December 12: What more we know about Omicron
Late last week, the first real-world evidence arrived of how vaccine efficacy against symptomatic Covid-19 all but erodes in case of an infection with the Omicron variant
Late last week, the first real-world evidence arrived of how vaccine efficacy against symptomatic Covid-19 all but erodes in case of an infection with the Omicron variant.
An analysis of 581 symptomatic Omicron cases showed that two doses of the AstraZeneca vaccine (known as Covishield in India) offered no protection at all, while a regular course of the Pfizer-BioNTech shot was roughly 30% effective.
If boosted – the United Kingdom has largely used the Pfizer-BioNTech vaccine as boosters – the efficacy rates recovered to 71.4% for people who had an initial full course of AstraZeneca vaccines, and 75.5% for those with a full course of the Pfizer dose.
The case for boosters
Compared to Delta, the numbers from UK Health Security Agency (UKHSA) show a significant hit to vaccines and a significantly higher threat of household infection, secondary infections and reinfections.
Close to 20% of the people infected with Omicron went on to infect another household member – in contrast, this number was only 8.5% in case of Delta. In case of secondary infections, the attack rate rose almost twofold with the newest variant, and there was 5.2-fold higher risk of reinfection with Omicron.
Compared to the thousands of cases typically analysed, these numbers are preliminary, but they fit into a larger body of research that is now reaching an almost certain conclusion – boosters will be needed to adequately protect against the variant.
The second reason relates to the findings of a modelling study of how Omicron will lead to infections and deaths in the UK by researchers from London School of Hygiene & Tropical Medicine. The researchers, in their latest update, found that the uptake of booster shots has the most significant effect on keeping cases and infections low, followed by the speed of booster rollout, and the rate at which Omicron infections are introduced in the population.
Controlling all three factors naturally lead to the most optimistic scenario in terms of infections and deaths avoided.
The third factor has to do with India’s current vaccine stocks and the number of the most vulnerable people. India has close to 140 million people in the 60-plus age group, which is regarded the most vulnerable to Covid-19 and, according to government figures released on Sunday, there are more than 179 million “unutilised and surplus” doses available with states.
Avoiding red herring
From the scientific perspective, it is still not certain if Omicron causes milder disease, even though anecdotal evidence suggests so. The UKHSA said it has no data yet for infection severity as well as for vaccine efficacy against severe disease.
Scientists and pharma companies, however, are optimistic that vaccines, including regular dosing schedules, will still offer robust protection from severe disease and death because of how they stimulate the adaptive immunity. According to a statement by Pfizer on December 8, 80% of epitopes (biological features of the virus) in the spike protein recognized by CD8+ T cells (a type of immune cells) are not affected by the mutations in the Omicron variant.
Both indications may or may not be confirmed in the future, a fact that many countries appear to have recognised in speeding up their booster campaigns.
All things considered, the most hopeful of signs regarding Omicron may be red herrings that need to be avoided from a policy and public messaging perspective. The variant, as far as science knows at present, poses a significant, if not a substantial, threat.