A newly-released Israeli study shows that immunity after being vaccinated for the coronavirus Delta variant diminishes over time for all age groups a few months after receiving the second dose.
Starting in December 2020, Israel carried out a speedy vaccination campaign using the Pfizer vaccine. Within three months more than half of the population had been fully vaccinated. Alongside various social health measures, the high vaccination rate led to a sharp curtailing of the outbreak and by May there were only a few dozen cases identified each day.
But by June, numbers started to rise again and by the end of the Summer, daily identified infections reached over 10,000 cases – including a substantial number reported in vaccinated persons. This led to an increase in severe cases and deaths among both the vaccinated and unvaccinated populations.
The study analysed the infection rate and the number of serious cases amongst those that had been vaccinated, according to the different vaccination periods that the shots were administered.
From a total of 5.28 million adults that were fully vaccinated, data for 4.71 million was analysed. Researchers found that 13,426 vaccinated persons had still contracted the coronavirus. Of these, 403 were severe cases.
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The researchers conclude that immunity from the vaccine decreases over time, either because of the emergence of new variants or simply due to the effect of the vaccine's protection wearing off.
However, even with this diminishing immunity, the non-vaccinated were much more affected by severe Covid-19 complications.
In July, Israel’s health ministry approved the roll-out of a third booster dose to persons who had taken their second dose at least 5 months earlier, starting with older age groups before opening to the rest of the population. Cases have since dropped and now average in the few hundreds per day.
It is currently unclear how long the strengthened immunity from a booster shot lasts. An earlier Israeli study showed that the likelihood of those over 60 contracting the virus dropped 11 times and 19 times to get seriously ill, after having the booster shot.