Several parts of the world have been reporting an increase in fresh cases of Covid-19, but in India, experts believe that unless a deadlier variant of the virus emerges, the country is unlikely to witness another wave of infections.

The widespread exposure of the Indian population to the virus, especially during the deadly second wave in the summer of 2021, followed by expansive vaccination coverage, has possibly provided it a higher degree of immunity when compared to other countries with high vaccination but low past exposure, say epidemiologists.

On March 18, India reported 2,528 new Covid-19 cases, a marked decrease from the nearly 27,000 fresh infections being recorded until mid-February as the third wave fuelled by the infectious Omicron variant was subsiding. More than 80% of the adult population has received both doses of Covid-19 vaccines.

While India’s daily caseload has been steadily declining, several other countries are reporting an increase in cases. China is witnessing a record surge in infections, the highest since the pandemic first broke out in Wuhan city in December 2019.

Cases in Mainland climbed to a high of 5,280 on Tuesday, according to AFP. Such numbers were noted in early 2020 when the country recorded 3,000 to 5,000 cases daily.

China, which follows a zero-Covid policy, has imposed stringent restrictions in multiple parts of the country. The surge in China is driven by both the Delta and Omicron variants. A sub-lineage of Omicron, BA.2, also being referred to as stealth Omicron, is spreading fast in the Chinese population.

The Robert Koch Institute, which is monitoring the pandemic situation in Germany, said the country reported 2,94,931 fresh cases on March 17.

Other European nations, such as Finland, Switzerland, Netherlands, Italy and the United Kingdom, have also reported high numbers where the sub-lineage of Omicron BA.2 is spreading. Nearly 65% of Europe’s population has been fully vaccinated, according to Our World in Data.

A woman gets tested for Covid-19 at a mobile nucleic acid testing site in Beijing, China, on Friday. Credit: Carlos Garcia Rawlins/Reuters

South Korea, which won high praise for keeping infection numbers low, recorded more than six lakh cases on March 17, the highest since January 2020. At least 87% of South Korea’s population has been fully vaccinated, with boosters rolled out for the vulnerable as well.

On March 17, Tedros Adhanom Ghebreyesus, the Director General of the World Health Organization, said that cases had started increasing globally after several weeks of decline.

The increase in cases in countries which have high vaccination and booster dose rates, has sparked concern. In India, too, the prediction of a four-month-long fourth wave beginning late in June caused alarm.

The study, by the Mathematics and Statistics department of the Indian Institute of Technology, Kanpur, was published MedRxiv. It has not yet been peer reviewed.

The findings, which are based on mathematical modelling called Sutra, do not predict a strain on the health infrastructure in the possible event of a fourth wave. Epidemiologists, however, believe the declining trend in Covid-19 cases will continue in India.

High immunity in Indian population

Virologist Dr T Jacob John said the current surge in several other countries is being driven by the highly infectious Omicron variant.

India witnessed the third wave of the pandemic, fuelled by the Omicron variant, between January and February due to Omicron, when daily fresh cases peaked at 3.47 lakh on January 21.

According to data shared by the Union Ministry of Health and Family Welfare on Thursday, India recorded 77.42 lakh Covid-19 cases during the third wave that spanned over 42 days. The third wave ended by February 14, according to the ministry.

“It’s like swimming in a river,” said John. “We in India have crossed that river, some other countries are still swimming in it.” According to the virologist, the spread of Omicron was delayed in Europe, China and Korea. “The rise we see now in those countries is due to that,” said John. He also said high vaccination rates have helped keep the Omicron wave comparatively mild in India.

At the onset of the third wave, India had covered nearly 90.8% of its adult population with a single dose of the vaccine while 65.4% had received both doses. During the third wave, 27,118 deaths were recorded, as compared to 2.52 lakh deaths during the second wave in April and May last year. Single-dose vaccine coverage in the adult population when the second wave began was 10%.

Public health expert Dr Chandrakant Lahariya said countries that first vaccinated a large section of the population, which then got exposed to the virus, are seeing more infections with severe symptoms than countries where the population was first naturally exposed to the infection and then vaccinated.

“The combination of immunity developed due to natural exposure and immunity generated by vaccination is working strongly against the virus,” Lahariya said.

He said that India also experienced a brutal wave led by the Delta variant during summer last year which also gave the population immunity against severe infection. “The Covid-19 pandemic is over for India,” he said.

Lahariya said that in the case of China, the country never recorded a natural infection the way India did. “Majority of its population is still susceptible,” he said. Both vaccines manufactured by China, CoronaVac and Sinopharm, have the lowest efficacy compared to all other vaccines, according to Lahariya.

He said South Korea, too, had an early wave, which was followed by a long span without a significant spurt in cases, making its population more susceptible.

At-risk, elderly citizens

The demographics of a country also play a role in infection susceptibility. Dr Gagandeep Kang, a microbiologist at Christian Medical College, Vellore, said European countries have a higher share of elderly citizens and therefore continue to witness more infections and hospitalisations than India.

According to Kang, a person who receives both shots of the Covid-19 vaccine after recovering from an infection has stronger protection compared to someone who has received two doses and a booster shot.

“Since a large section of the population has been exposed to the virus and got vaccinated, it is safe to assume people have stronger protection,” she said.

Kang said unless a new variant emerges, more severe than Delta and more transmissible than Omicron, there should be no worry of another wave in the country.