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Can herd immunity solve Covid-19?


Pedestrians wearing protective face masks, following an outbreak of the coronavirus disease, walk on the crossing at Shibuya shopping and amusement district in Tokyo, Japan March 31, 2020. Reuters

Pedestrians wearing protective face masks, following an outbreak of the coronavirus disease, walk on the crossing at Shibuya shopping and amusement district in Tokyo, Japan. Reuters

Herd immunity refers to the protection from a contagious disease that is conferred on an entire population because enough of its people are immune to the disease. Many viral and bacterial infections including Covid-19 spread from person to person. This chain is broken when a sufficiently high percentage of the population is immune to the particular virus or bacterium because the microorganism won’t have enough eligible hosts to enable it to perpetuate itself. The virus or bacterium will thus die out.

How do you get immune to a viral infection like Covid-19?

There are two ways you can get immune to a viral infection—through natural immunity or through a vaccine. Natural immunity occurs when you become immune to a specific disease after contracting it. The entry of a new pathogenic virus into your body causes certain cells of your immune system to make antibodies against the virus. These antibodies are designed to help kill the virus. In addition, the same cells will retain the image of the virus in their memory such that if you get infected with the same virus again—assuming of course that you survived the disease—it can immediately produce antibodies that can attack the virus before it spreads and makes you ill. In other words, surviving an initial attack of a viral disease gets you immune to the disease.

The other way you can get immune to a viral infection is by vaccination. A vaccine contains material that resembles a disease-causing microorganism such as a weakened or dead microbe, its toxins, or one of its surface proteins. The measles vaccine, for example, contains weakened measles viruses, which when introduced into your body, will not make you sick (because the viruses are weakened) but it tricks the cells of your immune system to think that it is the real McCoy, and then react by producing antibodies against the virus while at the same time retaining the image of the virus so you get protected from future attacks of the measles virus.

How can we achieve herd immunity to Covid-19?

Illustration of herd immunity. Photo courtesy of USA Today

Illustration of herd immunity. Photo courtesy of USA Today

We can simply do nothing and allow the disease to freely circulate globally. In time, enough of the world’s population will have been infected by the disease and the world attains herd immunity. But, obviously, this is not an option because this way, millions will have to die before worldwide herd immunity is achieved.

The other and only real option is mass vaccination, which confers herd immunity without anybody dying or getting sick. Unfortunately, there is no vaccine for Covid-19 yet, but hundreds of research labs all over the world are working on it. At the moment, more than 20 promising vaccines are under development.

But despite the sense of urgency under which the research labs are working, it seems like it will be 12 to 18 months before a vaccine (although a team in England claims they can have a vaccine by September) will be available for mass immunization. It takes time to produce a new vaccine because vaccine development is a complex multi-stage process.

How many in the population must be vaccinated to achieve herd immunity?

The percentage of the population which must be immunized in order to achieve herd immunity varies for each disease. For highly contagious diseases, the required figure is high. Measles require 90 to 95 percent immunization coverage to achieve herd immunity while polio requires 80 to 85 percent. As for Covid-19, this remains to be determined.

Herd immunity through vaccines is not a pipe dream

We have already eradicated a disease, smallpox, a highly contagious and fatal disease by achieving herd immunity. After an effective smallpox vaccine was developed, a worldwide immunization campaign was undertaken such that by the late 1970s, worldwide herd immunity for the disease was attained. The World Health Organization (WHO) certified the global eradication of the disease in 1980.

In the Philippines, we have likewise achieved some level of success in establishing herd immunity for polio. In the 1990s, our polio immunization campaigns were so successful that our country was certified polio-free by the WHO in October 2000. Sadly, last year, polio has re-emerged in our country, which goes to show that after attaining herd immunity, immunization rates need to be maintained at a required level, otherwise herd immunity can break down and lead to a surge in the number of new cases.

Source: Manila Bulletin (

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