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Current Affairs

WHO says achieving herd immunity naturally is dangerous

Date: 19 May 2020 Tags: Miscellaneous

Issue

The World Health Organization has condemned the “dangerous” concept of herd immunity for managing the coronavirus (COVID-19) pandemic.

 

Background

The concept of herd immunity is generally used for calculating how many people will need to be vaccinated in a population in order to protect those who are not vaccinated.

 

Details

  • It was mistakenly assumed that as this disease spreads across the world, only the severe cases become apparent while most people would indeed be infected as reflected in sero epidemiology results.

  • Greater proportion of people getting infected would mean that the pandemic will be over soon and people can go back to normal business.

  • But the preliminary results from in sero epidemiology studies are showing the opposite. The proportion of people with significant clinical illnesses is a higher proportion of all those who have been infected.

  • This is because the number of people infected in the total population is probably much lower than we expected.

  • While antibodies (IgG and IgM) against novel coronavirus generally develop in one–three weeks after infection, some people do not seem to develop a humoral immune response, as reflected by detectable antibodies. It is unclear why this happens. 

  • Though a small study involving just nine patients found a direct correlation between clinical severity and levels of antibody response, antibody detection and higher titers have not always been found to correlate with clinical improvement in COVID-19. Also, mild infections can resolve even before detectable antibodies are produced.

  • Also, how long neutralising antibodies against the virus would last is currently not known. In the case of the 2002 SARS, levels of IgG remained high for nearly four–five months before declining during the next two–three years. For MERS, the antibodies persisted for up to 34 months.

  • Reinfection is mightily possible with at least three of the four coronaviruses which cause common cold. The reasons for this reinfection are not fully known, but evidence suggests that possibilities include both short-lived protective immunity and re-exposure to genetically distinct forms of the same viral strain.

  • A well-designed longitudinal study involving those who have recovered from COVID-19 for recurrent illness can help provide the much-needed information about reinfection and the duration of protection by the antibodies.