Does Covid vaccine protect against Omicron variant? Efficacy of Pfizer, Moderna and AstraZenca jabs explained

The Pfizer and Moderna vaccines give the most significant boost to immunity levels when used as a third dose

Booster vaccines will likely offer good protection against the OmicronCovid-19 variant, a new study suggests.

A team of scientists working on the CovBoost study, published in The Lancet, said protection from third doses could protect against hospital admission and death.

The study assessed the effects of booster doses on the body’s T cell immune response and it is thought that current vaccines could help to fend off the new variant, which is feared to be more transmissible than other strains.

How effective are the vaccines against Covid-19?

Six vaccines were tested as third doses in the study, including AstraZeneca, Pfizer, Moderna, Novavax, Janssen (made by Johnson and Johnson) and CureVac (which has ceased production).

It was found that both the Pfizer and Moderna mRNA vaccines led to the most significant rise in immunity levels when used as a booster dose.

The findings support the decision to rely on these vaccines for booster doses.

When looking at antibody levels in the trial, people who received two doses of AstraZeneca initially had booster responses that were between 1.8 times higher to 32.3 times higher depending on the booster vaccine used.

After two doses of Pfizer, the range was 1.3 times higher to 11.5 times higher.

However, researchers said these ratios should be interpreted with caution as they relate to immune response rather than real-world protection against disease.

Professor Saul Faust, trial lead and director of the NIHR Clinical Research Facility at University Hospital Southampton NHS Foundation Trust, said: “All of the vaccines in our study do show a statistically significant boost… RNA (Pfizer and Moderna) very high, but very effective boosts from Novavax, Janssen and AstraZeneca as well.”

Prof Faust added that the vaccines worked well against existing variants, although Omicron was not tested in the study.

However, scientists believe that T cell immunity – which was studied alongside antibodies in the research – could play a significant role in fending off the variant.

T cells work alongside antibodies in the immune system to target viruses.

Prof Faust explained: “Even though we don’t properly understand its relation to long-term immunity, the T cell data is showing us that it does seem to be broader against all the variant strains, which gives us hope that a variant strain of the virus might be able to be handled, certainly for hospitalisation and death if not prevention of infection, by the current vaccines.

“Our hope as scientists is that protection against hospitalisation and death will remain intact.”

Samples from the study, which involved 2,878 people aged 30 or over receiving a booster 10 to 12 weeks after their initial two doses, have now been passed to the UK Health Security Agency (UKHSA) to look at how well the Omicron variant can be neutralised by vaccines.

Were there any side effects?

All seven vaccines did not pose any safety concerns, with fatigue, headache and sore arm reported as the most common side effects.

Jonathan Ball, professor of molecular virology at the University of Nottingham, said of the findings: “The data clearly shows that all boosters provided a lift to at least one aspect of your Covid immunity, and that side effects were, on the whole, mild.

“The data also shows that an mRNA booster – such as Moderna or Pfizer – provided the best overall boost, irrespective of whether your first doses were mRNA or (AstraZeneca).

“The fact that the mRNA vaccine boosts gave a marked increase in both antibodies and T cells is great news, especially now, when our attention has been grabbed by the emergence of the Omicron variant.

“We still don’t know how this increase in immunity translates into protection, especially against serious disease, but I am still convinced that our vaccines will continue to provide the protection that we need.”

Which vaccines are being used as boosters?

The Pfizer, Moderna and AstraZeneca vaccines have all been approved for use as a booster by the Medicines and Healthcare products Regulatory Agency (MHRA).

However, the Joint Committee on Vaccination and Immunisation (JCVI) has recommended only using the two mRNA vaccines (Pfizer and Moderna) where possible, as these have been proven to have fewer side effects and a stronger immune response.

Those eligible for the booster will be offered either a full dose of the Pfizer vaccine, or a half dose of the Moderna vaccine, regardless of which jab individuals had for their first two doses.

In cases when neither of these vaccines can be offered, due to an allergy for example, the JCVI advises that the AstraZeneca vaccine can be used for those who received this jab for their first and second dose.

Professor Mark Woolhouse, member of the Scientific Pandemic Influenza Group on Modelling (Spi-M), said that vaccinations will be “very, very good” against the Omicron variant and boosters will help to protect against hospitalisation and severe disease.

He told the BBC’s Andrew Marr Show: “Vaccinologists and immunologists think that this variant won’t evade the vaccines entirely.

“It’s important to remember that against the Delta variant, which is a different variant, the booster vaccinations have turned out to be very effective, well into the 90% protection against infection but also against disease and putting people in hospital.

“So even if the vaccines were slightly less effective against Omicron they would still be very very good.”

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