Since the first lockdown for COVID-19, Australia has been suffering from tremendous economic and financial damages. Facing the second outbreak, there are some arguing against the necessity of the lockdown by comparing coronavirus with influenza and believing herd immunity can be achieved as simply as with flu. Brett Sutton, Victoria’s Chief Health Officer, commented this notion was “absurd” on 16 July 2020. Comparing COVID-19 deaths to the deaths from an average flu season, “these [COVID-19 deaths] are the deaths you have when you have your controls in place” and if there is no control in place “you get 1,000 cases a day, 10,000 or more cases a day, as has occurred in some countries, and you get up to 1,000 deaths per day, as has occurred in countries in Europe, in Brazil, and elsewhere.”
Herd immunity occurs when 50 to 90% of the population, which depends on how contagious the diseases or viruses are, becomes immune to the infectious disease (Habib 2020). This means people have enough antibodies to fight against the disease through either vaccination or exposure to the virus. Measles, chickenpox and polio are examples of infectious diseases that are no longer common due to achieving herd immunity via vaccines.
Unlike most countries, Sweden’s government did not shut down schools or businesses, and let its people take responsibility to maintain social distancing. The strategy of the Swedish government for reaching herd immunity seems to be the acceptance of a substantial number of infection cases, instead of locking down and sacrificing the economy. However, it didn’t turn out well. It has population of 10.3 million, and there have been 76,492 confirmed cases of COVID-19 with 5,572 deaths until 16 July 2020, according to the WHO. Therefore, the Sweden’s top epidemiologist, Anders Tegnell, replied to the hosts in a radio interview that the country made some mistakes and it would respond differently - perhaps mirroring what the rest of the world had done - if it had more knowledge of the virus in the first place.
A recent research paper published in The Lancet also shows that although with the high impact of COVID-19 in Spain, prevalence estimates are still low - the entire country’s estimated prevalence rate was 5% - and insufficient to provide herd immunity from massive infection (Pollán et al. 2020). This means that in order to achieve herd immunity, we will expect to see more deaths in the susceptible population and overburdening of health systems in the future.
A few studies found only a short duration of immunity after COVID-19 infection, which revealed the difficulty of herd immunity. A research paper in Nature Medicine found that the antibodies in over 80% of convalescent asymptomatic patients and over 60% of those symptomatic with SARS-CoV-2 decrease within 2-3 months after illness onset (Long et al. 2020). Another study also found that 4 out of 8 recovered patients with COVID-19 showed declined numbers of neutralising antibodies 6-7 weeks after infection (Wang et al. 2020). These might indicate COVID-19 recovered patients can be infected again if re-exposed to COVID-19.
Consequently, these studies suggested that maintaining social distance, hygiene, widespread testing, and isolating new confirmed cases and their contacts are the vital actions for epidemic control before a COVID-19 vaccine is developed. Furthermore, one study suggests prolonged or intermittent social distancing may be necessary until 2022 and surveillance should continue until 2024 due to the resurgent contagion (Kissler et al. 2020).
Habib, H. 2020, 'Has Sweden’s controversial covid-19 strategy been successful?', BMJ, vol. 369, p. m2376.
Pollán, M., et al. 2020, 'Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study', The Lancet.
Long, Q. X., et al. 2020, 'Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections', Nature Medicine.
Wang, X., et al. 2020, 'Neutralizing Antibodies Responses to SARS-CoV-2 in COVID-19 Inpatients and Convalescent Patients', medRxiv, p. 2020.04.15.20065623.
Kissler, S.M., Tedijanto, C., Goldstein, E., Grad, Y.H. & Lipsitch, M. 2020, 'Projecting the transmission dynamics of SARS-CoV-2 through the postpandemic period', Science, vol. 368, no. 6493, p. 860.
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