An Israeli study by E.G. Levin et al titled “Waning Immune Humoral Response to BNT162b2 Covid-19 Vaccine over 6 Months” was published on October 6.
The study included 4,868 Pfizer-vaccinated healthcare workers over a period of 175 days. Not all were tested throughout the entire period. The two tests were for IgG antibodies and neutralizing antibodies.
The highest titers after the receipt of the second vaccine dose (peak) were observed during days 4 through 30, so this was defined as the peak period.
That is to be expected.
A substantial reduction in the IgG level each month, which culminated in a decrease by a factor of 18.3 after 6 months, was observed. Neutralizing antibody titers also decreased significantly, with a decrease by a factor of 3.9 from the peak to the end of study period 2 [day 70], but the decrease from the start of period 3 [day 71] onward was much slower, with an overall decrease by a factor of 1.2 during periods 3 through 6 [days 71–175].
In other words, there is already a significant drop of neutralizing antibodies—a factor of 3.9—after merely two months of receiving the second dose with a relatively slower decline from that point onwards.
As a comparison, the study mentioned the MMR vaccine:
Published work about many vaccines, such as those against measles, mumps, and rubella, has shown a small decrease each year of 5 to 10% in the neutralizing antibody levels.
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