Covid vaccines prevent less than one in 10 infections six months after they are administered, a study has found.
New Zealand researchers came to their conclusion after assessing data from over 5million people from December 2020 when the jabs were first deployed in the country to February last year.
Of these, 4million were vaccinated, and about 1million never got a Covid vaccine, with jabbed persons being matched by age and sex to an unjabbed counterpart.
Scientists then assessed the jabs effectiveness against a variety of different Covid outcomes, including against infection, hospitalisation and death, using patient data.
Publishing their findings in the New Zealand Medical Journal, the researchers assessed outcomes based on people getting the second Covid booster.
New Zealand researchers came to their conclusion after assessing data from over 5million people from December 2020 when the jabs were first deployed in the country to February last year
While the jab was found to offer sustained protection against deaths from the virus, protection against infection was found to drop off dramatically.
In the first month people got the jab it was found to stop 57 per cent of infections. But this dropped off to just 9.9 per cent six months later.
Jab-based protection against becoming hospitalised due to Covid was better, though a significant dropoff was also recorded.
Vaccinated persons enjoyed an 82 per cent protection against hospitalisation with the virus in the first month after getting it. But this declined to just 49 per cent by month six.
The authors noted that as there were no Covid deaths in the vaccinated cohort who got the second booster a comparative analysis on this outcome wasn’t possible.
This is not the first study to have found Covid vaccines decline in effectiveness over time.
The exact figure depends on the stage of the global pandemic, what variant was circulating at the time, and can also vary by brand.
One American study in 2021 found Covid jabs used in the US fell from 85 per cent effectiveness against infection to some 50 per cent in six months.
A Qatari study, again from 2021, even found Pfizer’s Covid jab was only 20 per cent effective at stopping people getting infected after six months.
Covid vaccines, which brought an end to the paralysing lockdowns, lose their protective power due to two factors.
Firstly, the initial flood of antibodies designed to target the Covid virus which are produced by the body fades over time, though experts say some longer-term protection persists.
Secondly, the virus itself evolves over time, new variants evolve with slight differences that mean they are better able to dodge the protection jabs, which were designed to combat older strains of Covid, offer.
This is why updated jabs, designed to target new, now more widely circulating, strains of the virus have been used in subsequent Covid booster campaigns.
In the first month the jab was found to stop 57 per cent of infections among Kiwis that got it. But this dropped off to just 9.9 per cent six months later
The phenomenon of waning protection isn’t unique to Covid either, its why some people, such as the elderly and health workers, are offered a new flu vaccine each year designed to target the new versions of the virus that are spreading.
It should also be noted the same basic problem occurs with natural immunity from Covid infection, with this protection also waning over time.
The authors said that while their study strengthened by its large number of participants and reliable public backed data it did have a number of limitations.
One was due to declining numbers of unvaccinated people could have influenced the results leading to a potential over underestimation of the vaccine’s effectiveness.
Another was they were unable to track the specific brand of Covid vaccine jabbed people received, meaning any differences by this metric couldn’t be measured., though they noted the majority of people received Pfizer’s jab.
Additionally, the authors said there were unable to distinguish between different Covid variants given the dominance of the Omicron variant over the majority of the study period.
They said future studies, both tracking the effectiveness of the jabs beyond six months, and differences in outcomes by vaccine type and Covid variant were warranted.
