A Review by Steve Cingapagu
With much of the world in lockdown, the effectiveness of social distancing measures is being questioned as epidemiologists ponder if we should resort to herd immunity. As cases continue to increase and a vaccine is yet to be found, the question is how long can social distancing remain an effective preventative measure? And at what cost?
Herd Immunity:
Herd immunity is the immunization of a large proportion of the population to prevent the spread of a pathogen and as a result protect the vulnerable members (e.g. aged, those with weak immune systems, those taking immunosuppressant drugs, etc.)
This can be achieved in two ways: either through vaccination or through exposure to the live pathogen.
(Kucharski, A 2017)
For COVID-19, the R0 is 3.5, meaning that an estimated 70% of the population needs to be immune to prevent the spread.
Vaccination:
Vaccinations work by injecting a live attenuated or dead form of a pathogen into the body which stimulates the production of antibodies against that pathogen. Therefore, during the live infection, the relevant antibodies are rapidly produced because of memory cells, which destroy the pathogen and prevent you from falling ill.
(Source: Lumenlearning)
This graph shows the rapid increase of antibodies after a second exposure (live pathogen) which protect you from contracting the illness.
This method of developing immunity and preventing the spread of a disease has been used in the past and has proved to be very effective.
During the 20th Century, the US was heavily hit by measles. Dr. John Enders and his team were keen on developing a vaccine for it. It took them many months to culture the measles virus. They first carried out pre-clinical testing on monkeys and was shown to induce an antibody response. They then carried on to clinical trials, and a vaccinated group of children who tested positive for antibodies were monitored. It was observed that although exposed to the virus, they did not contract measles. Nationwide trials were conducted and in 1963, the vaccine was made available to the public. Finally, in 2000, the US was declared measles free. (John Enders et al 1964)
(Source: The history of vaccines)
From this graph, we see that from 1964 (470,000 cases) to 1965 (265,000 cases), there was a 43,6% decrease in reported cases. Furthermore, the number of cases in 1981 was only 1/5th the number of cases the prior year: a significant drop. These numbers model the effect of the vaccine. Furthermore, the R0 for measles is around 18, which is much higher than for COVID-19. And if the US managed to eradicate measles, eradication of COVID-19 is very much possible.
Furthermore, there was a measles outbreak in 2014 at Disneyland. Of 110 California patients, 45% were unvaccinated, 47% had an unknown vaccination status, 5% had one dose and the rest had 2 or 3 doses. There is a clear link (as shown by these numbers) between a lack of immunity and contraction of the illness. Due to the possibility of a future outbreak, immunity must be developed even against COVID-19, which will reduce deaths in the long run. Immunity is key. (Zipprich, J 2015)
Furthermore, Olav Hungnes, a Norwegian virologist said, “Even though many acquired immunity through infection, we believe that vaccination may have been responsible for most of the increase. The population of Norway is particularly well prepared for major new outbreaks of swine flu, compared with countries where fewer received the vaccine. Even those who are not immune will benefit from the fact that the spread of infection would be slowed by others' immunity -- we call this herd immunity”. (Infection control today 2010)
Whilst a vaccine may seem promising there are a few hurdles. Firstly, the development of vaccinations can take many years. It took nearly 40 years to eradicate measles from the US; how many years will it take to eradicate COVID-19 from the whole world? In addition to this, with borders closed and rising political tensions, the distribution of the vaccination may be hindered.
Naturally:
Immunity through exposure to the virus has never been adopted by any country on a large scale before. However, Sweden is making use of this technique, and it seems to be quite effective, judging by the numbers. They have 483 deaths/million, as opposed to countries implementing social distancing-UK (611), Italy (566) and, Spain (588) (Numbers are as of 13-6-2020, Coronavirus Updates). However, there is always the possibility that other factors like geographical location, number of tests per million, and the quality of tests may be influencing these numbers.
One possible solution to this pandemic is to expose young and healthy individuals who have no immune defects to the live virus in small batches, which will help develop antibodies and at the same time be manageable to health care systems. However, experts at John Hopkins Bloomberg School of Public Health say that COVID-19 immunity is far off. They suggest that exposure to the live virus doesn’t lead to antibody development. Even if it does, immunity will last only for a few months. (D’Souza, G and Dowdy, D 2020) If this is true, evidently immunity through exposure is not an option as it will require individuals to be re-infected multiple times to maintain immunity, which can lead to multiple deaths and in the end, a very short-lasting immunity.
