A new variant of the Covid-19 virus, named Omicron, has taken the world by storm ever since it was reported by South Africa on November 24, with the earliest sample dating back to November 9. Since then, it has been detected in 77 countries, showing local transmission in many and spreading rapidly. New modelling studies suggest 25,000 to 75,000 deaths in England by the end of April 2022. This has raised concern, especially since England has so far given two doses to about 70 per cent and a booster dose to about 35 per cent of its population.
What do we know about the Omicron variant? It has by far the highest numbers of mutations of any other variant — 50 in all when compared to the original Wuhan virus. Of these, 32 make changes to the spike protein that covers the virus surface and 10 are in a region of this protein that promotes virus entry into our cells. Several of these mutations are found in other variants as well, but never came together in a single variant earlier. How do these changes alter the phenotype (behaviour) of the virus?
Data from South Africa and several European countries show a doubling rate of two to three days. A UK report shows its transmission in a household setting to be three-fold higher than Delta. Such rates can lead to an exponential rise in cases. But the good news is we know how to reduce spread with mitigation measures such as masks, ventilation, avoiding crowds, etc. Another piece of good news is that wherever Omicron is gathering steam, the proportion of people with severe disease is lower than expected. A large study by Discovery Health, South Africa’s largest health insurer, released on December 14, showed the risk of hospitalisation among adults who contracted Covid-19 to be 29 per cent lower.
Researchers from the University of Hong Kong reported on December 15 that Omicron infects and multiplies 70 times faster than the Delta variant in the human airway, but infection in the lung is significantly lower. This could explain why Omicron transmits faster between humans but shows reduced disease severity.
Several laboratory studies have shown sera from people who had prior infection or vaccination or a combination to poorly neutralise the Omicron variant. First readouts on the effectiveness of the Pfizer vaccine show that over five months, it drops to 60 per cent against Delta and about 34 per cent against Omicron. A booster dose makes the vaccine 95 per cent effective against Delta and about 75 per cent against Omicron. This translates to about five times more breakthrough infections by Omicron compared to Delta.
Where does India stand? By July 2021, the 4th National Serosurvey estimated 67.6 per cent of Indians to have antibodies. Considering that the vaccinated fraction was very low by then, much of it came from infection. Despite an impressive delivery of 1.3 billion doses, only 38 per cent of Indians have received two doses and 59 per cent have received one dose. Global data shows that people with prior infection with other variants have minimal capacity to neutralise Omicron. This together with past experience and demography suggests that there may be rapid expansion of symptomatic infections in India over the coming weeks. While hospitalisations may remain lower than in the earlier waves, even a small fraction of a very large number is a large number. It is, therefore, prudent to keep hospital capacity ready and ensure adequate stocks of medicines, oxygen, etc.
India must also increase the pace of its vaccination to cover as many people with two doses as possible. Reducing the gap between two doses of Covishield from 16 to 12 weeks will speed this up. Though it is unlikely to stop symptomatic infection, a combination of prior infection and vaccination in a large fraction of adults will ensure low rates of severe disease, hospitalisation and mortality. Simultaneously, India should urgently formulate clear policies on vaccine boosters and vaccinating children. What vaccines can be used, how many doses would be needed, when should these be given and who should be prioritised?
About 90 per cent of doses given in India are of Covishield, which would not work well as a booster dose in people who have already received two doses of it. What are the other options? Covaxin can be used as a booster for people vaccinated with two doses of Covishield and vice versa. The DNA vaccine ZyCoV-D can also be used. There are two protein vaccines available to India that will work well as boosters. Covovax manufactured by the Serum Institute of India for Novavax (USA) has completed phase 3 trials, is approved in Indonesia and SII has exported 50 million doses. Corbevax-E is manufactured by Hyderabad-based Biologicals E in partnership with Baylor College of Medicine and Dynavax Technologies (USA). Both vaccines await emergency-use approval in India.
A policy for boosters, like everything else, should be based on evidence, not emotion. Global data shows two doses are essential for protection from disease and a booster protects further from symptomatic infection. While we await local data, let us not delay preparing for boosters and vaccinating children.
Indians are not insulated from the world. This is one lesson we have learned painfully over the past year.
This column first appeared in the print edition on December 17, 2021 under the title ‘Preparing for Omicron’. The writer is a virologist and fellow, OCIS and Green Templeton College, University of Oxford, UK. He is also a Visiting Professor, Ashoka University, India