A study has found that after Covid vaccine, care home residents' immunity declines steeply, leading to calls for regular boosters for the most vulnerable.
Protection against hospitalisation and death fell by one-third three to seven months after vaccination, according to a study of more than 15,000 care home residents. Protection against severe illness appears to be robust, but the decline is much sharper than that seen in younger people.
Prof Laura Shallcross, a public health expert at University College London, said that they are at increased risk of infections, hospitalisation and death as immunity fades.
She said it suggests annual boosters in residents may not be enough.
Adults over the age of 75 and residents in care homes will be offered a second booster in April. The health secretary, Sajid Javid, said this week that there could be more boosters in the autumn.
The findings published as a preprint could have an influence on the decision. The UK Health Security Agency funded the Vivaldi study, which monitored Covid in 331 care homes across England from December 2020 to December 2021.
The researchers found that two vaccine doses were effective at preventing 85% of hospitalisations and 94% of deaths among care home residents between two and 12 weeks after the second dose. At three to seven months after vaccination, the protection fell to less than half.
The trajectory of the staff who were tracked in the study was very different. After three months, protection against infections fell from 50% to 42% for staff with an average age of 45. There was no evidence of waning immunity against severe disease for staff.
The residents were given a booster in the autumn and the protection against hospitalisation was increased to 98%. Early data shows that protection fades in a similar way.
Shallcross said that elderly care home residents may need booster jabs in the future.
Shallcross said that if Covid follows a seasonal pattern, it may make sense to give people an autumn booster ahead of a winter surge. In the next year or two, Covid will not settle into a regular seasonal pattern, and there are likely to be erratic spring and summer waves of infections.
Shallcross said that while vaccine coverage in care homes was very good, there was a concern that elderly people in the community might underestimate their continued risk from Covid.
The emergence of the Omicron variant underscored the need for further protection even in younger age groups, according to Prof Danny Altmann, an immunologist at Imperial College London who was not involved in the work.
The hope is that a next generation of vaccines will produce much longer lasting immunity, meaning that repeated boosters will not be necessary.
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