The Plain community in Lancaster County has become the 'first to achieve her immunity,' according to a local administrator of a medical center in the area

Allen Hoover of the Parochial Medical Center said that 90% of households became infected with virus when they resumed church services late last spring

As Hoover observed, faith in herd immunity prompted members of community to relax on key mitigation efforts such as masking and social distancing

It's unknown whether achieving herd immunity in 2020 would be beneficial now

'It really went through pretty quick, in a few weeks,' Cooper said.

The number of patients ebbed in the summer before picking up again in the fall, although not at nearly the rate as was seen in the spring.

Cases now are rare. Hoover said Tuesday that the center hasn't had a patient present with COVID-19 symptoms in roughly six weeks.

'You'd actually have to test the herd'

Epidemiologists from the University of Pittsburgh, Washington State, Johns Hopkins, Emory and the University of California all said a widespread outbreak leading to herd immunity in the Plain community would be rare, but possible.

'It's extremely unusual,' Lofgren, at Washington State University, said of herd immunity to COVID-19. 'It would be the first general population in the United States that's done it.'

Significant outbreaks have been identified elsewhere.

The CDC, for example, studied COVID-19 outbreaks among smaller Amish communities in rural Ohio and Indiana.

As the CDC has noted, the Amish emphasis on strong social bonds and religious gatherings posed a unique public health challenge during the pandemic.

Unlike the outbreak Hoover described in Lancaster County, however, the Ohio and Indiana communities conducted testing.

'They really contributed to a lot of spread of COVID in the community,' said Shirley Bixby, director of nursing for the Ashland County Board of Health in northeastern Ohio. 'It was quite nerve-wracking.'

In Indiana, COVID-19 infections were so common among the Amish that residents believe most had been exposed.

At the height of the summer outbreak, seven out of 10 COVID-19 tests came back positive, said Dr. Daniel N. Kragt, a physician at Dayspring Christian Health Care in Middlebury, Indiana.

Dayspring is a cash-only provider in the middle of the Amish community, about 35 miles east of South Bend.

For all the tests Kragt conducted, about 40% of Amish patients declined.

Making scientific conclusions about immunity is difficult, Kragt noted, because very often 'the herd doesn't want' to be tested.

'To say you have herd immunity, you'd actually have to test the herd,' Kragt said.

'Plenty' of death certificates

COVID-19 has been devastating to Pennsylvania seniors, with nine out of every 10 fatalities among those 60 and older. In Lancaster County, 96% of COVID-19 fatalities as of March 17 — 926 of 968 — have been people age 60 or older.

The same appears to be true for the elderly in the Plain community, as Hoover estimated most deaths were 70 and older.

Cooper said she signed 'plenty' of death certificates during that time.

But the death toll may never be known.

Lancaster County Coroner Dr. Stephen Diamantoni identified fewer than a dozen deaths in the Plain community, an estimate he derived at by using decedent location and last name.

Virus-related deaths, Cooper speculated, were likely listed as pneumonia.

Diamantoni does not dispute this.

People have to die from something,' Diamantoni said. 'If they don't want any intervention done, these people could slip under the radar.'

Even if more virus testing had been done, it's unlikely the public would know much more about the disease's impact. That's because demographic information collected by health departments — such as race and ethnicity — does not include religion.

The fatalities have not gone unnoticed.

A contributor to The Diary, a monthly newspaper published in Kirkwood with Amish reports on crops, births, deaths, weddings and ordinations across the United States, tallied the annual number of obituaries since 2015.

'As you can see, the number of deaths this year is 100 count higher than any of the five previous years,' Joas D. Troyer, of Hestand, Kentucky, wrote in January's edition. 'This may give us a good idea how many people died from coronavirus.'

Herd immunity — either through infection or vaccination — has been touted as the way back to normal.

'The only true herd immunity that we can bring as a community is for people to be vaccinated,' said Alice Yoder, executive director of Community Health at Penn Medicine Lancaster General Health.

Because immunologists don't yet know what the threshold is for COVID-19 immunity, Dr Anthony Fauci, the nation's top infectious disease expert, has said the coronavirus could require vaccination rates as high as 90%.

