LIFE IN THE TIME OF COVID-19

‘Herd Immunity’ Will

Happen – But When?

By RICHARD STERNBERG • Special to www.AllOTSEGO.com

We have heard the phrase herd immunity frequently and it has been used as if it has some sort of magical powers to free us from the scourge of COVID-19. But what exactly is it and how does it work?

Herd immunity is the concept that when a high enough percentage of a population has immunity to a disease, either by developing immunity naturally through exposure or through vaccination, the probability of any one remaining individual contracting the disease decreases.

Actually, this should be a fairly simple concept. When there is less of the disease around to catch and fewer targets, the spread slows down. The point where a population has enough people immune to very significantly slow the spread is the point where we say we have herd immunity for a disease.

The point we reach herd immunity differs based on the infectiousness of a disease, the behavior that leads to its transmission, and the rate of transmission we find acceptable. We still don’t know the risk of contracting COVID-19 if exposed to the SARS-CoV-2 virus or the amount of virus needed to trigger a reaction to it.

Currently, we hear things such as, “Once 70 percent of the population has been exposed, we will have herd immunity.”

Other places, I have read numbers as low as 20 percent (highly wishful thinking) and as high as 90 percent.

The truth is an individual’s risk does decrease as the percentage immune around her increases, but it doesn’t hit zero until she is immune either by having contracted the disease or by immunization.

The disease doesn’t go away until the percentage with it reaches zero, which is termed eradication. For example, worldwide we are so close to eradicating polio, but until the last cases have recovered without any further transmission the population is not safe and new generations can get the disease.

The same is true with COVID-19.

What it comes down to is: Herd immunity is the point where the transmission rate of the disease is so low and so few people are contracting it that society as a whole accepts the remaining cases as being inevitable.

Measles as a disease was mostly eradicated in the U.S. by aggressive immunization programs for decades beginning in the ’60s.

Measles kills. But as herd immunity developed, some parents refused to have their children vaccinated, thinking that if everybody else’s children were vaccinated there would be nobody for their child to catch it from.

Unfortunately, too many people thought this way. Measles is very highly contagious, probably more so than COVID-19, and a big enough reservoir of the non-immunized was now left that occasionally it takes off.

It can be fatal and children died (unnecessarily). You have probably heard or read about this in the media in the last few years. The same will happen with COVID-19, unless the percentages immune become very high.

So, if we take 70 percent as the point where we declare herd immunity, then 240 million Americans will have had to contract it. At an overall fatality rate of between 0.5 and 1.0 percent (this includes minimally and asymptomatic people who are still infective anyway), we can expect 1.2-2.4 million Americans to die.

There will still be 90 million people at risk.

We need to slow the spread and pray for a vaccine soon to avoid this result. Wear your masks. And to the people who claim that they can’t wear a mask (don’t get me going on that), wear a face shield. It works as well and doesn’t interfere with your breathing.