The evidence has become clearer that people with weak immune systems may need top-up Covid-19 vaccinations to maintain their protection, the European Medicines Agency (EMA) has said.
"People with severely weakened immune system may need an additional dose as part of their primary vaccination," according to the agency's vaccine strategy chief Marco Cavaleri.
Data from the United States has also shown an increased number of adolescents are being admitted to hospital due to Covid-19 as the highly infectious Delta variant tears through unvaccinated groups, Dr Cavaleri warned.
“What we are seeing also emerging from the United States with the Delta variant spreading around, is that there is a massive increase in hospitalisation [of adolescents] due to the Delta variant, which affects mainly adolescents who are not vaccinated,” he said.
At present the messenger RNA vaccines by Pfizer and Moderna are approved for use in the EU for people aged 12 and over. The EMA is set to assess evidence from trials of the use of the vaccines in the five to 11 age group in the coming weeks.
The agency is also evaluating an application by BioNTech-Pfizer to approve the use of a third booster dose of its Comirnaty vaccine in the general population, to be taken six months after their second shot, to ensure protection remains high.
Current evidence shows that there remains “considerable protection from severe disease and hospitalisation in the general population” after two doses, Dr Cavaleri said.
But he acknowledged that national authorities may go ahead and begin offering booster doses to vulnerable people before the EMA’s assessment has concluded, and said this was “understandable” given the situation.
“An increase in breakthrough infection has been reported in different parts of the world due to the Delta variant,” Dr Cavaleri said.
“In light of these trends, whether certain vulnerable groups might benefit already now from booster vaccination is under discussion in most of the European member states,” he added.
“EU member states through their national immunisation advisory . . . may proceed anyway with plans to administer additional or booster doses as a proactive measure to protect public health before a regulatory decision can be taken. Such decisions are very well understood by the agency in the emergency context that we are going through.”
The World Health Organisation (WHO) has lambasted wealthy countries for moving towards administering booster doses to the fully vaccinated while low and middle-income countries face shortages.
The body's chief scientist, Soumya Swaminathan, said this week that there are about 10,000 deaths a day from Covid-19 that would be "entirely" preventable if vaccines were shared equally.
“I am very concerned that some countries are talking about boosters when there isn’t a lot of evidence that vaccines are failing to protect people from severe disease,” Dr Swaminathan said.
By the end of September, the WHO expects there to be enough vaccines to cover all healthcare workers and elderly people globally, if shared equally, something which would significantly cut the number of deaths in the pandemic.
The EMA has been able to “to scale up vaccine production very significantly” during the summer by granting authorisations to extra vaccine manufacturing and fill and finish sites, Dr Cavaleri said.
Overall, more than 70 per cent of adults in the European Union have now been vaccinated, according to national statistics collected by the European Commission, but rates differ sharply around the continent with only a minority vaccinated in countries like Bulgaria and Romania.