Booster shots may be useful even among highly vaccinated populations to reduce Covid transmission, especially given the prevalence of the Delta variant, scientists have said.
No decision has yet been made on booster jabs for routine use in the UK amid a debate over the pros and cons of implementing such a strategy. The Guardian understands it will be announced next week at the earliest, though could take longer.
On Thursday, scientists including Prof Neil Ferguson suggested that even if evidence did not yet show waning protection in the double-vaccinated against serious illness and death, booster shots could work to reduce the spread of cases.
High numbers of cases increase the risk to unvaccinated or otherwise vulnerable people, and could lead to the emergence of new variants.
Last week, there were an average of more than 33,750 daily cases across the UK compared to less than 1,400 at the same time last year – before the rise of the highly infectious Delta variant and before all restrictions had been eased – and 61,000 at the peak in January. With nearly 80% of UK adults having received two vaccine doses, hospitalisations and deaths are far lower than at their peak.
Many rich countries with strong vaccine coverage have announced the rollout of third shots amid concerns about waning immunity.
Preliminary data shows that people experience a fall in antibody levels weeks and months after getting their jabs, but so far the fall does not appear to have reduced protection against severe disease and death. In general, there is little scientific consensus on what level of antibodies and other tools in the immune system’s armament confer protective immunity.
However, boosters might work to prevent more infections and transmission, suggested Helen Petousis-Harris, a vaccinologist from the University of Auckland. “Because in order to prevent that infection, we really need the presence of these antibodies and if they’ve waned that might make establishing an infection more easy.”
UK data suggests somebody who is double-vaccinated is about half as likely to be infected as someone who is unvaccinated, and although the double-vaccinated person is far less likely to develop severe disease, they can still infect others.
“The other thing is boosters could help improve immunity to variants, and people who might not have responded so well at the beginning to the primary doses might also benefit from a booster,” Petousis-Harris added. “It’s likely that these things will contribute to the overall community immunity.”
Israel, for instance, has already kicked off its booster programme. “I think in Israel, they actually want to suppress transmission … if you have even 10% of your population unvaccinated, then one way of reducing risk to them is by boosting the immunity of everyone else,” said Ferguson, an epidemiologist at Imperial College London.
“I think the UK is adopting a much more incremental approach – so at the moment our joint committee on vaccination (JCVI) is only recommending boosters [third shots] for clinically extremely vulnerable people, which is only about 1% of the population.”
Booster shots for those with weak immune systems, who may not have mounted a good response to the first two jabs, is a way to keep the most vulnerable safe, World Health Organization Europe head, Hans Kluge, suggested earlier this week.
However, many scientists have also underscored that rich nations should not hoard vaccine supplies for third shots while some poor countries have not even been able to administer first shots to the most vulnerable.