MATTER OF TIME
How soon will herd immunity come and normalcy returns?
Declining COVID-19 case numbers and rising vaccination numbers are signs that an end to the pandemic is in sight.
But when exactly that happens depends on reaching herd immunity.
“Herd immunity pertains to the percent of a population that is immune to a disease,” said Dr. Debra Powell, chief of the division of infectious disease and medical director of infection prevention at Reading Hospital-based Tower Health. “Depending on how many cases each new case produces, you may need a higher number (to reach herd immunity).”
Diseases with a high reproduction number need a large percentage of the population to be protected against the virus to reach herd immunity. The reproduction number is how many new cases form from every one case.
Earlier this year, Powell and another doctor said every case of COVID usually produces two to three new cases.
“You need that high percentage to protect the people who can’t get the vaccine or who have never had the disease from getting infected,” Powell said. “Some of the estimates for herd immunity for this infection I’ve seen as low as 70%, which I think is probably too low, and as high as 90% depending on the variants that are currently circulating.”
Powell believes at least 80% of the population needs to be protected against COVID to reach herd immunity and allow a return to normal life. Once a large percentage of the population is protected, the virus has fewer people to infect and then is no longer circulating in
"You need that high percentage to protect the people who can’t get the vaccine or who have never had the disease from getting infected. Some of the estimates for herd immunity for this infection I’ve seen as low as 70%, which I think is probably too low, and as high as 90% depending on the variants that are currently circulating.”
— Dr. Debra Powell, chief of the division of infectious disease and medical director of infection prevention at Reading Hospital-based Tower Health
the community.
One doctor believes herd immunity will be reached sooner rather than later. In a February Wall Street Journal commentary, Dr. Marty Makary, a professor at Johns Hopkins School of Medicine and Bloomberg School of Public Health, wrote that he expects COVID to be mostly gone by April.
Makary’s prediction is due to the percentage of Americans he believes have natural immunity to COVID-19 due to a prior infection in addition to the percentage of people expected to be vaccinated by the end of March.
A third vaccine and its distribution might hasten the arrival of herd immunity. Its arrival might be only days away.
According to Makary, natural immunity is more common than can be measured through testing. Based on his calculations of the likely number of people who have already been infected with COVID, he believes about 55% of Americans have natural immunity.
“I don’t agree with that,” Powell said of Makary’s April prediction. “I think he’s overestimating the number of the population that has had the infection. I think that’s the flaw in his argument.”
If Powell had to predict when herd immunity might occur, she said it would probably take at least another three months, possibly by midsummer.
‘Beginning of the end’
Another national expert on infectious diseases believes April’s a bit optimistic but also said it’s best for experts to underpromise and overdeliver.
Dr. William Schaffner, professor of infectious diseases at the Vanderbilt University Medical Center, Nashville, Tenn., is cautiously optimistic about herd immunity because of significant declines in new cases, hospitalizations and deaths in a society that now includes more mobility and travel.
“We might be getting some herd immunity in some populations (now) and if you add to that vaccinations, those explanations are the best (for the declines),” he told the Reading Eagle. “They suggest that we may be at the beginning of the end. The question is how soon will we get there?
“We wish for it to be as soon as April, but we haven’t done large scale studies of populations in the United States.”
He expects normalization by late summer in time for the next school year.
“If things happen faster than that, I would be delighted,” he said. “It’s not all smooth downhill skiing.”
Schaffner said many more people have had COVID than the number of cases show, from a majority of people in densely populated areas to roughly 20% to 25% in lightly populated areas.
Many have had the disease and didn’t know it, he said.
In Berks, the number of cases on the books is nearing the 36,000 mark, but the total could be three times that, according to Schaffner’s thinking about the number of people who show no symptoms and victims who assumed they had COVID but never got tested.
Even that 36,000 number that the state Department of Heath reports isn’t completely accurate. About 17% of Berks cases are considered “probable” because they came through antigen and antibody tests, not the PCR test, which involves a nasal swab.
Schaffner said the COVID variants might pose a problem, and another issue would be if vaccinations stall.
“For the moment, the early accepters have been vaccinated and convinced,” he said.
In Berks and Pennsylvania there are many more people who want a vaccine than can get it. Each announcement of some other provider opening shots to the public brings relief to those who get appointments and frustration to more who cannot.
The professor said it would be ideal if 80% of the population were vaccinated, but if it stalls at 65% “there might be opportunities for this virus to continue to spread.”
Then there is also the question of vaccinations in urban cores with overwhelmingly minority populations, where there has been distrust in the process.
Schaffner said the questions are: Can we get the vaccine there, and will the people accept it?
Keep up defenses
Powell noted the best way to achieve herd immunity is through the vaccine rather than relying on the natural process and natural immunity. The coronavirus that caused COVID-19 is still relatively new. Studies have shown the antibodies from a prior infection may last for months, but it is still unclear exactly how long, Powell said.
People can become infected with COVID a second time.
“It is possible,” Powell said. “It is a lower rate of infection that we’re seeing in people who had it one time. But, we have new strains that are circulating. This virus is going to continue to mutate. We will have new variants next month and which variants are going to be predominant in the next six weeks is not known.”
Powell said the current vaccines have shown to be effective against the new strains of the virus.
“The more people who get vaccinated, we can get to herd immunity and stop these variants from emerging,” Powell said. “Reaching that herd immunity as soon as we can, I think, is the best way for us to control this pandemic.”
The end of the pandemic will come once we have reached herd immunity and the virus will no longer be actively circulating in the community.
“It’s herd immunity and then the prevalence of the virus in the community declining,” Powell said. “Herd immunity prevents (the virus) from spreading and then we should see the numbers really, really decrease down to very minimal. That’s the time that we take off our masks.”
While Makary pointed to natural immunity as a reason for the decline in COVID-19 numbers, Powell said there are more causes, most notably vaccinations and safety measures such as mask-wearing and social distancing.
“The message to the population should be that we are working on obtaining herd immunity by vaccination and from people who have already been infected,” Powell said. “But, we can’t let down our guard. We still have to wear our mask, socially distance, wash our hands and I need to encourage people to get the vaccine. I don’t want people to not get the vaccine because they think we’re done with all of this.”
“We might be getting some herd immunity in some populations (now) and if you add to that vaccinations, those explanations are the best (for the declines). They suggest that we may be at the beginning of the end. The question is how soon will we get there?”
— Dr. William Schaffner, professor of infectious diseases at the Vanderbilt University Medical Center