How fast does the Omicron variant intrinsically spread, and does it have a significantly altered transmission dynamics?

The answers to these questions, still being worked out by scientists, will help determine the steps and degree of compliance required to bend the Omicron wave.

We know that the variant spreads rapidly and there are at least three factors that are at play: infections now have a shorter incubation period, infected people have high viral load in upper air passages early on, and even brief exposure may trigger infection.

These insights have been gleaned from epidemiological tracking and scientific studies. For instance, the UK’s travel advisory issued in early December cited assessments saying the incubation period – the time between infection and symptoms, which is correlated with contagiousness – has likely dropped from a week to three days or fewer.

Lab studies in the recent month have shown the virus multiplies more intensely in the bronchus – the passage leading to the lungs – but less efficiently in the lungs. A University of Hong Kong research found the replication in the bronchus may be 70 times more than the Delta variant.

The third factor is perhaps best illustrated in a contact-tracing investigation in Hong Kong. Authorities there found that an Omicron-infected person passed on the disease to a person in the opposite room in a quarantine hotel despite them having never interacted — corroborated by CCTV evidence.

Together, they suggest Omicron’s inherent transmissibility is high. Inherent transmissibility is denoted as the basic reproduction number, or R-nought, or R0 — an estimate of the number of secondary infections each infected person will cause on average.

Delta’s R0 is estimated to be 5, and that of the ancestral variant from Wuhan was estimated to be between 2 and 3.

Omicron’s R0, according to estimates by the London School of Hygiene and Tropical Medicine experts, could be as high as 10.

To bring an epidemic under control, the effective R number must be brought down to under 1, which means on average, infected people do not pass it onwards.

What will it take to get Omicron’s R to under 1?

A team of researchers led by scientists from Germany’s Max Planck Institute in a recently released study have estimated how different measures – vaccination, face covering, social distancing and ventilation – can bring down the effective R number of a Sars-CoV-2 variant, and how many people need to follow it.

For Delta, they found that if a region has 70% vaccination coverage, and if three out of 10 people are disciplined on social distancing, using masks and ventilation, it will be enough to contain an outbreak by bringing the R number 1. In the case of schools where children are mostly without doses, the effect of lower vaccination rate can be overcome by carrying out 2-3 tests per week, they said.

“If the Omicron variant were to reach R0 = 8, it could still be contained with the synergetic measures outlined above,” they said in their report.

But there’s a problem if Omicron has an inherent transmissibility like measles, with an R0 of 12 to 18. “In these cases, higher compliances and testing rates or additional measures like general contact reductions would be required,” they added.

In other words, more people — with almost near-complete compliance — will need to mask up, maintain distancing, be in well-ventilated spaces and, most of all, take doses of vaccines with high efficacy against disease and transmission.

Two years after the pandemic, this might seem like a natural conclusion. But Omicron has eroded vaccine efficacy to staggering levels, making protection from symptomatic infection – and thus transmission – below the standard bar of 50% in the case of all vaccines, without boosting.

In India, 65% of the adult population has been fully vaccinated and none of them are yet to receive booster doses.

And then there is compliance in masking and social distancing, or a stark lack thereof in the country..

The variant is up to 70% less likely to lead to hospitalisation. The number is not 100%, which means even a minute risk of hospitalisation is a significant threat for a populous country like India. As the researchers in Germany show, it is now more crucial than ever for the country to adhere to protective measures and boost its vaccination coverage.