How quickly does protection decline after Pfizer’s COVID-19 vaccine? – Community News
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How quickly does protection decline after Pfizer’s COVID-19 vaccine?

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A new study examines the declining protection of the Pfizer vaccine over 180 days. photo alliance/Getty Images
  • Researchers examined whether immunity to COVID-19 wanes after receiving a second dose of Pfizer-BioNTech mRNA vaccine.
  • They found that the more time that elapses after the second vaccine dose, the more likely individuals are to contract a SARS-CoV-2 infection.
  • While their results may justify booster vaccines for immunocompromised individuals, they caution that further research is needed because they have not used blood tests to monitor participants’ immune responses over time.

Protection against COVID-19 comes from contracting the SARS-CoV-2 virus and recovering or vaccinating.

Research has shown that those who contract SARS-CoV-2 6 months after infection have 85% protection against symptomatic disease.

Meanwhile, as the authors of the recent study explain, “vaccination has been reported to be 50-95% effective at various times.”

Over time, the immune system responds to SARS-CoV-2 decreases, meaning those who have recovered from the virus or who have been vaccinated may be less protected over time.

In a recent study, researchers from Israel and the United States conducted a study to investigate whether protection against infection decreased over time after a second dose of the Pfizer-BioNTech mRNA vaccine.

They found that 90 days after a second dose of Pfizer, individuals had an increased risk of contracting SARS-CoV-2. The findings appear in the BMJ.

“Israel was one of the first countries to successfully roll out a vaccination campaign to the population, so we were also among the first to observe the declining effect of the vaccination as time passed since the first two injections of the vaccine,” Dr. . Ariel Israel, Ph.D., one of the authors of the study, said: Medical news today.

“Our study is an observational study designed to evaluate whether the protection provided by the Pfizer vaccine decreases over time with the degree of positive [reverse transcription-polymerase chain reaction (RT-PCR) for SARS-CoV-2] in people vaccinated at different times before the test.”

“We saw that after the excellent protection that the vaccine provided in the first 3 months, there was a gradual increase in the infection rate,” explains Dr. Israel out.

The researchers collected medical records from Leumit Health Services, a major healthcare provider in Israel that serves 700,000 people across the country.

For their analysis, they used health records from individuals 18 years of age and older who underwent SARS-CoV-2 RT-PCR testing between May 15, 2021 and September 17, 2021, after receiving two doses of the Pfizer vaccine.

The team performed tests at least 3 weeks after their second vaccination. They divided the participants into three age groups to reflect the different stages of the vaccine rollout:

  • 60 years and older
  • 40-59 years
  • 18-39 years

They also divided the time between the second vaccination and RT-PCR testing into 30-day intervals after the first 90 days, with the latter category being designated as 180 days or more since the second vaccination. In total, the researchers analyzed health records of 83,057 individuals.

Their analyzes accounted for potential confounding risk factors for SARS-CoV-2 infection, such as age, gender, socioeconomic status, and pre-existing health conditions.

Of the researchers surveyed, 9.6%, or 7,973 people, had a positive test result. The mean time between the second vaccine dose and an RT-PCR test was 164 days.

The team found that the more time that had passed since the second vaccine, the more likely people were to get SARS-CoV-2.

While 1.3% of participants got a positive test result 21-89 days after their second vaccine, the same was true for 2.4% of people at 90-119 days, 4.6% at 120 days149 days, 10.3% after 150179 days and 15.5% after 180 days.

These results translated into a 2.37-fold higher chance of contracting the virus after 90 days from the second vaccination and a 2.82-fold higher chance after 150 days or more.

They also found that two injections 21 days apart offered more protection than one and that changes in the immune system related to age affected the immune response to the vaccines.

dr. Israel explained that the reasons for declining immune protection are “beyond the scope of their investigation.” However, he suggested some possible mechanisms:

“The most likely explanation is that antibodies, as well as immune system cells that produce antibodies or kill cells.” [with the infection], have a limited lifespan, so their numbers gradually decrease after the initial reaction caused by the vaccine.”

“[Fewer] antibodies in the blood, and [fewer] cells that can kill the virus mean that the virus is more likely to evade the immune system in the early stages of infection, and this is probably why we observe an increased rate of positive PCR in individuals who have been previously vaccinated,” he added. he to it.

The researchers concluded that immunity to SARS-CoV-2 decreases after a second Pfizer vaccine after the first 90 days and that a third vaccine or booster dose may be warranted for immunocompromised individuals.

They also note some limitations to their research. Because of the observational study design, they say they may not have explained all contributing factors, which may have biased their results.

For example, they note that they only included individuals who chose to request an RT-PCR test for SARS-CoV-2 and that some may have had different thresholds for requesting a test.

They also noted that previously vaccinated individuals may have had different distancing habits than those vaccinated later, which could have significantly affected their level of risk.

In addition, the researchers note that RT-PCR tests were not followed by blood tests, meaning they cannot be sure that immunity has indeed declined.

“In light of these results, public health authorities in Israel have recommended booster injection for all age groups, and we have observed a subsequent dramatic reduction in the incidence of COVID-19 immediately after the booster injection rollout,” said Dr. Israel.

“It is too early to say for sure how long the protection would last after the booster injection. We will continue to monitor the infection rate and will report our data if we see a reduction in booster protection,” he concluded.

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