New research has suggested that Covid protection from two doses of the Pfizer or AstraZeneca vaccines begins to wane within six months of being administered.
But how long does the Covid vaccine actually protect you and how does it vary between vaccines?
Here’s what you need to know.
How long does the Covid vaccine last for?
Analysis from the Zoe Covid study found that in a reasonable "worst-case scenario" protection could fall to below 50% for the elderly and healthcare workers by winter.
The study involved more than 1.2 million test results and participants, but the vaccines were not trialled against the now dominant Delta variant of the virus.
The Pfizer-BioNTech vaccine was found to be 88% effective at preventing Covid-19 infection a month after the second dose, but this decreased to 74% after five to six months.
Protection from the Oxford-AstraZeneca vaccine was found to fall to 77% just one month after the second dose, which then decreased to 67% after four to five months.
‘Waning protection is to be expected and is not a reason to not get vaccinated’
Professor Tim Spector, lead scientist on the Zoe COVID Study app, said that although waning protection is to be expected, the UK “urgently” needs to make plans for vaccine boosters.
He said: "In my opinion, a reasonable worst-case scenario could see protection below 50% for the elderly and healthcare workers by winter.
"If high levels of infection in the UK, driven by loosened social restrictions and a highly transmissible variant, this scenario could mean increased hospitalisations and deaths".
Prof Spector added that we "urgently need to make plans for vaccine boosters".
He added: "Waning protection is to be expected and is not a reason to not get vaccinated.
"Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to get fully vaccinated."
How effective is the Moderna vaccine?
At the beginning of August, Moderna - which is also being administered in the UK - said its Covid jab was about 93% effective through six months after the second dose, which shows little change from the 94% efficacy reported in its original clinical trial.
However, Moderna added that a booster dose will be necessary before the winter season as antibody levels are likely to wane.
Moderna Chief Executive Stéphane Bancel said at the time: "Our Covid-19 vaccine is showing durable efficacy of 93 percent through six months, but recognise that the Delta variant is a significant new threat so we must remain vigilant.”