Omicron blunts immune response more, say reports

Three studies were based on Pfizer’s mRNA vaccine

Updated - December 09, 2021 09:40 am IST

Published - December 08, 2021 11:06 pm IST - NEW DELHI

Photo used for representational purposes only. File

Photo used for representational purposes only. File

A slew of laboratory studies suggest that Omicron dramatically blunts the immune system’s response to the coronavirus in those inoculated with the Pfizer vaccine, more than any other variant so far. Though the studies don’t dent existing vaccines’ claims at protecting against severe COVID-19 and death, they suggest that booster shots may be required to protect to keep antibody levels up, or vaccines may have to be updated to account for newer variants.

The three studies are out of South Africa, Germany and Sweden and they all independently tested how antibody numbers in those vaccinated with the Pfizer mRNA vaccine were influenced when exposed to the Omicron variant of the coronavirus. These are laboratory studies and are done by extracting plasma from the blood of vaccinated people and tested in petri dishes. Some of them had previously been infected with the coronavirus. The researchers also studied if the antibody levels in those previously infected and vaccinated differed from those who had antibodies solely as a result of vaccination.

The first study out of Durban showed a nearly 40-fold decline in neutralising antibodies when blood plasma of those vaccinated and with a previous infection (with the original Wuhan strain) were tested against the Omicron variant. Another study out of Germany’s Institute of Virology found a 37-fold decrease in neutralising antibodies. This time, the comparison was in those previously infected with the Delta variant and vaccinated and when compared to the Omicron variant. The final study out of the Karolinska Insitute in Sweden showed the reduction in neutralisation with Omicron was seven-fold, which is significantly lower than observed in previous studies.

A key difference in the Swedish study was that they used a pseudo virus for their analysis, as opposed to the other two studies that employed a live virus and therefore a more realistic picture of how the virus might behave in the body.

By comparison, earlier studies on the neutralisation reduction by the Beta and Delta variant have shown they reduced antibodies no more than three-fold and this therefore puts Omicron in an entirely different league. Alex Sigal, Faculty at the African Health Research Institute, who led the study, tweeted that despite the fall in neutralisation, the results were “better than expected”. This was because the results suggested that those previously exposed to the virus and double vaccinated “retained a considerable level of immunity”, and that it showed Omicron continued to rely on well understood tactics to infiltrate the body’s defence.

Ben Murell, who was involved with the study at the Karolinska Institute, tweeted that while the magnitude in his lab’s results and that from South Africa differed “...what is common is that neutralisation is not completely lost for all samples, which is a positive”.

An independent expert told The Hindu that while the fall in antibodies represented by Omicron was significant, it wasn’t necessarily an indicator of a vaccine’s declining effectiveness. mRNA vaccines — the Pfizer and Moderna vaccines used this technology — were known to spike the neutralising antibody response much more than ChAdOx1 (or Covishield) and more than what’s required for protection, said Ram Thiruvengadam, a physician-scientist who researches the potency of vaccines. The fall in antibodies was also much steeper in mRNA vaccines and so, it’s important to conduct such studies in India, where a high fraction of people have already been exposed to the virus and were primarily inoculated with Covishield.

“The question here is, after the fall, are they at levels sufficient enough to confer protection? That answer isn’t here in these studies,” Dr. Thiruvengadam said.

Some studies showed that if the antibody levels in those vaccinated were at least 20% as much as in the levels in those infected by the virus, or those who were convalescent, that would indicate a sufficient protective effect. “Ideally, these [three] studies should have compared the antibody levels to those in the convalescent,” he added.

The studies also did not evaluate the T-cell response or the second, more critical line of defence employed by the body when it generates relevant antibodies when exposed to a live virus. The T-cell response can only kick in the following vaccination or a previous exposure to the vaccine.

Anurag Agrawal, Director, Council of Scientific and Industrial Research-Institute of Genomics and Integrative Biology (CSIR-IGIB) tweeted: “As expected, infection + vaccination neutralised Omicron. Such hybrid immunity also blocked super-mutated artificial spike protein earlier. We need such data for our population too to be sure this isn’t limited to mRNA vaccines.”

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