Two doses of Covid vaccines induce lower antibody levels against Omicron: Oxford study


London: Two doses of Pfizer and AstraZeneca COVID-19 vaccines generate lower levels of antibodies to the Omicron variant of coronavirus, according to a study suggesting that those previously infected or vaccinated may be at increased risk of infection.

Researchers from the University of Oxford in the United Kingdom analyzed the effect of the worrying Omicron variant on one of the immune responses generated by vaccination.

The as-yet-peer-reviewed study, published on preprint repository MedRxiv on Monday, used blood samples from people who had previously received two doses of the AstraZeneca or Pfizer vaccines and a live virus isolate.

The researchers demonstrate a significant decrease in neutralizing titers – a measure of the level of neutralizing antibodies generated in response to vaccination against or infection from COVID-19.

The results indicate that the Omicron variant has the potential to drive a further wave of infections, including among those already vaccinated, the researchers said.

However, they noted that there is currently no evidence of increased potential for causing serious illness, hospitalizations or deaths in vaccinated populations.

These results are consistent with recently published data from the UK Health Security Agency showing reduced efficacy of two doses of these vaccines against symptomatic disease due to the Omicron variant compared to Delta.

However, this efficacy was improved with the third-dose vaccine, the researchers said.

“These data will help those developing vaccines and vaccination strategies determine the routes to best protect their populations, and push home the message that those offered booster vaccination should take it,” said Professor Gavin Screaton, head of Oxford’s Medical Sciences Department and lead author of the paper.

“While there is no evidence of an increased risk of serious illness or death from the virus among vaccinated populations, we must remain cautious as a greater number of cases will still place a significant burden on health systems,” Screaton said.

The researchers noted that this data is important but is only part of the picture.

They only look at neutralizing antibodies after the second dose, but do not tell us about cellular immunity, and this will also be tested using stored samples when the assays are available, they said.

“We have not yet assessed the effect of a ‘third dose’ booster, which we know will significantly increase antibody concentrations, and it is likely that this will lead to improved potency against Omicron variant, “said Matthew Snape, professor at the University of Oxford and co-author of the study.

“Vaccination induces many arms of our immune system, including neutralizing antibodies and T cells,” said Teresa Lambe, a professor at the University of Oxford and author of the paper.

“Real-world efficacy data have shown us that vaccines continue to protect against serious disease with past variants of concern. The best way to protect ourselves going forward in this pandemic is by getting vaccines in arms,” ‚Äč‚ÄčLambe added.

This story has been published from a telecommunications agency feed with no changes to the text. Only the heading has been changed.

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