Mistaken Notions Of Herd Immunity Led to India’s COVID-19 2nd Wave

Why is this second wave occurring now? What more must India do, from a public health and individual perspective?

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As 2021 began, India was thought to be slowly seeing the back of COVID-19. New cases had fallen dramatically across the country since the highs of mid-September. Now, that's been reversed, more so in some parts of India. Over 80 percent of new COVID-19 cases in India's 'second wave' are from six states: Maharashtra, Punjab, Gujarat, Chhattisgarh, Karnataka and Kerala, per Ministry of Health and Family Welfare (MoHFW) data. Maharashtra, Punjab, Chhattisgarh, Tamil Nadu, Karnataka and Kerala also accounted for over 80 percent of deaths from COVID-19 on 24 March.

Maharashtra leads in the number of new cases, with 28,699 on 23 March. Mumbai alone is witnessing record numbers of new infections, surpassing its peaks in 2020. As cases surge, Mumbai and Delhi have banned public celebrations of festivals; Mumbai is conducting rapid antigen tests randomly in crowded public areas; and the suspension of international commercial passenger flights has been extended to 30 April, 2021. Meanwhile, more than 50 million people had received at least one dose of a COVID-19 vaccine by 24 March, and India's vaccination programme is expanding to include all aged 45 and above, with or without comorbidities.

Why is this second wave occurring now? What more must India do, from a public health perspective, and what must we as individuals do? To understand this, we spoke with K. Srinath Reddy, president of the Public Health Foundation of India, adjunct professor of epidemiology at Harvard T.H. Chan School of Public Health, and former head of cardiology at the All India Institute of Medical Sciences.

Edited Excerpts:

The trajectory of new COVID-19 cases, which had been moving downward since mid-September 2020, has suddenly reversed and seemingly quite late in the day. To use a light analogy, this is almost like a big surprise on day 5 of a five-day cricket test match. Why is this happening?

It's not day 5 of a test match; we are still very much in the middle of the match. In fact, we started playing this game not as a test match but as though it's a T20, and thought the game was over. That was the big mistake we made. It's very clear that by January 2021, COVID-19 cases had come down in India after the big rise up to the middle of September 2020, for several reasons. We now know that laxity set in at different levels after that.

At the individual level, COVID-19 precautions were abandoned, in terms of masks not being worn, crowding, moving around, celebrating whether in outdoor places or, particularly problematically, in enclosed places. That has been a major issue. The resumption of economic activity also brings a large number of people together for a long period of time, in offices, factories and in public transport. But even enforcement by authorities has slackened. We have seen that in the number of political meetings and rallies being organised, with elections being held at the block, local body and assembly levels. Large political and religious gatherings have been permitted.

There was also a feeling that herd immunity is already upon us. I have been cautioning against this for quite some time. Don't think of herd immunity as some Nirvana; it's not yet here and we don't know when it will arrive. Yet that feeling took hold of the political class and industrialists and then percolated, to some extent, into the public health community, with some sections propagating the idea that herd immunity is already here in India. They are also partly responsible.

There is also the challenge of mutant strains of COVID-19. With international travel now increasing, mutants that developed elsewhere are already in India. We, however, don't know the extent to which these are responsible, or not, for the rise in cases, because the genomic screening of various positive tests is not at that level.

Editor's note: While we spoke with Reddy, the Ministry of Health and Family Welfare announced that the Indian SARS-CoV-2 Consortium on Genomics (INSACOG) had detected 771 variants of concern from a total of 10,787 positive samples of COVID-19 shared by various states and union territories. INSACOG had conducted genome sequencing and analysis on samples from arriving international travelers, contacts of those positive for COVID-19 variants, and community samples. While identifying several COVID-19 variant strains and a new double mutant variant found in India, the ministry's release said these had not been detected in numbers sufficient to explain the rapid increase in COVID-19 cases in some states.

