Administering 871 million doses of Covid vaccines between March 1—when India opened up the vaccination drive to its general public—and September 28 is no mean feat. Given the country’s size and population, not only did officials and vaccinators have an enormous target to chase, but they also encountered infrastructure challenges, difficult and remote terrain, cultural sensitivities and a great deal of misinformation among people, leading to vaccine hesitancy. The dedicated and tireless efforts of thousands of healthcare workers employed under the national vaccination programme helped beat the odds and gave us some heartening success stories.

Take, for instance, the case of 92-year-old Madhavi Pillai from Kerala’s Palakkad district. A widow who lives under the care of two full-time house helps, Pillai had little hope of making it to the nearest vaccination centre for the jab. Help came by way of a local anganwadi worker, who personally accompanied Pillai to the centre for the inoculation. In Himachal Pradesh, which has completed first dose vaccination for its entire eligible population, vaccinators trekked on foot through 20 km of mountainous territory to reach the remote village of Baloth, in Chamba district, and set up a vaccination camp. They set up another camp in the middle of a wildlife sanctuary to cater to a bedridden patient from Hillotwan.

“What we have achieved is tremendous. The pace of vaccination is only going up; this is particularly notable given the sheer scale of covering such a large and geographically spread out population,” says Dr V.K. Paul, chairman of the national taskforce for Covid. “About two-thirds of the adult population has been given one dose of the vaccine; almost a quarter of the adult population has received both doses.”

On September 17, India administered a record 25 million doses of Covid vaccines in a day. So far, six states/ Union territories have given the first dose to their eligible population—Lakshadweep, Chandigarh, Goa, Himachal Pradesh, Andaman & Nicobar Islands and Sikkim. Four others—Dadra & Nagar Haveli, Kerala, Ladakh and Uttarakhand—have achieved over 90 per cent coverage for the first dose. Supply of doses, which had slowed down the vaccination drive in the initial months, has also improved. The Centre has made available 835 million doses; another 11 million are on their way. It has been a mammoth effort fraught with unpredictable problems, including the public mindset. “One of the challenges has been to get people to overcome the fear of vaccine and come for the first dose. The other has been to keep them motivated so that they return for the second dose,” says Dr Randeep Guleria, director, AIIMS, New Delhi.

Too early to celebrate

But health experts aren’t sure if the success of the ongoing Covid vaccination programme means the pandemic will be behind us soon. They say there is still not enough data to conclude that the worst is over. “There are a lot of variables with Covid. All the measures we take are based on research and science. We all have to continue wearing masks and practise Covid-appropriate behaviour for at least the next one year,” says Dr Paul.

Dr Om Shrivastava, an infectious diseases specialist and member of Maharashtra’s Covid taskforce, adds that it is too early to predict an end date for the pandemic. “We don’t know for sure how the Covid virus is going to behave in the coming future. What we thought [would happen] a few months ago is different from [how things are] today. With each passing day, we are acquiring new data,” he says.

Still, the current rates of infection and hospitalisation are hopeful signs that give the country reason to cheer. India has reported less than 50,000 new cases daily for over three months in a row, with only 26,041 new cases added on September 27. The national average of weekly test positivity rates has been less than 3 per cent for 94 days—well under the WHO (World Health Organization) benchmark of under 5 per cent. Hospitals in major cities are seeing way fewer Covid patients than in April, when the Delta variant had unleashed a deadly second wave in the country (see Is Covid Becoming Endemic in India?).

As on September 27, only 1 per cent of the total Covid beds, 1.9 per cent of oxygen beds, 2 per cent of Covid ICU beds and 3 per cent of ventilators for Covid patients were occupied in Delhi, as per state government data. In Kerala, which has the highest number of active cases, only 4 per cent of Covid patients in hospitals had critical symptoms. Yet, doctors warn against complacency. “The number of cases might have fallen but one cannot underestimate Covid and its infectivity,” says Dr Ankita Baidya, a consultant on infectious diseases at Manipal Hospitals in New Delhi.

While most states have witnessed a significant drop in cases and positivity rates since the peak of the second wave in May, islands of worry remain. Kerala, for example, had a positivity rate of 15 per cent and 157,204 active cases as on September 28. Mizoram saw a 25 per cent rise in cases in the week ending September 24 compared to the previous seven days. In Maharashtra, there has been a 59 per cent spike in weekly case growth during the same period. Delta is the dominant variant in both states. But a fresh wave of infections is inevitable should a new strain that evades our immune response emerge. Experts emphasise that allowing the virus to transmit gives it a chance to mutate.

