Getting Technical
Continued from page 43
confer immunity to the virus itself – it only reduces the risk that vulnerable people will come into contact with the pathogen ”.
PREVIOUSLY ACHIEVED HERD IMMUNITY FOR OTHER INFECTIOUS DISEASES Measles , mumps , polio , and chickenpox are prime examples of infectious diseases that were very common but are now rare mainly because vaccines have been developed which have been effective in establishing herd immunities .
“ Once a sufficient proportion of the population is no longer susceptible to the virus , any new outbreak diminishes and then peters out .”
However , there have been sporadic outbreaks of vaccinepreventable diseases in communities with lower vaccine coverage because , at the times of infections , they did not have sufficient protection . A prime example of this is the measles outbreak at Disneyland in 2019 . Viruses tend to mutate so antibodies from previous infections provide protection for only relatively short periods of time , for example protection against flu is usually less than a year . If SARS-COV-2 , the virus that causes Covid-19 , is like other coronaviruses that currently infect humans , it can be expected that people who have been infected will be immune for months or possibly years , but probably not for their entire lives .
There are two main methods of achieving herd immunity : either a sufficient proportion of the population becomes infected or is deliberately dosed with a protective vaccine . At worst , the virus can infect so many people in just a few weeks that hospitals could be overwhelmed with consequential high death rates as happened at Manaus in Brazil . At best , current levels of infection are maintained or even steadily reduced until a vaccine becomes available . However , continued physical distancing for an extended period of a year or longer on the part of the entire population is often needed .
Restrictive social distancing measures can only be reduced after the number of infections has declined , but they may need to be re-implemented if numbers increase again . Even so , SARS- COV-2 can still infect children before they are vaccinated or adults after their immunity has waned . However , in the longer term , the explosive spread that has happened recently is unlikely because much more of the population will be immune by then .
Similarly , the earlier description as to why letting herd infections ‘ just happen ’ is not a good idea , deliberately getting infected with SARS-COV-2 to ‘ get it over with ’ is not a course which should even be contemplated .
Previously , for some other diseases , such as chickenpox before the varicella vaccine was developed , people did sometimes expose themselves intentionally as a way of achieving immunity . Generally , for less severe diseases , this method might be acceptable but when SARS-CoV-2 is involved any Covid-19 content includes much higher risks of disease , or death .
Anticipated death rates for Covid-19 have not yet been fully determined but current data suggest they will be around 10 times higher than for the flu and higher still where vulnerable groups like the elderly and people with weakened immune systems are involved .
As already mentioned , the current physical distancing measures will not always need to be as strict as the present ‘ shelter-in-place ’ directives are . Thanks to extraordinarily intense actions already taken on a global scale , encouraging news in the overall grim Covid scenario is that newly developed and tested vaccines are now being widely distributed with their effectiveness fully maintained by another modern technology – reliable refrigeration . RACA
QUOTE OF THE MONTH
Projects we have completed demonstrate what we know . Future projects decide what we will learn .
- Dr Mohsin Tiwana
www . hvacronline . co . za RACA Journal I June 2021 45