COVID-19 seems to be spreading in the southern and western regions of India, with central and eastern India relatively less affected. Many political rallies are in eastern states like West Bengal, which for the present are not seeing a surge in cases. In Maharashtra, in Mumbai city, there is a huge surge. Why is the surge confined to these places? Is there something the data are not capturing, or is there something we're missing?

It's possible that there is under-testing and undercounting of cases, but I believe it is much more the socio-economic gradient that is determining how COVID-19 is spreading, because the virus travels with the people and celebrates with the crowds. Yes, there are more elections happening elsewhere, but even states in the south and west have seen local body elections and religious festivals, so it's not as though they have not seen crowded events.

I have also maintained that COVID-19 spreads along different patterns, based on the level of economic development as well as urbanisation in a region. This is true globally, when you compare countries and regions, and it is true within India when we compare different regions. The more urbanised a state, particularly which has large, densely crowded cities, sees a lot of inter- and intrastate travel, and has a lot of industrial activity, there are greater opportunities for the virus to spread. That's why these mostly southern and western states, and some in the north like Delhi that are more urbanised, industrialised and connected are seeing more cases, whereas others which are much more rural, see few international or domestic flights and trains, and where there is less intrastate commuting, are not seeing much of spread of COVID-19. This happened last year and it's happening again now.

Why has this second wave occurred so late? In other parts of the world, the spread of the virus seems to be going downward. In the West, case numbers were rising till vaccinations took off in a big way. So is vaccination the factor that can arrest the spread of COVID-19, or is it something else? And if this second wave could happen in India, how must we prepare for a potential third wave?

I don't think just the level of COVID-19 vaccination matters, because the US and UK have also applied strict controls, despite the fact that their population that is vaccinated is fairly high. You can't depend only on vaccination; you have to make sure that the public health measures are strictly enforced. This is because vaccination takes time. Vaccinating with two doses takes about six or eight weeks for full immunity to come through. Israel is the glorious example of high levels of vaccination coupled with public health measures that have succeeded.

Further, there is not yet convincing evidence that intramuscular systemic vaccine per se is going to bring down the transmission rate substantially. That transmission from person to person can be curtailed through vaccination alone is not yet proven. Most likely it will happen, because if vaccination doesn't let a person get very sick, then that person is unlikely to discharge too many viral particles, and therefore infecting others is less of a probability. But the fact is, unless public health precautions are in place, along with fairly rapid and extensive vaccination, you're not going to get quick control.

The countries which are combining both the strategies are the ones that are really succeeding at the moment. The UK has applied many restrictions. They are fining anyone travelling outside the country. So they are limiting travel, meeting, closing down a large number of restaurant-related activities. So vaccination is only one part of it.

You raised the idea of a test match, so let me give you an example. When you're facing a huge score, then you need a good batting partnership. One person plays very strong defence and holds one end up, while the other keeps scoring briskly, to cut down the vulnerability gap. So you need to hold on to your public health precautions very strongly, at the same time you need to vaccinate faster, so that you are covering both fronts.

There was a feeling at the end of 2020 that COVID-19 had already swept through large parts of India, therefore there was high seroprevalence and some degree of herd immunity. Does this second wave suggest that there was no such seroprevalence to start with, or the virus had not swept through as much of the country as initially thought?

The Indian Council of Medical Research, in its third national survey conducted in December-January, reported a 21 percent COVID-19 seroprevalence. We do not even know what the herd immunity threshold is for COVID-19. Assuming that by February, prevalence was at 30-35 percent in India, this would still have fallen short. We got news from Brazil that 76 percent of people in Manaus tested positive for COVID-19 antibodies, yet the virus is still sweeping through there. So we know that even if prevalence is at 60 percent, it's not enough, and we are nowhere close to that in all of India. Once uncontrolled travel is permitted between places in India and within the large cities, then you're giving the virus a chance to spread. And if you're allowing international travel, mutants will also come in. So India did not attain a level of immunity that made us exempt from either the still circulating COVID-19 virus or the newly-entering mutants.