One of the factors behind the widespread public complacency is the perception that we may have attained ‘herd immunity’. A July survey by ICMR (Indian Council of Medical Research) in 70 districts shows that close to two-third of the population in Madhya Pradesh, Rajasthan, Bihar, Gujarat, Chhattisgarh, Uttarakhand, Uttar Pradesh and Andhra Pradesh has developed Covid antibodies. The notion of immunity against Covid has prompted Delhi-based fashion entrepreneur Gauhar Kaur, 34, to plan a Diwali party this year. “Delhi has only a few hundred cases. If most of us are immune to Covid, then why live in fear?” she reasons.

Experts are more cautiously hopeful. While seroprevalence studies help understand Covid’s spread and behaviour, they are by no means a certain indicator of herd immunity. “Often people do an antibody test and think they are safe, but what is important is the type of antibody and how long it has been in your system,” says Dr Shrivastava. “For Covid immunity, the body needs to have had neutralising antibodies for at least two to three months. An antibody count alone cannot tell if you have functionally relevant antibodies needed for protection from Covid.” Dr Baidya adds that public behaviour based on information on the internet will only help the virus replicate. “Infection levels are down, but the virus is still circulating, including new strains of it. We also don’t know how long the vaccines will keep us safe, so caution should be the order of the day,” she says.

How long will vaccine protection last?

A study on 614 fully vaccinated health workers at the ICMR’s Regional Medical Research Centre in Bhubaneswar showed a significant drop in Covid antibodies within four months of taking the second dose. “But this does not mean the individual is not fully protected. T cells and B cells are also factors that help in creating a memory to fight the virus,” says Dr Sanghamitra Pati, co-author of the study published in September. It is critical to understand that antibodies are only a part of our immune response, not the entirety of it.

White blood cells are the immune system’s army against invaders. In particular, the body needs two kinds of white blood cells—B cells and T cells. These develop in the bone marrow and either stay there to grow into B cells or go to the thymus gland to grow into T cells. B cells find target pathogens, such as viruses, and are then triggered to make antibodies. Antibodies lock onto the viruses, but cannot destroy them without help. It is the T cells that destroy the pathogen tagged by antibodies. Antibodies remain in the bloodstream for varying periods, in case the same germ attacks the body again. This is how vaccines prevent diseases—they introduce the body to the virus in a way that won’t make them sick with the disease but will help the antibodies recognise the germ.

While studies have shown that antibody levels developed with Covid vaccination can drop, there is little data on the role of T cell memory. Lessons from the SARS (Severe Acute Respiratory Syndrome) pandemic in 2003, which were published in the journal Nature in 2020, indicated that T cell memory remained strong even after 17 years among many individuals who had been infected. This suggests that T cell responses can be long-lasting. However, T cell tests are rarer in the market than antibody tests and far more technical to conduct.

The ICMR is researching various immune responses against Covid-19 to understand the role and timeline of antibody and T cell protection. The studies are expected to shed light on how long vaccine-induced immunity lasts and what key factors determine it. “There is some protective immunity as well that can act against severe disease. We have observed that even the Delta variant is not fatal after two doses of the vaccine,” says noted virologist Dr T. Jacob John.

Take Covishield, of which 764 million doses have been administered in India. A study on 1.6 million healthcare and frontline workers in the armed forces suggested that Covishield reduced the possibility of infections by 93 per cent and completely protected individuals against fatalities. But another study, by the ICMR, showed the absence of antibodies after the first dose in 58 per cent of Covishield recipients and in 16 per cent who had taken both the shots. This suggests that even with reduced or no antibodies, vaccines are giving protection against infection and severe Covid disease (see Double-dose Vaccination Holds the Key).

In the absence of more robust data on the role of antibodies and the levels needed to protect against Covid, Indian experts rule out a booster vaccine dose. Booster doses, they feel, should at best be limited to immunocompromised individuals. In the US, the Food and Drug Administration (FDA) is considering a booster for everyone above the age of 16. The WHO, however, has called for a temporary halt on booster shots, citing the huge vaccination gap between wealthy and poor nations.

Dr Paul says booster shots are still a work in progress and India’s priority is to inoculate the entire population with two jabs. “Booster shots are not required currently. What type of booster shot is required, and when, will be clear as more data emerges,” says Dr Guleria. The message for the time being is to stick to masking up in public, whether or not one is vaccinated. “You will shed the virus even if you are vaccinated or recovering from Covid. To think you are safe [post-vaccination] and drop your guard could be a fatal mistake,” says Dr Guleria.

