‘AstraZeneca shots, booster effective against Omicron’
The findings hold significant implication for India, where close to 90% of the 1.4 billion doses are of Covishield
People who took AstraZeneca vaccines may be at a comparatively lower risk of needing to go to a hospital if they have been infected with the Omicron variant than those who took the mRNA vaccines, an early analysis of infection trends in England has suggested.
A booster dose of the vaccine, which marketed as Vaxzevria globally and also manufactured and administered in India as Covishield, is also capable of triggering an improved antibody response, the company said separately on Thursday.
The findings hold significant implication for India, where close to 90% of the 1.4 billion doses are of Covishield.
An analysis by researchers at the Imperial College of London found there was a lower risk, when compared to Delta variant infections, of people with Omicron needing to go to a hospital when they were fully vaccinated with the AstraZeneca vaccine than when they took either the Moderna or the Pfizer-BioNTech vaccines.
“Most intriguing is an apparent difference between those who received AstraZenca (AZ) vaccine versus Pfizer or Moderna (PF/MD) for their primary series (doses 1 and 2). Hazard ratios for hospital attendance with Omicron for those who received PF/MD as their primary vaccination schedule are similar to those seen for Delta in those vaccination categories, while Omicron hazard ratios are generally lower than for Delta for those who received AZ as their primary vaccination,” the report said, with the caveat that these were still early numbers.
Experts said this could be because the AstraZeneca/Covishield vaccine produces a more robust cellular immunity – the more common measure of immunity is by accounting for antibodies, or humoral immunity – when compared to the others. “The AZ vaccine is known to induce better cellular (T cell) responses than the RNA vaccines; the latter induce higher titre neutralising antibodies. So, while the RNA vaccines would give better protection from infection and transmission, the AZ vaccine should protect better from severe disease. A University of Birmingham study showed this in people 80 and older. The older age group is also the one that shows more severe disease. This could be an explanation for the Imperial College observation,” said virologist Dr Shahid Jameel, research fellow at Green Templeton College, Oxford University.
Separately, the company released data on how its boosters performed in lab analysis of antibody responses. “Neutralisation titres for Omicron were boosted following a third dose with Vaxzevria compared to titres after a second dose. The levels seen after the third dose booster were higher than the neutralising antibodies found in individuals who had been previously infected with and recovered naturally from COVID-19 (Alpha, Beta, Delta variants and original strain),” said AstraZeneca in a statement.
Two doses of Vaxzevria have been associated with protection against the Delta variant in real world studies, but appeared to offer no protection against infection when compared to Omicron.
It is important to note that the Imperial report relates to risk of needing a hospital visit.
“It is very encouraging to see that current vaccines have the potential to protect against Omicron following a third dose booster. These results support the use of third dose boosters as part of national vaccine strategies, especially to limit the spread of variants of concern, including Omicron,” said John Bell, Regius professor of medicine, University of Oxford, UK, who is also one of the study investigators.
“Vaxzevria plays an important role in vaccination programmes around the world and these data give us confidence that the vaccine should be given as a third dose booster. It is also important to look beyond antibodies to better understand how vaccines offer protection against Omicron. As we better understand Omicron, we believe we will find that T-cell response provides durable protection against severe disease and hospitalizations,” said Mene Pangalos, executive vice president, BioPharmaceuticals R&D, AstraZeneca.
Experts in India have also been in favour of giving booster anti Covid-19 vaccine dose to those at high risk.
“For subsets (immunocompromised), elderly, combormbities — it makes sense to protect them as much as possible. For the rest, who are generally healthy, timing and type of vaccine need data to back use,” said Gagandeep Kang, one of country’s top vaccine expert, and senior faculty at Christian Medical College, Vellore (Tamil Nadu).