- The differences between the effects of the delta and the omicron variants don’t reflect in the numbers that we’re using to track India’s COVID-19 epidemic.
- Both K. Srinath Reddy and Brian Wahl said the hospitalisation rate remains a crucial indicator today of the epidemic’s stress on the healthcare system.
- The Indian government hasn’t been sharing hospitalisation numbers. Balram Bhargava occasionally mentions it in a presser, but there is no systematic release.
- The R-number and the TPR are less relevant today: the omicron variant is highly transmissible and its infectees don’t get tested unless they are overtly symptomatic.
New Delhi: The test positivity rate (TPR) for COVID-19 in Delhi has breached the 5% mark – a threshold that indicates the virus that causes the disease, SARS-CoV-2, could be on the cusp of another outbreak. The R-number is also greater than 2, which means the virus is spreading to two more persons from one infected person – an exponential spread.
But according to the Delhi government’s daily bulletin on April 25, of the 4,168 active cases, only 121 are currently hospitalised. And of them, 32 are in ICUs.
The currently dominant strain of the novel coronavirus – called the omicron variant – has been sending a smaller fraction of its hosts to the hospital than the delta variant did. But this doesn’t mean hospitalisation numbers are useless.
Omicron is not delta
In fact, the significant differences between the effects of the delta and the omicron variants don’t reflect in the numbers that we’re using to track India’s COVID-19 epidemic.
The delta variant, for example, was more able to cause severe disease than the omicron variant currently seems able. So when the delta variant spread, tracking the case numbers and TPR allowed us to anticipate its impact on the population, demand for healthcare, etc.
Many media outlets (including The Wire Science) continue to closely follow the R-number and the TPR. Experts told The Wire Science, however, that it’s time we approached them with abundant caution.
“Comparing TPR and the daily caseload of today with previous times is like comparing apples with oranges,” Brian Wahl, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, Baltimore, said. “The nature of the pandemic has changed, so should the threshold of 5% TPR.”
Wahl is referring to the omicron variant, which is much more transmissible than the delta variant, but less lethal.
Both Wahl and K. Srinath Reddy, the president of the Public Health Foundation of India, also said that a rising R-number could indicate that the number of cases is rising and that that’s helpful to a limited extent. But it can’t provide a qualitative picture of the pandemic today because it is directly related to the number of people being tested.
Because the omicron variant infected a large number of people, because its effects are almost always mild and because testing rates have dropped relative to those during the second wave, it seems likely that few get tested today unless they are overtly symptomatic (with PCR, not the home test).
If there are fewer tests, we miss more cases, which pulls down the R-number. The same thing goes for TPR, Wahl said, because it also depends on the number of people tested.
This said, one number that remains relevant is the hospitalisation rate. “Severe cases indicate how much the healthcare system is strained, and that is more important now,” Reddy told The Wire Science.
But the daily updates from the Union health ministry don’t include hospitalisation numbers. The updates only specify the number of people who tested positive, the number of people discharged and the number of people who have died.
On the other hand, the European Centre for Disease Prevention and Control said in its weekly report of April 21: “The hospital admission rate for the EU … based on data reported by 17 countries was 10.1 per 100 000 population compared to 9.5 [the previous week]. This pooled rate has been stable for one week.”
The ECDC also said 0.8 persons per 100,000 population were being admitted into ICUs, according to data from 12 countries.
Similarly, the US Centres for Disease Control and Prevention website reads: “The current 7-day daily average [for new hospital admissions] for April 13-19, 2022, was 1,582. This is an 8.2% increase from the prior 7-day average (1,463) from April 6–12, 2022.”
In the occasional press conference, Indian Council of Medical Research (ICMR) director-general Balram Bhargava has announced the fractions of people requiring hospitalisation. But such statements have been sporadic. The last time he shared this information was when the third wave was underway in India, in December-January.
There has also been the occasional paper (like this one) discussing in which clinicians discuss the clinical outcomes of hospitalisation from their own centres. But there has been no consistent or systematic effort to collect, organise and release these numbers.
“In terms of judging the pandemic, what we [are] really bothered about is the impact of the pandemic,” according to Reddy. “If mostly the cases are mild, we might not be [very] bothered, but we need to have data to say this.”
(He added that there was the grey-area of long-COVID after an infection – “but this is a separate and evolving science,” he said.)
‘Not easy, but doable’
In April last year, more than 900 Indian scientists signed a petition addressed to Prime Minister Narendra Modi asking the government to release data about the number of people hospitalised and their clinical outcomes into the public domain. They also asked for data on immune response to vaccines and granular data on tests.
Their ask remains unfulfilled to this day.
Giridhar R. Babu, an epidemiologist and a member of The Lancet COVID-19 Commission India Task Force, said collecting hospitalisation data requires a bottom-up approach – where a hospital is required to compile data and feed it into a centralised system. It isn’t easy but it is doable, he said.
“Each patient gets a unique identifier [when they are] admitted. That can be used to track a phenomenal amount of information, including breakthrough infections and reinfection.”
In fact, ICMR created a national registry of COVID patients to collect data on various clinical outcomes. However, only government scientists can access it.
Wahl also recommended wastewater surveillance in the omicron phase of the pandemic, as was recently done in Mumbai and Bengaluru. “This is an innovative indicator. This can shed light on the trajectory of pandemic,” according to Wahl.
He also suggested randomly sampling from within some communities of people to understand if the virus was circulating there. “Even if these exercises pick up [on the circulation], they don’t necessarily say if the disease pattern is severe and if we are in for another wave.”
For this, he echoed Reddy: hospitalisation numbers are key.