The endemic turn

An epidemic is a disease that affects a large number of people within a community, population or region. A pandemic , such as Covid-19, is an epidemic that is spread over multiple countries or continents, such as Covid-19. An endemic disease or outbreak is one that has a continuing but manageable presence in a limited region. Any disease in an endemic stage can return to an epidemic stage where infection rates are high and unpredictable. For example, dengue or influenza outbreaks happen at regular intervals in India and then recede. If their numbers were consistently and enormously high all year round, they would be an epidemic. If we project the current numbers, Covid may appear to be on its way to becoming endemic in India. Our test positivity rates, number of daily infections and R-value (average number of secondary infections produced by an infected person) have remained low and steady for over three months now.

According to the Institute of Mathematical Sciences, Chennai, the R-value, or reproductive number, for Covid-19 in India dropped from 1.17 at the end of August to 0.92 by the middle of September. The R-values of Kerala and Maharashtra, states with by far the highest number of active cases, are also below 1. Clearly, the virus is infecting small regions or populations in a consistent manner, with some weekly variations. “We aren’t going to eliminate Covid; it will become endemic eventually,” says virologist Dr Gagandeep Kang of Christian Medical College, Vellore. She adds that a national third wave could be likely if people do not observe Covid protocols during the forthcoming festival season, though it will probably not be as severe as the second wave.

Experts remain apprehensive of a lethal wave triggered by a new virus variant that escapes all previous immunity. WHO has classified two variants of interest that are yet to reach Indian shores—Mu and C.1.2 (see Mutant Watch). The Mu variant, first identified in Colombia this January, has the potential to evade antibodies, says WHO. While its global prevalence has shrunk to below 0.1 per cent, it continues to spread in Colombia (39 per cent of total cases) and Ecuador (13 per cent). The C.1.2 variant, detected in South Africa in May, is of greater concern because it has mutated the most among all Covid variants. Some 130 cases have been found worldwide.

“The C.1.2 variant has a substantially higher number of changes in its genetic make-up than any previous strain, which could make it more transmissible. It may impair the working of vaccines and change the nature of symptoms,” says Dr Baidya. “Data on these factors will emerge with time and more studies.” C.1.2 evolved from C.1, one of the coronavirus lineages that dominated the first wave in South Africa in May 2020. Researchers at South Africa’s National Institute for Communicable Diseases have been studying the C.1.2 strain and say it has undergone the maximum number of mutations from the original Wuhan strain. The rate at which infections from this strain are rising compares with those of the Beta and Delta variants in South Africa during the early days of their spread.

The Delta variant remains the dominant strain in India at present. However, its sub-lineages, which have gone from four a couple of months ago to 13, are adding cases. AY.4, a sub-lineage first spotted in the UK, was found in 1 per cent of the samples tested from Maharashtra in April. Its proportion increased to 2 per cent of the samples tested in July and 44 per cent in August. It’s dominant in Karnataka as well, with 41.1 per cent of the samples in September testing positive for AY.4—more than Delta (40 per cent) itself. AY.12, a sub-lineage first found in Israel where it caused a wave of infections despite 60 per cent of the country’s population being fully vaccinated, was detected in 10 per cent of the samples from Delhi tested in September. “A large segment of the Indian population is still unexposed to Covid. The Delta variant alone can cause regional spikes,” warns N.K. Arora, a member of the national taskforce on Covid-19.

Covid is perhaps unlike any virus the world has seen in living memory. The Swine Flu pandemic claimed 284,000 lives globally in its first year (2009); Covid claimed 2 million people. Covid is significantly more contagious than Swine Flu and mutations are making it both more infectious and less susceptible to human immune responses. With less than a year of vaccination data, researchers say it’s too soon to conclude whether vaccines and previous exposure to the virus will protect individuals from the current strains of Covid. What is certain, though, is that adherence to masking/ social distancing and strategic lockdowns can keep the numbers down. “How devastating a potential third wave can be depends on public behaviour,” says Dr Guleria.

The long festive season, beginning with Navratras in early October, will be a vulnerable period, but if India can contain cases at the current levels—thereby reducing the threat of fresh mutations of the virus—Covid will gradually turn endemic. The virus is here to stay, and one has to learn to live with it. But with vaccination and due precautions, it probably won’t cause the scale of sickness, death and grief that the country witnessed earlier this summer. n