India’s third wave of COVID-19 may be in pockets
doi:10.1038/nindia.2021.102 Published online 20 July 2021
Scientists are racing to prepare for and mathematically model the possibility of a third wave of COVID-19 infections in India, which by most accounts may not be as devastating as the second wave that peaked in May 2021.
Epidemiologists are keenly studying local breakout of infection in some states of the country and trying to figure if it may signal the advent of a third wave. Efforts are on to estimate the scale of an impending wave, defined by increased number of infections across the country.
On this alone, there is a meeting of views. The third wave is likely to be more localised, if and whenever it starts.
“In the first and second waves, reported numbers were a reflection of the national trend. But in the third wave we have to look at state-level granularity,” says Samiran Panda, head and chief of epidemiology and infectious diseases at the Indian Council of Medical Research (ICMR).
Given that over 80% of infections were now confined to about 10 states, says Panda, a third wave in some states should not be inferred as a country-wide wave. "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 at this point of time,” agrees Tarun Bhatnagar, senior scientist at the ICMR-National Institute of Epidemiology in Chennai.
Pointing to the “blips in some states, of late”, the third wave, Panda says, should be assessed keeping in mind the “heterogeneity of states”.
Rising local numbers
“At the moment, what is happening in Maharashtra (numbers have hit a plateau) and Kerala (growing numbers) might signal a third wave in those states”, explains Gautam Menon, mathematical modeller and professor of physics and biology at Ashoka University in Sonepat near Delhi.
Menon says a likely inference is that the infection has already “burned through” 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 percent of adult population in India 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.
A surge in cases now would be because the population is not yet exposed to the virus either through natural symptomatic or asymptomatic infection or vaccination, says Bhatnagar.
Barring in 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 at least a two-week period can be a good barometer of a sustained rise or fall in cases and potential emergence of the third wave, suggests Bhatnagar.
Scientists reiterate the need to prioritise the tracking of positivity rate and vaccination. Mandal says, “Vaccination has to be prioritised, especially in areas with high positivity rate.”
“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.
What influences a wave?
The three things that scientists say will drive a third wave are highly infectious new variants, free movement and crowding of people and large numbers of unvaccinated people.
Pandemic fatigue among people and governments, emergence of more transmissible variants and slow uneven pace of vaccination explain why COVID-19 infection has been more widespread this year compared to 2020, says Rath.
A possible third wave can be precipitated by waning immunity among people, emergence of a more transmissible variant and relaxations by governments in lockdown curbs, Randeep Guleria, AIIMS director, was similarly quoted as saying.
WHO chief Tedros Adhanom Ghebreyes 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 tardy and COVID-19 protocols in public are barely adhered to.
Dr Brian Wahl, epidemiologist and faculty 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. “If we follow COVID-19 appropriate behaviour and prevent super-spreader events, 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 less 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.
Mathematical models have shown vaccination can help flatten the third wave, says Panda. “We should understand that the second wave has not vanished. Ramping up vaccination can reduce severity of the disease to a large extent,” he says.
Wahl echoes this. Increasing vaccination and adhering to COVID-19-appropriate behaviour can help either prevent or mitigate a third wave. “We have seen this in our models. All the more important in the context of a more transmissible Delta variant.”
India vaccinated 8.6 million on June 21, its highest number of daily inoculations against COVID-19. Numbers have been steadily declining since. Barely 6% of its population is fully vaccinated. “Focus should be on vaccinating around 10 million people per month and addressing vaccine hesitancy,” says Bhatnagar.
“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 study1.
The study 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 for immune escape — are unlikely to drive a severe third wave if acting on their own, 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 level2. 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 access vaccination centres easily.
1. Mandal, S. et al. Plausibility of a third wave of COVID-19 in India: A mathematical modelling based analysis. Ind. J. Med. Res. (2021) Doi: 10.4103/ijmr.ijmr_1627_21
2. Mandal. S. et al. Responsive and agile vaccination strategies against COVID-19 in India. Lancet Glob. Health. (2021) Doi: 10.1016/S2214-109X(21)00284-9