Thursday, June 20, 2024

Opening the Pandora’s Box, Covid-19 Vaccine Hesitancy & Prospects for Herd Immunity

In early October 2020, three epidemiologists convened in Great Barrington, a small town in Massachusetts, USA. Jay Bhattacharya (Stanford University Medical School, Stanford, CA, USA), Sunetra Gupta (University of Oxford, Oxford, UK) and Martin Kulldorff (Harvard University, Cambridge, MA, USA) were there to draft an argument for a new strategy to combat COVID-19. They called it the Great Barrington Declaration. It  has since been endorsed by thousands of medical practitioners, researchers, and public health scientists, The Lancet Respiratory Medicine, 2020, reported.

The Great Barrington Declaration acknowledged and stated the following with respect to the lockdowns.

“Current lockdown policies are producing devastating effects on short and long-term public health. Keeping the measures in place until a vaccine is available will cause irreparable damage, with the underprivileged disproportionately harmed…our goal should therefore be to minimize mortality and social harm until we reach herd immunity”, The Lancet respiratory Medicine, 2020.

The authors of the declaration recommended policymakers to adopt an approach they termed “focused protection”. This entailed easing restrictions on low-risk groups, with the intention of allowing them to establish immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through natural infection, while simultaneously stepping up the protection of high-risk groups., Lancet 2020.  For example, governments could fund short sabbaticals for vulnerable workers in public-facing jobs and provide accommodation for individuals who could not easily maintain isolation in their own home.

However, within weeks, an opposing group of experts, also numbering in the thousands, had their names to the John Snow Memorandum. The document, named after one of epidemiology’s greatest historical figures, defended the restrictions to slow the spread of Covid-19 as “essential to reduce mortality, prevent health-care services from being overwhelmed, and buy time to set up pandemic response systems to suppress transmission”.

The John Snow Memorandum described focused protection as “a dangerous fallacy unsupported by scientific evidence” and warned that “uncontrolled transmission in younger people risks significant morbidity and mortality across the whole population”. The memorandum concluded by asserting that “controlling community spread of COVID-19 is the best way to protect our societies and economies until safe and effective vaccines and therapeutics arrive within the coming months”.

“The Great Barrington Declaration was also criticised notably by one Walensky who in his interview with The Lancet Respiratory Medicine, 2020 is quoted as having said “the declaration predicated on the idea that you know who is going to get sick and you can somehow isolate and protect them, but there is absolutely no evidence that we can do this”. Walensky, according to the Lancet Respiratory Medicine, 2020, also criticised the declaration arguing that it was not straightforward to identify those on co-morbidity that makes them vulnerable to the ravages of Covid-19.

“No-one is suggesting that lockdowns should be the default position. They are a last resort. But if we just let the virus run free without mitigation strategies, such as masking, our hospitals will overflow and that would mean we would no longer be able to take care of the population’s health across the board”, Walensky told The Lancet Respiratory Medicine

However, it is important to note that the drafters of the Great Barrington Declaration stressed that they were not suggesting people behave recklessly. They observed that basic precautions such as handwashing and self-isolation, when necessary should be maintained. The priority being to dismantle many of the constraints that were imposed globally. The Declaration advocated resumption of sports and cultural events, re-opening of business and other business and discouraged young low risk adults to discontinue working from home.

In an unprecedented effort, scientists from all over the world have come together to rapidly develop a vaccine for COVID-19 (Callaway, 2020). Vaccines have historically proven to be highly successful and cost-effective public health tools for disease prevention (Rémy et al., 2015), and already by April 2020 more than 100 COVID-19 vaccine candidates had been developed.

However, Fine et al, 2011 noted that the effectiveness of a vaccine in controlling the spread of COVID-19 depends on the uptake level of the vaccine in the population. A sufficiently high uptake of an effective vaccine ensures protection for those vaccinated and may end the pandemic by generating herd immunity, thereby protecting everyone, including those still susceptible to the virus.

