Over the past few weeks, the country has been dreading the possibility that the novel coronavirus outbreak will move to the stage of community transmission. What is community transmission, and how does a pandemic progress to this stage?
Coronavirus: What are the stages of a pandemic?
In the first stage of a disease epidemic that eventually takes the form of a pandemic sweeping the globe, cases are imported into a country in which the infection did not originate. An infection whose spread is contained within the boundaries of one or a few countries is obviously not a pandemic. The first case of COVID-19 outside China was reported in Thailand.
The second stage is when the virus starts being transmitted locally. Local transmission means that the source of the infection is from within a particular area and the trajectory the virus has taken from one person to the next is clearly established.
The third stage is that of community transmission. According to the World Health Organisation (WHO), community transmission “is evidenced by the inability to relate confirmed cases through chains of transmission for a large number of cases, or by increasing positive tests through sentinel samples (routine systematic testing of respiratory samples from established laboratories)”. In layman terms, it means that the virus is now circulating in the community, and can infect people with no history either of travel to affected areas or of contact with an infected person. If and when community transmission happens, there might arise the need for a full lockdown because in that situation it is theoretically possible for every person, regardless of where they are from and who they have been in contact with, to spread the disease.
Community transmission is usually localised; one state can record it. For example, the UK reported community transmission in Northern Ireland.
There is also a fourth stage in every pandemic. It is when the disease, COVID-19 in this case, becomes endemic in some countries. The Indian government’s containment plan takes this possibility into account. Among diseases that are currently endemic in India — meaning they occur round the year across the country — are malaria and dengue.
How does categorising an outbreak in this manner help?
The stages of a pandemic are uniform the world over. This is so because in today’s interconnected world, it is important to have a standardised phraseology that conveys the same thing to every person around the world, and helps countries prepare better.
The categorisation helps countries take specific actions that are necessary to target just that particular scenario.
For example, India imposed travel restrictions to China from very early on as the cases then were all imported from China. Later, as cases started being imported from other European countries, flight and visa restrictions were put in place for those countries. India has now shut itself to individuals coming from all countries — this is because the virus is now confirmed as circulating in at least 177 countries and territories.
However, there are also cases of local transmission — that is why large numbers of people are in government quarantine facilities, in home quarantine, or under community surveillance. The official position in India is that no community transmission has been detected, inferred from the testing of over 1,000 random samples taken since February from people who had symptoms like COVID-19, but no travel or contact history. None of them, according to the Indian Council of Medical Research (ICMR), has tested positive for novel coronavirus.
Are these stage categories watertight?
Scientific definitions are usually very precise, but classifications can also draw on informed judgment. For example, the transition from one pandemic stage to the next is something that can happen in a day, but a lone case would probably not be the basis of such a declaration.
That is also why, even though the Health Ministry had released a statement some days ago on the evidence of “community transmission” in Agra, scientists say it was not classic community transmission, but local transmission at the community level. There have to be more of these cases of infection from untraced sources for the outbreak to move on to the next stage.
However, as the number of cases increases, so also do the chances of transition to the community transmission stage. States would have different approaches to fighting the disease, and that would impact neighbouring states as well.
Worldwide, in which stage is the COVID-19 pandemic now?
The pandemic has spread to nearly every country on the planet. In most, though, it is in the stage of either imported cases or local transmission. Among the countries where community transmission seems to be operating are China, Italy, Iran, South Korea and Japan. China adopted a graded approach in dealing with the infection but the epicentre, Hubei, was in a state of complete lockdown at the peak of the infection — something that Italy has now effected in a bid to stop the virus from wreaking more havoc, given the country’s ageing population. South Korea has brought down infections with mass free testing and treatment. For imported cases, vigilance at the borders and airports suffices.
The escalation pattern in countries has differed as much as their response. Assuming that reports of the first case having occurred in November are true, China took almost a month to escalate to a stage where the outbreak became a global concern. Community transmission would like have started already.
Italy, on the other hand, took just a few days to reach that stage. The European Centre for Disease Prevention and Control says: “The speed with which COVID-19 can cause nationally incapacitating epidemics once transmission within the community is established, indicates that in a few weeks or even days, it is likely that similar situations to those seen in China and Italy may be seen in other EU/EEA countries or the UK.”
How long before India enters community transmission?
Nobody knows. Dr Balram Bhargava, secretary, Department of Health Research and D-G, ICMR, has said that community transmission is inevitable; other experts feel it may have already happened.
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Dr Anurag Agarwal, Director, Institute of Genomics and Integrative Biology, said: “In India so far, we have found an explanation for every case, so there is no background community transmission yet. But we do not really know how this will pan out. There are some reports of one strain having less mortality. If indeed a milder strain has come to India, it could change the course of the epidemic. There is another theory that all the various viruses circulating in South Asia and the generally lower levels of hygiene may give us some immunity. This is an evolving phase; we have not done badly so far. But there is more to come.”
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