Fragments of Reality
Aim for community immunity, but a question remains unanswered
When the coronavirus that causes Covid-19 first started to spread, nobody was immune to it. Stopping it requires a significant percentage of people to be immune to it. John Hopkins School of Public Health (JHSPH) suggests that if 80% of a population is immune to a virus, four out of every five people who encounter someone with the disease would not get sick. This immunity is sometimes call population immunity or herd immunity. In this way, the spread of infectious disease is kept under control.
JHSPH further suggests that 'depending on how contagious an infection is, usually 50-90% of population needs immunity before infection rates start to decline. But this percentage is not a magic threshold that we need to cross-especially for a novel virus. Both viral evolution and changes in how people interact with each other, can bring this number up or down.' Vaccines help to establish herd immunity.
Measles, mumps, polio and chickenpox are some example for it. However, it has been noticed that sometimes we saw outbreaks of vaccine-preventable diseases in communities with lower vaccine coverage because they didn't achieve herd protection. So, in order to achieve immunity through vaccination, which approach of vaccination is better- bottom up approach or top down approach? Do we know an immunity threshold for Covid-19 disease?
It is clear that national level vaccination programme is not enough for reducing community transmission. We should focus ourselves to achieve immunity within our communities. When we consider the percentage of the population that needs immunity to prevent spread, that percentage is the level required to protect a community. Our shielding mechanism can start from where we live. Our home, neighbourhoods, the places where we come in contact with others from our community, such as store, school and local medical centre, can be considered them under a circle. Such concentric circle, we should aim for immunity. National level lockdown and numerous difficulties in implementing such national programme will deter developing community immunity.
In July 2020 Washington Post published a report titled 'I am not so sure on masks. But here's why I wear one'. The report suggests that for the peace of mind of the neighbours people like to wear mask. However when the directive comes from the Centres for Disease Control (CDC), then as per the report 'can make people feel isolated and lonely and can increase stress and anxiety.' CDC's direction has been considered as knowledge by the population, but empathy is more important than direction in this case.
Psychological reactance theory predicts, injunctions are more likely to elicit counter argument than acceptance. A proverb tells us 'you catch more flies with honey than with vinegar'. Therefore, if it is about taking care of the community, even doubters might decide to take preventive measures. So, we should aim for community immunity and bottom up approach is the best option.
Some population-based studies in Denmark have shown that an initial infection by SARS-CoV-2 is protective against repeat infection for more than six months. But this level of immunity may be lower among people with weaker immune systems and it is unlikely to be lifelong. How can we quickly test whether somebody is immune to the virus? Scientists call the measurement of immunity as 'correlate of protection' (CoP). This means that if you measure the number of antibodies in blood and know the number for which we are protected from virus, then that number is known as CoP.
This is in fact a standard tool in vaccinology. The CoP has been established for other conditions such as influenza and hepatitis, but we need one for Covid-19. Scientists from Hamburg University suggest that it would be difficult for two reasons to trial a new vaccine as the pandemic progresses. First, it would be difficult to find new volunteers without vaccinated or infected. Second, there is an ethical issue of giving unprotected people placebos when good vaccines exist.
CoP would be useful for finding out whether humans are immune to new variant or not. For example, if we know the CoP threshold, then take serum from the blood of vaccinated person that passes the CoP threshold and then see if it can neutralises the new variant. Antibodies can protect against Covid-19, but we do not know the level for which this protection can be achieved. Pfizer vaccine development unit suggests that we might get a number very soon.
What we need to know is the levels of antibodies and T-cells. T cells are a part of the immune system that focuses on specific foreign particles. T cells originate in the bone marrow but are matured in the thymus. However, they are not activated until they find their specific antigen. They bind to this antigen on the surface of antigen-presenting cells. While antibodies latch on to pathogens outside cells and get rid of them, T cells destroy virus-infected cells.
It is true that science is messy and provisional. Science is an ongoing search for knowledge that yields some caveated insights. Science writer Carl Zimmer mentioned that a science article is 'never a revelation of absolute truth. At best it's a status report.' Recently the Scientific American mentioned that 'our review of more than 600 articles about science published in major news outlets from 2013 to 2018 found that most of the write-ups ignored the false starts, trial and error, and serendipity that characterize the scientific process.'
It was also noted that many papers failed to inform the remaining unanswered questions. This unanswered question also remains in case of coronavirus vaccine. We need to find out a measure that shows if we are immune to Covid-19. That will help us to deal with new variants quickly.
Above all, social transmission of knowledge is at the heart of culture and science. we each have more power than we may realize. If communities come together and government machineries engage in those communities directly to provide support through vaccination and other relevant programme that can quickly contribute to immunity. The programme of immunity should not limit only to vaccination but also to implement programmes such as poverty elevation and education. However, a question remain unanswered-What level of immunity prevents re-infection? This question needs to be answered soon.
Dr Kanan Purkayastha is a UK
based Academic, Chartered
Scientist and Environmentalist,
Columnist and Author