The term `herd immunity’ is increasingly frequently seen in recent literature on the epidemiology of infectious diseases and on their prevention and control by immunisation. The term Herd Immunity has been used by various authors to conform to different definitions. It is defined as “the reduction of infection or diseases in the unimmunised segments as a result of immunising a proportion of the population”, (Monica N, 20).

Herd or community immunity is established when a large part of the population within an area becomes immune to a specific disease and the infectious agent will stop spreading. As not each single individual is immune to the infection, the population as a whole offer’s protection. This happens because, proportionally there will fewer high-risk individuals in the entire population. Therefore, the infection rates decrease, and the disease gradually fades out, (Monica N, 20)

Herd immunity cannot be obtained concomitantly in many geographical areas because the areas have different population density and the societal measures to contain the spreading are different). The societal tactics to achieve the much-needed herd immunity should be developed keeping in mind the welfare of the population.

A proportion of 50–66% of the population needs to be immunized naturally or artificially in this SARS-Cov2 pandemic and this percentage is not easily achievable, (Monica Neagu, 2020). The duration of herd immunity is another issue while information on the long-term immune response against SARS-CoV2 is yet scarce.

It has been noted by scholars that herd immunity can also be achieved naturally by recovering after the disease or artificially through vaccination. After infection and recovery, the immunological memory will be sustained by memory immune clones that, if subsequent exposure to the same antigen occurs, will expand and protect the individual from the same infection.

According to, (Monica N, 20), the percentage needed for a community to reach herd immunity depends on the basic reproduction number (R0). R0 describes the average number of people that a single-infected person can infect nonimmune people. The higher the R0, the more people need to be resistant to reach herd immunity, (Kirtiman S, 2020). For example, for a R0 less than one, the infectious disease spread will die out on its own, (Heffernan JM et al, 2005).

The 1918 Spanish flu pandemic that spread to one third of world’s population and had a death toll of 50 million had an R0 of 1.8., (Biggerstaff M et al 2014), For SARS-Cov2, it was calculated that R0 is in the range of 2–3. (Liuy et al 2020)Therefore, for these numbers a range of 50–67% of the population must be resistant so that herd immunity acquirement would drop the infection rates, (Zhao S et al 20).Vaccination is a way to stop infectious diseases and this endeavour to build herd immunity was verified in many other infectious diseases. 

The literature, also indicates, several hurdles which are prevalent in fighting SARS-C0V2 infection and moreover in establishing the intended herd immunity. First, it is an unknown or less known infection within the coronavirus family. Being new in humans, everyone is susceptible to infection now as there is no existing immunity to build on. Another issue is that even after recovering from infection, it is unknown how long the protection will be conferred or how long the immunological memory will last or more specifically how long the herd immunity is in action for that matter, (Monica S, 20).

A barrier to reaching herd immunity is the prevalence of people who refuse or are hesitant to take vaccines (MacDonald, 2015). The World Health Organization (WHO) named vaccine hesitancy one of the top 10 threats to global health in 2019 (WHO, 2020a). While vaccine hesitancy is growing, hesitancy is not equivalent to refusal many people who are vaccine hesitant do not entirely refuse vaccines. Instead, they either delay vaccines or are willing to take some vaccines but not others (Dube et al., 2013). Also relevant for a COVID- 19 vaccine is the observation that people are more likely to reject new vaccines than familiar ones (Dube et al., 2013).

The road to achieve herd immunity will not be identical in different geographical areas. There are various factors and several hurdles’ to be solved in order to achieve herd immunity. A vaccine for COVID-19 might be the best hope for ending the pandemic and induce herd immunity to prevent future outbreaks. However, the challenge to extinguish the novel coronavirus does not end with finding an effective vaccine. 

Knowing why people are hesitant to accept Covid-19 vaccine may enable design of more effective efforts to increase the overall level of uptake in the general population. This may also help government agencies; health care workers and other authorities mitigate the impact of vaccine avoidance. Such efforts may involve developing policies and a preparedness for vaccine avoidance. Mishandling of public expectations at any point may lead to an avalanche opposition which might be unrecoverable.

Thabo Lucas Seleke is a Researcher & Scholar, Global Health Policy Analysis (LSHTM),

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