1.4 Possible Responses to COVID-19
By Judith Glynn
Professor of Infectious Disease Epidemiology, LSHTM.
In deciding how to respond to the COVID-19 pandemic, policy makers have to weigh up the available evidence and look at the pros and cons of different approaches.
The most appropriate response will depend on the stage of the epidemic.
Keeping the Virus Out
The first stage is to try to keep the virus out of a country. But that is extremely difficult. People are infectious before having symptoms of COVID-19, so symptom screening will not detect everyone who is infectious. The only way to
keep the virus out is limiting travel, and having strict quarantine rules (e.g. all people coming in to a country have to stay isolated for 14 days). This is helping some countries (e.g. Hong Kong, China, New Zealand). Note that although
travel restrictions are widespread, they will have little effect if the disease is already established in a community.
Containment: Contact Tracing
The next stage is to try to isolate everyone who tests positive or has symptoms suggesting COVID-19, and do contact tracing of people they’ve recently come in to contact with. This means identifying any contacts that your focal individual
could have infected, and testing them, or asking them to isolate themselves. If any of the contacts test positive, you must also perform this contact tracing step on them (i.e. trace their contacts).
But to be effective you would need to be able to identify who to isolate. And because people without symptoms can be infectious you would need wide-scale testing to find them. This has been attempted in many places, but has usually not been able to keep
track of the infections.
Once infection is widespread there are several theoretical options:
Do nothing and rely on herd immunity
If you let the epidemic run its own course without taking steps to control it, infections would increase quickly to a peak and then start to decrease as an increasing proportion of the population becomes immune. This would
get the worst of the epidemic over quickly, and leave a population with substantial immunity. But there are two critical problems.
The first problem is that a very large proportion (around two thirds) of the population would need to get infected if you rely on herd immunity alone to reduce transmission (this is explained in step 4.2). Even if only
1% of cases die, in a population that would be a lot of deaths. In the UK with a population of 60 million, if 2/3 were infected that would be 40 million people, and 1% dying would mean 400,000 deaths.
The other problem is that a large number of people would get ill within a short space of time. So, hospitals would be overrun and treatment would be very limited. Many of those who would have survived with hospital support would die, leading to many more
than 1% dying.
Shielding: Protect the most vulnerable
Some people are more vulnerable to COVID-19 than others (step 3.1). Particularly the elderly and people with certain underlying conditions including heart disease and lung disease. If people who are more at risk are shielded, the deaths could be reduced.
In the UK, people over 70 years old, or who have an underlying health condition have been asked to shield themselves. This means staying home, and minimising contact with other people (e.g. asking friends to collect groceries and prescription medicines
for you). By minimising contact with others, we can reduce the chances that these groups will become infected and fall ill.
But it is not easy. For example, vulnerable people may be exposed in multigenerational households (i.e. grandparents living with their grandchildren). They may live in care homes, or need to go outside to visit hospitals when receiving health care for
Reducing Transmission through Changes in Behaviour
Try to reduce transmission to all –using hygiene, physical distancing and lockdown
As well as protecting the most vulnerable, a whole population approach is needed, to reduce the chance of transmission.
Hygiene advice (handwashing with soap, coughing/sneezing into elbows, hand sanitisers, avoid touching your face) and
avoiding close contact are simple and cheap and should be universal (see step 2.2). Facemasks may also help (see step 2.3).
Figure 1. Two people wearing face masks and standing 2 metres away from each other. Image credit: Studiogstock
Further ways to increase physical distancing include closing all non-essential places where people come together (cinemas, bars, some shops, sports venues, places of worship); closing schools and universities; avoiding any gatherings that bring people
together from different households; working at home if possible; staying at home except for essential trips. Different countries have imposed “lockdowns” with different degrees of strictness (steps 3.2, 3.6).
Lockdowns reduce transmission but have huge impacts on the economy and on individuals and cannot be continued indefinitely.
How and when to release lockdown
Lockdowns can reduce transmission to a point when other strategies, such as containment (test, contact trace and isolate), can be used again. Releasing lockdown does not mean letting the epidemic run
unchecked, or cases will accumulate again very quickly, giving a second wave.
Relaxing lockdown needs to be done slowly, so that it can be paused and even reversed if infections start to rise again. This could be done sector by sector, and/or by area, and/or by section of the population (see step 4.7).
Relaxing lockdown should be done together with other control measures – continued hygiene practices, shielding of those at increased risk, and testing.
At all stages of the epidemic, testing for the disease is key. This will tell you whether your containment strategies are working, and where there are outbreaks of new infections (see step 3.4).
Contact tracing: the process of identifying people who may have had contact with an infected individual (“contacts”), testing them for infection, treating the infected and tracing their contacts in turn. The public health aim being to
reduce infections in a population.
Epidemic: widespread occurrence of an infectious disease in a large number of people in a short period of time.
Herd immunity: the protection given to a population against an outbreak of a specific disease when a high percentage of the population have gained immunity against it.
Immunity: when a person is not likely to get a disease because they have already been infected, or from a vaccine they are said to be ‘immune’.
Pandemic: an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.
Pathogen: Microorganism that causes disease.
Transmission: The spread of infection, for example by touch, food, water, droplets, air.
Vaccine: Substances containing disabled versions or pieces of a particular pathogen, usually given via injection. Vaccines stimulate the body to produce antibodies to provide immunity against that pathogen.
Virus: An ultramicroscopic infectious non-cellular organism that can replicate inside the cells of living hosts.
1. An introduction to social distancing and herd immunity: https://www.washingtonpost.com/graphics/2020/world/corona-simulator/
2. A simple guide to contact tracing:
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