What is ‘hybrid immunity’? Will it save us from a 4th wave of pandemic?

Hybrid immunity is behind India's low COVID-19 numbers. Genome sequencing shows that the Indian population is already exposed to the Omicron variant.

New Delhi, Dec 29: Just when Covid-19 pandemic related terms such as 'RT-PCR', 'antibodies' and 'herd immunity' were fading away from our memory, this sudden surge of cases in China has crashed them back into our consciousness at the fag end of 2022.

The resurgence has been assigned to a cocktail of Covid-19 variants which behave differently due to local epidemiology. Many are worried whether India would see a fourth COVID wave in the coming months. The government had earlier cautioned that the next 40 days will be crucial as India may see a surge in January.

However, Dr. Anurag Agrawal, director of the CSIR-Institute of Genomics and Integrative Biology (IGIB), has said that the likelihood of a fresh major wave of the pandemic in India is very low. Dr. N.K. Arora, who is closely involved in the rollout of vaccines from the onset of the pandemic, also assured that a fresh outbreak of severe Covid cases and hospitalisation is unlikely as the people of India have the advantage of 'hybrid immunity'. So, what is hybrid immunity?

According to the World Health Organisation (WHO), hybrid immunity is defined as the immune protection in individuals who have had one or more doses of a COVID-19 vaccine and experienced at least one SARS-CoV-2 infection before or after the initiation of vaccination. In simple terms, a combination of immunity gained from a natural infection as well as from vaccines.

But how well does such hybrid immunity protect us from a fourth Covid wave? According to the government records, as of now, booster dose coverage in India, which is permitted for all aged 18 years and above, stands at just 30 percent of the eligible population group. The majority of the population has taken the first two shots and others may have developed some level of natural immunity against the virus variants after being exposed to the infection.

This situation in India is different from that in March 2020, when the SARS-CoV-2 had just begun. It acquired a number of mutations which led to a number of variants and sub variants, such as Alpha, Delta and Omicron.

While hybrid immunity is behind India's low COVID-19 numbers, it must be noted that the new variants - Omicron and its sub-variants - have a higher transmissibility, as well as the ability to escape the immunity offered by vaccinations/earlier infections. Although Omicron had nearly 70 times higher infectivity rate, it did not cause much severity as compared to the Delta, which drove the second wave in India.

During the third wave, India was slightly at a better place and was not as severe as was feared. Most of the cases reported were asymptomatic or mildly symptomatic, and severity was mostly limited to the people with comorbidities. In mid-January, it was also observed through genome sequencing that the Omicron variant was found in more than 90 per cent of Covid samples tested in Delhi. This shows that our population has already got exposed to the Omicron variant.

So, now the question remains: Why is it causing havoc in China? The reason is China's 'zero-Covid' policy, which restricted people from moving out by imposing a strict lockdown in cities where even a single case was reported.

Dr. Arora said the surge in COVID cases is because they have not been exposed to the virus before, and the vaccine they got is probably less effective. However, he clarified that only one variant is not responsible for the current wave of COVID-19 in China, Japan and South Korea. There are three more variants that are a result of mutations that have taken place in the Omicron strain.

Apart from BF.7, Three variants of Omicron strain are - BN and BQ series, and SVV variant. He further said that the BF.7 variant only accounts for 15 per cent of the cases. The majority - 50 per cent - is from the BN and BQ series and SVV variant is 10-15 per cent.