The findings from the first lab studies to estimate how resistant the Omicron variant could be were published early on Wednesday, unanimously predicting what could be the biggest hit yet to the protection offered by coronavirus vaccines, although experts said fully vaccinated people may still have a substantially better chance of averting severe disease.
The findings are based on lab tests in which researchers expose a live virus or an engineered virus expressing the same mutations as the Omicron variant to antibodies drawn from people who were given doses or had a past infection, or both.
The first was from researchers in South Africa, where the variant of concern (VOC) has spread rapidly, leading to an unprecedented explosion in new cases. The scientists found there was a 41.4-fold drop in neutralisation ability overall, to the point that variant almost completely escaped the antibodies from most fully vaccinated samples. But, crucially, five out of six samples of antibodies from people who were fully vaccinated and had a past disease could neutralise the virus.
Two other studies, by separate teams of researchers based in Sweden and Germany, made similar findings, including a massive drop in neutralisation titers, which is calculated on the basis of concentration required for antibodies to neutralise the virus – the more concentration, therefore more antibodies, needed, the sharper is the drop in the titer.
A fourth study conducted by Pfizer and its subsidiary BioNTech too recorded a 25-fold drop in titers when antibodies from people with two doses were exposed to Omicron, but the deficit disappeared when antibodies from people with a third booster dose was used.
{{/usCountry}}A fourth study conducted by Pfizer and its subsidiary BioNTech too recorded a 25-fold drop in titers when antibodies from people with two doses were exposed to Omicron, but the deficit disappeared when antibodies from people with a third booster dose was used.
{{/usCountry}}What does this mean?
The studies confirm what immunologists were hypothesising seeing the unprecedented number of mutations in Omicron: the ability of past immunity, elicited either solely by vaccination or only by history of disease is likely to be significantly hampered in staving off an Omicron infection.
But crucially, the immune escape is only partial, not total, and that those with hybrid immunity – vaccinated as well as recovered from Covid-19 – are likely to have substantial protection. Hybrid immunity has long been regarded as a sort of gold standard of protection against the Sars-Cov-2.
Pfizer, in its statement, contends that its third shot offers significantly higher protection, although the study from Frankfurt university researchers appears to conclude that even with boosters, neutralisation titers show a significant drop.
Scientists also said that vaccine efficacy against severe disease and death is likely to remain reasonably high among all groups – those with a past infection, full vaccination, vaccination and infection, and boosted vaccination.
This is likely due to the activation of memory cells, particularly T cells, which can recognise the pathogen more broadly and are less affected by mutations in Omicron – something Pfizer alluded to in its statement.
“Although two doses of the vaccine may still offer protection against severe disease caused by the Omicron strain, it’s clear from these preliminary data that protection is improved with a third dose of our vaccine,” said Albert Bourla, chief executive of Pfizer. “Ensuring as many people as possible are fully vaccinated with the first two dose series and a booster remains the best course of action to prevent the spread of Covid-19.”
The four lab tests are still using small numbers of samples and must be seen as preliminary, and they do not signal whether the drop in vaccine efficacy will be in similar measure. Measuring neutralisation in lab setting is not a proxy for vaccine efficacy, but they do act as a correlate.
Implication for India
The high transmissibility of Omicron variant is a cause for concern for India as it is globally. India’s mainstay vaccines have also demonstrated lower efficacy across the board when compared to mRNA vaccines.
In late July, the Indian Council of Medical Research estimated that two out of every three Indians may have been exposed to the virus, translating to a high proportion of the general public likely exposed to an infection. As on December 8, the country has also delivered at least one dose to 86% of the adult population.
India, therefore, likely has a different immune profile to other countries, especially those where vaccine coverage and case rates have been low. A sizeable number of people may even have hybrid immunity.
But the findings from the studies published in the last 24 hours reinforce the need for a booster dose strategy in the country, particularly for the elderly population that was mostly covered in the first half of 2021. How Omicron spreads among children will also be of crucial implication for India, where no one under the age of 18 is eligible for a dose yet.