'The key is that there is not necessarily a magic number,' said Dowdy, at Johns Hopkins Bloomberg School of Public Health.

The lack of infection data on the notoriously private Plain community makes proving or disproving whether Anabaptists (a Christian community of which Amish and Mennonites are a part) achieved herd immunity impossible 11 months later. Testing could be conducted now, but the absence of antibodies — Dowdy and other experts said — doesn't mean the lack of infection.

As the United States races to stay ahead of virus mutations, the more pressing issue — these experts said — was vaccine hesitancy. As of March 16, there were two other mutations in Pennsylvania: 68 cases of the UK variant and one South African case, according to the CDC.

'The higher the vaccination in the (Plain) community, the better it will be for the entire community,' said Dr Amesh Adalja, an infectious diseases physician and senior scholar at the Johns Hopkins Center for Health Security.

Despite lower childhood vaccination rates among the Amish, there is no religious prohibition, said Nolt, at Elizabethtown College, who has written 14 books about the Amish.

In a 2017 doctoral study that examined Amish perceptions in Lancaster County, Cooper found the majority had a positive attitude toward immunizations and roughly six in 10 surveyed were likely to vaccinate their children.

As Cooper noted in her study, three out four of those she surveyed said they had never discussed vaccination with their health care provider.

'Providers are missing many opportunities to discuss vaccines with Amish parents,' wrote Cooper, at the Parochial Medical Center.

Vaccine efforts among the Plain community could prove challenging.

'I think it will be a very hard sell,' Hoover said.

The Amish have been persuaded to embrace mass vaccination efforts before, most notably after a polio outbreak in 1979 and a rash of measles in 1991. This has left health officials hopeful the Anabaptists will respond again.

The Pennsylvania Amish Safety Committee and other partnerships will be crucial to outreach efforts that have already begun. Comprised of five elected Old Order Amish men, the committee provides safety information and has helped spearhead issues such as the 2011 effort to cover holes in haylofts after emergency room doctors encountered a number of Plain sect children who had fallen through.

The goal, Lancaster General's Yoder said, is to achieve a vaccination rate protective of the entire community.

'Of course,' Yoder said, 'there might be some concern that we don't reach that.'

The way Dr Holmes Morton sees it, these religious sects must take responsibility for getting vaccinated to protect their Lancaster County neighbors.

'I just think the Plain community has to get involved in a public-health sense,' said Morton, founder of the Central Pennsylvania Clinic in Belleville, Mifflin County.

Morton, who first created the Clinic for Special Children in Strasburg, is renowned for his pioneering work on genetic diseases among Plain children.

'Just because you're Plain doesn't mean you're exempt,' Morton said. 'God helps those who help themselves.'

The Plain community includes Amish and Old Order Mennonites.

With a population of 40,525 people, the Lancaster Amish settlement is the largest in the United States and extends into Chester County and northern Maryland.

Roughly 88 per cent, or more than 35,000 adults and children in this settlement, live within the borders of Lancaster County.

Old Order Mennonites primarily consist of three groups — the Groffdale Mennonite Conference, the Stauffer Mennonite Church and Reidenbach Mennonites — with a combined population of about 5,700.

Together, these religious sects represent nearly 8 per cent of the 545,000 people living in Lancaster County.

Herd immunity occurs when a sufficient number of people have immunity to a disease to prevent a virus from finding new hosts, thereby protecting the wider population. Immunity can be achieved either through recovering from an infection or vaccination.

Herd immunity is the only way to eradicate COVID-19.

The more transmissible a disease, the higher the percentage of a population needs to be immune. Initially, scientists estimated 60% to 70% of the population needed to acquire resistance to provide herd immunity.

It's difficult to know the precise threshold for the novel coronavirus.

Fauci late last year began moving the goal post, adjusting that estimate up to as high as 90 per cent.

Viruses constantly mutate and COVID-19 is becoming more transmissible.

Because the elderly and other individuals with compromised immune systems cannot risk a COVID-19 infection, herd immunity will be crucial to protecting these groups.