A third wave of COVID-19 may be confined to certain states

Scientists are modelling a potential third wave of COVID-19 infections in India, which by many accounts, will not be as devastating as the second wave that peaked in May 2021.

Epidemiologists are studying local breakouts of infection in particular states of the country and trying to figure out whether they may signal the advent of a third wave. Efforts are directed at estimating the scale of a potential wave based on the infection rate trajectory.

There is a consensus that a third wave would be a more localized version than the second. “In the first and second waves, reported numbers reflected the national trend. But, in a third wave we would look at state-level granularity,” says Samiran Panda, chief of epidemiology and infectious diseases at the Indian Council of Medical Research (ICMR).

Given that more than 80% of infections were now confined to about 10 states, says Panda, a third wave in some states should not be inferred as a national phenomenon. “We need to analyse state-level data with more accuracy.”

Small spikes in parts of Kerala and Maharashtra cannot be seen to indicate an impending third wave, according to Tarun Bhatnagar, senior scientist at the ICMR-National Institute of Epidemiology in Chennai.

Local numbers

“In Maharashtra numbers have hit a plateau, and in Kerala, growing numbers might signal a third wave,” explains Gautam Menon, mathematical modeller and professor of physics and biology at Ashoka University in Sonipat, near Delhi.

Menon says it is reasonable to infer that the infection has already hit a large section of the susceptible population during the first and second waves.

The All India Institute of Medical Sciences and World Health Organization (WHO) reported high sero-positivity in a recent survey, suggesting 67% of India’s adult population was already exposed to the virus.

The high numbers in Kerala can be explained in the context of exposure to infection. “Serological studies for Kerala indicate that a relatively smaller fraction of the population may have sustained a prior infection compared to the rest of India. So, there may still be a reservoir of susceptible people to be infected there,” says Menon.

Barring the northeast states of India, cases are reducing consistently, accompanied by low test positivity rates. District-level monitoring of the trend of new cases and test positivity over a period of at least two weeks, can be a good barometer of a sustained rise or fall in cases and potential emergence of the third wave, Bhatnagar suggests.

Scientists reiterate the need to prioritise the tracking of positivity and vaccination rates, Mandal says.

“It is likely we will keep seeing outbreaks with differing local contributory factors and trajectories, such as what we are seeing currently in the northeast, in Kerala and in Maharashtra”, says Satyajit Rath, immunologist at Indian Institute of Science Education and Research in Pune.

Driving transmission

Scientists say a third wave would be driven by three factors: highly infectious new variants, free movement and crowding, and large numbers of unvaccinated people.

Pandemic fatigue among people and governments, emergence of more transmissible variants and the uneven pace of vaccination, help explain why COVID-19 infection has been more widespread this year compared to 2020, says Rath.

The WHO chief, Tedros Adhanom Ghebreyesus, has warned that the COVID-19 pandemic is now in the early stage of the third wave. As states prepare for a third wave, the Indian government too has said the next two to three months are crucial.

The worry stems from the fact that vaccination rates remain too low, and COVID-19 protocols in public are barely adhered to.

Brian Wahl, epidemiologist at Johns Hopkins Bloomberg School of Public Health says, “Most models for COVID-19 that look beyond two or so weeks rely heavily on assumptions of vaccination rates and levels of physical and social distancing.”

Wahl says some of the models that predict a third wave have “assumed current vaccination rates and non-pharmaceutical interventions like physical distancing and mask wearing.”

K Srinath Reddy, president of the Public Health Foundation of India says a third wave is expected anywhere between August and October. “We can limit it to a ripple rather than a tidal wave. If we are lax, we will suffer a severe surge.”

While the number of people susceptible to the virus will be fewer than those at the beginning of the second wave, many are still vulnerable. This will play a role if the “third wave comes in August. By October, many more will be vaccinated,” he says.

Vaccination is key to influencing the severity of a wave.

"If majority are not yet vaccinated then there is a high probability that the infection rate will go up,” says Polly Roy, professor of virology at the London School of Hygiene and Tropical Medicine.

How severe will the next wave be?

A third wave of COVID-19 in India is unlikely to be as severe as the second wave given the extent of spread of the virus, according to an ICMR modelling study, which reviewed data with assumptions to see the impact of various levels of waning of existing immunity. The modellers examined four factors – waning immunity without any change in the virus, emergence of a new virus variant capable of escaping pre-existing immunity, emergence of a more transmissible variant without loss of immunity to previously circulating strains and fresh opportunities for transmission afforded by relaxation of local restrictive measures (lockdowns).

Immune-mediated mechanisms — waning immunity or viral evolution — are unlikely to drive a severe third wave, unless such mechanisms lead to a complete loss of protection among those previously exposed, the study notes.

Likewise, a new, more transmissible variant would have to exceed a high threshold (R0 >4.5) to cause a third wave on its own, it suggests.

Bhatnagar, however, says that genetic sequencing must be used at a large scale to examine the spectrum of variants.

Mandal and colleagues have also recommended measures to take the vaccination drive closer to the people at the community level. They suggest creating satellite vaccination centres near rural hamlets and urban resident welfare associations, converting community halls and using large parking spaces for drive-in vaccination, and using mobile vaccination facilities to cover populations who cannot easily access centres.