently signed the world’s largest contract for COVID-19 vaccines contract with Pfizer/BioNTech, which foresees the delivery of 1.8 billion doses of vaccines between the end of the year and 2023.
Contacted by EURACTIV, a European Commission spokesperson explained that the focus should be on technologies that have proven their worth and mRNA vaccines are a clear case in point.
But vaccine developers are already working with new vaccine platforms.
The EU European Medicines Agency (EMA) is in contact with slightly over 30 developers of potential COVID-19 vaccines and running a rolling review of four potential COVID-19 vaccines.
Based on the World Health Organisation landscape of candidate vaccine development, there are more than 100 vaccines in clinical development worldwide, dominated by protein-based subunit vaccines.
“The main types of vaccine we’re going to see coming through next are these recombinant proteins and the whole virion inactivated vaccines,” Adam Finn of the European Technical Advisory Group of Experts on Immunisation (ETAGE), who is also chair of paediatrics at the University of Bristol, told EURACTIV.
These two platforms, he added, “are much more traditional” and might be entering the vaccination campaigns already in the upcoming months.
“There are a whole lot of other more experimental platforms. And it’s quite hard to get information about those because very often the developers are quite secretive about what they’re doing,” said Finn.
Protein-based subunit vaccines getting ready for vaccination marathon
The Commission spokesperson said that protein-based subunit vaccines were also recommended for use by scientific experts, in addition to mRNA vaccines.
These vaccines should be cheaper as they can be transported at higher temperatures than mRNA vaccines.
“It’s a very well-established technology now. It’s been around for about 30 years. The most prominent example of this technique is the hepatitis B vaccine,” said ETAGE’s Finn.
“In principle, it ought to be a much easier, more straightforward way to make vaccines than either of the new technologies where the manufacturing bases have to be set up from zero,” he said.
The cheaper price and large quantities, together with emerging evidence of their effectiveness, should boost the popularity of this type of vaccine. Another factor is the safety of the new platforms used for COVID-19 vaccines.
“There are emerging rare but serious, or potentially serious, safety signals with new platforms, which is interfering with the political will to use them,” Finn said.
‘Mix and match’ could keep the vaccination rolling
These new COVID-19 vaccines might be the ones that join the ‘mix and match’ or heterologous vaccination strategy already seen in some member states.
In a joint update released on Wednesday (14 July), the EMA and the European infectious disease agency (ECDC) noted that experts responsible for the vaccination programmes in more than a half of member states have decided, with a view to their national situations, to use different vaccines for the second dose from the ones used for the first.
In a heterologous vaccination strategy, which has already been applied for some other vaccines, a different vaccine is given for the second dose in a recommended 2-dose schedule. This may allow quicker vaccination strategy rollouts.
“Perhaps the most compelling reason for mixing and matching is that it gives you flexibility in terms of supply,” explained Finn, pointing to situations where health authorities have been giving a particular vaccine to the population and then cannot get any more of it.
While preliminary results from studies in Spain, Germany, and the UK suggest a satisfactory immune response and few safety concerns, EMA and ECDC are still refraining from issuing a definitive recommendation to use different COVID-19 vaccines for the two doses.
In Finn’s opinion, using different vaccines is a “quite good idea”.
“The positive side is that there may be an advantage to presenting the same antigen to the immune system in a different way, in the sense that that may stimulate either a bigger response or a broader response than just using the same hit all the time,” he said adding, however, that it is not yet clear how those better responses turn into better protection.
[Edited by Zoran Radosavljevic]