The effectiveness of a booster dose of vaccine against symptomatic COVID-19 in people over 50 is more than 93%, regardless of which vaccine was given as first and second dose, according to research released today by the UK Health Security Agency.
The findings come as the Government announces that booster doses will now be offered to those aged 40 to 49 who had their second dose more than six months ago. 16 and 17 year- olds are now also being encouraged to come forward for a second dose.
Boosters will continue to be offered as a dose of either the Pfizer vaccine or a half dose of the Moderna vaccine.
Over 12 million people in the UK have now been given a booster dose, which until today were being offered to those aged 50 and over, front-line medical staff and people with certain health conditions that increase their risk of severe illness.
The study published today as a preprint (and therefore not yet peer-reviewed) was undertaken by researchers from Imperial College London and the London School of Hygiene and Tropical Medicine. It compared the effectiveness of a booster dose of the Pfizer vaccine against symptomatic infection in those over 50 at various time intervals, compared with the following groups:
- people who had had their second dose at least 140 days prior, but who hadn’t had a booster dose
- unvaccinated individuals
The researchers separated out results according to whether people had previously received AstraZaneca or Pfizer, and excluded cases where people had received two different vaccines as their primary course.
After 14 days, the ‘absolute effectiveness’ (meaning effectiveness compared to unvaccinated individuals) of a booster dose against symptomatic disease was found to be 93% in people who previously had the AstraZeneca vaccine and 94% in those who were given the Pfizer vaccine as their primary doses.
In contrast, the absolute effectiveness of two primary doses of either the AstraZeneca or Pfizer vaccine after 20 or more weeks was shown to be 44.1% and 62.5% respectively, demonstrating the waning of effectiveness over time and the importance of booster doses to ensure that people are protected.
Commenting on the findings, Dr Michael Head, Senior Research Fellow in Global Health at the University of Southampton, said:
Administering a third dose shows a very strong immune response, and the emerging UK data shows that there is 93% protection against symptomatic infection. Protection against severe COVID-19 illness will be even higher than that. Similar findings are coming from other countries that have an advanced booster programme, such as Israel. This is an excellent outcome and indicates that the advice to offer booster doses to the over 40s is a good move. A winter of COVID-19 and flu brings huge uncertainty around the potential impact on those infections upon the health service, so the more immunity we can build up now, the better.
Given the waning of immunity around 6 months after initial immunisation, it may be that the longer-term outcome is to regard COVID-19 vaccination as a three-dose schedule, rather than 2 doses and a booster when necessary. There are other example of three-dose immunisations. In the UK, these include the meningitis B vaccine, and also the ‘6 in 1’ vaccine.