Social Distancing:
Maintaining distance from other individuals (6-8 feet advised) to prevent the spread of the pathogen. This has been achieved through nation-wide lockdowns, banning public gatherings, cancelling sports events, closing schools, offices, malls, etc.
During the 1919 Spanish flu outbreak, two cities in the US, Philadelphia and St Louis had very different outcomes, and it all depended on social distancing.
St Louis issued a lockdown 2 days after the first reported case while Philadelphia, 10 days after their first reported case hosted a parade that was attended by over 200,000 people. Resultantly, St Louis had only 358 deaths per 100,000 and Philadelphia had 748 per 100,000. St Louis was estimated to have cut transmission rates by 30-50%. These numbers depict the effectiveness of social distancing in preventing the spread of pathogens.
(Strochlic, N and Champine, R.D 2020)
(Source: Michael J Koren, qz.com)
The peak deaths per 100,000 for St Louis was 75 as opposed to Philadelphia’s 265. We can see that social distancing has reduced the number of cases and deaths by cutting transmission.
A study published by the Proceedings of the National Academy of Sciences showed that cities that lifted restriction too early were hit by a deadly second wave (St Louis), while cities which maintained restrictions (New York) did not experience one.
(Strochlic, N and Champine, R.D 2020)
An important aspect of social distancing is timing. When to introduce and when to lift restrictions is a challenge which accompanies the implementation of social distancing and is one of the major questions which countries world-wide are wrestling with.
(Source: Umair Khan, vox.com)
This graph shows the cumulative frequency of cases in relation to number of days without social distancing, with it and with it if implemented one day late. The graph without social distancing skyrockets up, while the other two graphs with social distancing flatten. However, with just one day delay, there are 40% more cases, which models the importance of timing when it comes to social distancing.
There are, however, some cons with social distancing:
Leads to poor mental health-OCD, paranoia, depression, anxiety and lockdowns have led to many suicides.
Strains the economy.
Financial loss e.g. salary cuts.
Increased unemployment.
The mental health of individuals must be considered while implementing social distancing. There is a trade-off between the mental health and the transmission of the pathogen-physical health.
The aim must be herd immunity through a vaccination. We have seen that a lack of immunity will lead to future outbreaks, so immunity is key. This shouldn’t be achieved through exposure to the live virus because it burdens health care systems, leads to high mortality rate and can potentially lead to a very short-lasting immunity. Vaccinations, however, can be given multiple times without leading to death. Therefore, immunity may be gained.
Till then, social distancing measures must be put in place to reduce cases in the short run and to ease burden on health care systems. Of course, the mental health of individuals must be considered, which means instead of a full lockdown, there should be curfews and limitations (e.g. limited parking slots at malls.) This does compromise on the transmissibility, but this is the challenging trade-off with mental health and seems to be the best way to move forward.
References:
Kucharski, A(2017) ‘What is Herd Immunity?’ URL: https://www.youtube.com/watch?v=cEn1PKyBUNc&t=15s Date viewed: 21-5-2020
Enders, A, colleagues, Stokes, M, Stokes, Stokes Jr, US public health service (1964), ‘Mission Measles-The Story of a Vaccine’ URL: https://www.c-span.org/video/?458170-2/mission-measles-story-vaccine Date viewed: 22-5-2020
Zipprich, J(2015) ‘Measles Outbreak-California, December 2014-February 2015’. URL: https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6406a5.htm Date viewed: 22-5-2020
(2010). ‘Herd Immunity to H1N1: The Norway Experience’. URL: https://www.infectioncontroltoday.com/view/june-2020-bug-month Date viewed: 22-5-2020
‘Coronavirus Updates’. URL: https://www.worldometers.info/coronavirus/ Date viewed: 13-6-2020
D’Souza, G and Dowdy, D(2020). ‘What Is Herd Immunity and How We Can Achieve It With Covd-19’. URL: https://www.jhsph.edu/covid-19/articles/achieving-herd-immunity-with-covid19.html Date viewed: 23-5-2020
Strochlic, N and Champine, R.D(2020). ‘How some cities ‘flattened the curve’ during the 1918 flu outbreak’. URL: https://www.nationalgeographic.com/history/2020/03/how-cities-flattened-curve-1918-spanish-flu-pandemic-coronavirus/ Date viewed: 24-5-2020
Edited by: Ashna Chaturvedi and Noelle Darts
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