Mortality numbers are clearly lower in this second wave. But there is also concern about whether the mortality numbers are accurate, particularly when compared with the numbers from 2020. Mumbai has seen almost 25,000 excess adult deaths in 2020, compared to the average of the previous five years. States like Kerala, meanwhile, are showing fewer deaths in the pandemic year of 2020, than in previous years. What explains this? Do the mortality data give us any conclusive understanding or insight into how the COVID-19 virus is behaving?

Every time India reports low mortality figures, people jump up saying there is undercounting. It is possible, to some extent, that there will be undercounting. It's happening elsewhere too and possibly in India as well. But that does not explain the whole picture. It is easier to undercount cases because of problems with testing, but it is much more difficult to undercount deaths. And even if there is undercounting, it's still unlikely to be by a factor of five or 10; it may be by a factor of two. So we are not seeing a large number of deaths.

The question is, are we seeing less virulent forms of COVID-19 now compared to the past. There is a theoretical reason why that could happen. When the virus has nearly exhausted a large number of susceptible hosts in its first sweep, and the other susceptible persons are protecting themselves well with precautions like using masks, it is now finding few people to spread to. Therefore, it becomes more infectious in its form but less virulent, because it cannot wipe out its own existence. So then, it can start spreading much faster but causing less of a problem in terms of virulence.

The other reason why we could be seeing fewer fatalities this time around is because of the health system effect. India is much better prepared now. We know that not everybody requires a ventilator, that oxygen and home care helps. Also, because at least some people are wearing masks, then the viral load for even an infected person is going to be much less. So the severity of the disease may have altered, but our capacity to manage cases is much better, and that's why probably we are seeing less mortality. But this doesn't mean we should be careless again, because if many more people get infected, then even if the virulence remains the same or slightly less, the total number of cases getting seriously ill as a fraction of the larger case count will still be high.

Looking ahead, how should India respond at a public health level, and we at an individual level?

At the individual level, it's absolutely necessary that we must take all the required precautions, in terms of wearing masks regularly and properly outdoors, and avoiding crowded, ill-ventilated areas. Don't gather in large crowds for hours together. Avoid celebratory events, especially in indoor spaces. These are essential precautions that need to be taken. They sound so boring, because they've been repeatedly stated, but they are absolutely essential.

Then, India must increase vaccination rates. I am glad the government has said everybody above 45 years can now get vaccinated, because we know that many comorbidities are undiagnosed. A lot of people above the age of 45 with diabetes and hypertension may not be aware of this. It is important to note that in India, particularly in urban India but also in rural areas, there is a much higher prevalence of comorbidities at younger ages compared to the West. Just to give you a few statistics, take the city of Delhi and compare it with Italy. In Italy, the prevalence of hypertension in the age group of 40 to 50 years is 10.7 percent; in Delhi, it is 40 percent. In the age group of 50 to 60 years, the prevalence of hypertension is 45 percent in Delhi and 27% percent in Italy. In Delhi, the prevalence of diabetes above the age of 20 is 25.2 percent--threefold that of Italy. We know that people above the age of 40 are very vulnerable to COVID-19, so it is time to give them the vaccine without asking for a medical certificate.

When you say diabetes in people aged over 20, are you referring to above 20 in general or ages 20 to 30? Are even Indians at 20 years of age disproportionately diabetic?

Above 20, in general. I didn't want to frighten you with the statistics on pre-diabetic levels, which is about 45 percent. If you combine both, about 70 percent of people above 20 are affected, and all of them are likely to get severely ill if they are struck by the COVID-19 virus. Obviously, the rates of infection in persons aged 20 to 30 will be lower than those aged 40 to 50. So at least start vaccinations for 40- to 45-year-olds, and then cover everyone else. Tell them that they are more vulnerable because of this variety of reasons--diabetes, hypertension and abdominal obesity.

(This story was first published in India Spend and has been republished with permission)