The Omicron sub-variant driving the surge
Source: By Anonna Dutt: The Indian Express
The current surge in Covid-19 infections in China is believed to be driven by the BF.7 sub-variant of Omicron that is circulating in that country. This isn’t the first time that BF.7 has made news — in October, it started to replace the variants that were then dominant in the United States and several European countries.
What do we know about BF.7?
When viruses mutate, they create lineages and sub-lineages — like the main trunk of the SARS-CoV-2 tree sprouting branches and sub-branches. The BF.7 is the same as BA.5.2.1.7, which is a sub-lineage of the Omicron sub-lineage BA.5.
A study published in ‘Cell Host and Microbe’ journal earlier this month reported that the BF.7 sub-variant has a 4.4-fold higher neutralisation resistance than the original D614G variant — meaning that in a lab setting, antibodies from a vaccinated or infected individual were less likely to destroy BF.7 than the original Wuhan virus that spread worldwide in 2020.
But BF.7 is not the most resilient sub-variant — the same study reported a more than 10-fold higher neutralisation resistance in another Omicron sub-variant called BQ.1. A higher neutralisation resistance means there is a higher likelihood of the variant spreading in a population and replacing other variants.
BF.7 accounted for more than 5% of US cases and 7.26% of UK cases in October. Scientists in the West were watching the variant closely; however, there was no dramatic increase in the number of cases or hospitalisations in these countries.
Is BF.7 circulating in India as well?
The January 2022 wave in India was driven by the BA.1 and BA.2 sub-variants of Omicron. The sub-variants BA.4 and BA.5 that followed were never as prevalent in India as they were in European countries; thus, India saw very few cases of BF.7 (which is an offshoot of BA.5).
As per data from India’s national SARS-CoV-2 genome sequencing network, BA.5 lineages accounted for only 2.5% of cases in November. At present, a recombinant variant XBB is the most common variant in India, accounting for 65.6% of all cases in November.
So, what was different in China?
Experts believe that it is not the higher transmissibility or immune evasiveness of the BF.7 variant that led to the increase in cases in China, rather an immune-naïve population drove the numbers.
Dr Anurag Agarwal, former head of India’s Covid-19 genome sequencing consortium INSACOG, said, “China is now experiencing the typical Omicron surge that other countries have already witnessed, and just like the one Hong Kong saw when it relaxed its restrictions.”
“For us, the Omicron wave looked milder because the population was protected with previous infection and vaccination. Plus, we have already paid the price, so to say, during the Delta wave (of April-May 2021). People died but those who survived had better immunity. Other than that, Omicron has mainly been killing its elderly victims and we (India) do have a younger population,” Dr Agarwal said.
This is the reason even highly transmissible variants haven’t led to a deluge of cases, with most people recovering after a bout of fever, cough, and sore throat.
Dr Agarwal said that the only countries that did not pay much of this “price” were those that remained completely closed until they were able to vaccinate the entire population and then open up — Australia, New Zealand, and Singapore.
He added that case numbers were no longer that important because the rise in infections is largely not accompanied by an increase in the number of severe cases that need hospitalisation or lead to deaths.
“With Omicron continuing to mutate to escape the immune pressures, we have been seeing increases in cases in many countries from time to time.”
But isn’t a large chunk of China’s population vaccinated?
China indeed has a high vaccination rate — 235.5 doses per 100 population as per the WHO dashboard. However, China was among the earliest countries in the world to develop and administer vaccines to its population, and its vaccines were developed against the original variant of the coronavirus.
The virus has mutated many times over since the beginning of 2020 — and the Omicron variants are known to evade the immune response from most vaccines currently in use.
(Indeed, India’s Omicron wave infected a very large number of people who were already double vaccinated.) This is the reason many companies have come up with bivalent vaccines to provide better protection.
“Until Omicron, vaccines could control the spread of the infection. After Omicron, the vaccines aren’t really able to stop transmission, but they do prevent deaths,” Dr Agarwal said.
He also pointed out that mRNA vaccines (like the ones developed by Pfizer and Moderna) have proved to be more successful than the ‘dead virus’ vaccines like the ones used in China. “There is a debate about whether certain vaccines are better than the others. And, Hong Kong presents clear evidence that people who received the mRNA vaccines fared better than those who received the killed virus vaccine,” Dr Agarwal said.
Is there a danger of another bad global wave of the pandemic?
Dr Ekta Gupta, professor of virology at the Institute of Liver and Biliary Sciences that is linked to INSACOG, says although the possibility of a new variant emerging because of the high transmission in China cannot be ruled out completely, it is unlikely.
“The mutations in the spike protein have slowed down, there hasn’t been a massive change in around a year. This is why we haven’t seen any new variant emerge, just sub-lineages. If you see, the distance between the spike protein in the original D614G variant and Delta, or even between Delta and Omicron, was much more than what we are seeing now,” she said.
Dr Gupta, however, cautioned against doing away with all precautions. “SARS-CoV-2 is now a human virus and it is here to stay. There could be an increase in the number of Covid-19 cases in the winters, when we usually see an increase in all respiratory infections.”
