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By Deena Beasley

(Reuters) – As scientists question whether the presence, or absence, of antibodies to the novel coronavirus can reliably determine immunity, some are looking to a different component of the immune system, known as T cells, for their role in protecting people in the pandemic.

Recent studies show that some recovered patients who tested negative for coronavirus antibodies did develop T cells in response to their COVID-19 infection. While the studies are small and have yet to be reviewed by outside experts, some scientists now say that people who experience a mild illness, or no symptoms at all, from the new coronavirus, may be eliminating the infection through this T cell response.

The findings add to the evidence that an effective COVID-19 vaccine will need to prompt T cells to work in addition to producing antibodies, and may have implications for several treatments in development. They may also shed light on how immunity to new exposure to infection could work.

“There is mounting evidence that people exposed to the virus have a transient (short-lived) antibody response, or have a T cell response in spite of a minor or absent antibody response,” Dr Alessandro Sette, professor and member of the La Jolla Institute’s Infectious Disease and Vaccine Center in California, told Reuters.

When a virus gets past the body’s initial defenses – which include infection-fighting white blood cells – a more specific “adaptive” response kicks in, triggering production of cells that target the invader. These include antibodies that can recognize a virus and lock onto it, preventing its entry into a person’s cells, as well as T cells that can kill both invaders and the cells they have infected.

Six months into a global COVID-19 pandemic that has infected more than 12 million people, questions remain about whether the antibody response to this virus is robust and lasts over time. That could mean T cells have a more important role in offering protection against the illness.

“T cells are often important in controlling viral infections. We are seeing evidence of that,” John Wherry, director of the University of Pennsylvania’s Institute for Immunology, told Reuters.

A recent small French study https://www.medrxiv.org/content/10.1101/2020.06.21.20132449v1, not yet reviewed by experts, found that six out of eight family members in close contact with relatives who had COVID-19 developed a T cell response, but did not test positive for antibodies.

A Swedish study https://www.biorxiv.org/content/10.1101/2020.06.29.174888v1.full.pdf of 200 people found a strong T cell response in most individuals who had mild illness or no symptoms following coronavirus infection, regardless of whether they showed an antibody response. The finding suggests that coronavirus infection rates may be higher than what has been studied using antibody tests alone, the researchers said.

MEMORIES OF CORONAVIRUS

The focus on T cell responses could also shed light on the prospect for longer-term immunity.

There is some evidence that T cells developed after exposure to other coronaviruses that cause the common cold could help fight off the new virus, known as SARS-CoV-2.

A study led by the La Jolla Institute detected T cells that reacted to SARS-CoV-2 in about half of stored blood samples collected between 2015 and 2018, suggesting that the immune system cells developed after previous infection with circulating common cold coronaviruses, and that they might help protect against the new virus.

“It is a potentially encouraging piece of evidence,” Wherry said.

Vaccine candidates against COVID-19 currently in the works aim to generate antibody and T cell responses, and the recent findings highlight the importance of gauging the T cell response seen in human clinical trials.

“We believe that the optimal vaccine design would be one that induces both an antibody and T cell response,” Sette said.

After an infection or vaccination, the immune system retains a number of “memory” cells that are already primed to quickly attack the same virus in case of a future infection.

Many countries are using blood tests that look for antibodies to estimate how many people have been infected with the new virus even if they never showed symptoms. But scientists still do not know how antibody levels correlate to exposure to the virus or how long they may last. There are also questions about exactly which combination of immune-system cells will result in significant protection.

Measuring the level of memory T cells is much more complicated, especially if the cells are in lymph nodes or other hard-to-access areas of the body. In addition, T-cell responses are highly variable.

“It is a lot easier to collect antibody data,” said Dr Daniela Weiskopf, an assistant professor at the La Jolla Institute.

(Reporting by Deena Beasley in Los Angeles; Editing by Michele Gershberg and Matthew Lewis)

President Donald Trump answers questions during a coronavirus task force briefing in April. | Win McNamee/Getty Images

President Donald Trump and Republican governors are pointing to fewer coronavirus deaths to suggest that the worst of the coronavirus pandemic has passed — and to blunt criticism that a surge of new infections in more than half the states is proof the country reopened too soon.

But that’s a dangerous gamble. Death rates tell nothing about the current spread of the virus and only offer a snapshot of where the country was roughly three weeks ago. If the caseloads in states like Texas, Arizona and Florida are any indication, the U.S. will almost certainly see a spike in deaths in July that could undermine the entire nationwide reopening effort.

“If you’re going to do that with the death rate, you should be prepared to look at the death rate in a month or so,” said William Hanage, an epidemiologist at Harvard’s school of public health. “You might not find it so attractive.”

Trump on Thursday tweeted the number of infections is going up because of “great testing while the number of deaths (mortality rate) goes way down.”

The nationwide death rate over the last two weeks is about 2.6 percent of all known cases, or roughly half of what it was since the pandemic began.

But public health officials say Trump’s logic is backwards and could give people a false sense of security. The very testing the president blames for increasing case numbers is keeping the death rate low, particularly by identifying younger people who are more likely to be out and could unknowingly be spreading disease.

The mortality rate is declining, in fact, because more vulnerable, mostly older Americans are still sheltering in place, or at least much less likely to be venturing out to newly opened bars and restaurants. In Arizona, for example, people under 44, now make up 60 percent of cases, up from around 40 percent in mid-April, according to the state’s coronavirus dashboard.

“There’s been a large increase in the 20 to 44 [year old] age bracket,“ Gov. Doug Ducey said Thursday.

In Florida, the median age for all new infections this past week was 34, down from about two years from the week before and down significantly since the pandemic began, the state health department reported.

But that doesn’t mean the virus is less deadly or contagious: As infections soar, especially in states like Florida and Arizona that have older populations, the risk of catastrophe grows.

Most important, death follows weeks of illness in most coronavirus cases, which is why experts expect the death toll to rise sharply in the coming weeks.

“The deaths that get reported today are people who got infected three weeks ago,” said Robert Amler, a former HHS regional health administrator.

Some GOP governors are starting to make their own calculations, heeding calls from local health systems worried about having enough beds to treat a surge of patients.

Texas Gov. Greg Abbott on Thursday paused his state’s reopening plan as hospitals in Houston and other locales scrambled to free up ICU beds. Abbott, who led one of the nation’s most aggressive reopenings, is now urging people to stay home as his state contends with more than 5,000 new daily infections. The number of hospitalizations there has doubled in the last 10 days, according to the state health department. Abbott also issued an executive order suspending elective surgeries in some counties seeing the sharpest spikes in cases.

Ducey on Thursday said the rate of spread in his state is “unacceptable” and paused further reopening.

“We expect our numbers to be worse next week and the week following,” Ducey said. “There is no consideration of increasing activity. Arizona is on pause.”

In deep red Utah, Gov. Gary Herbert announced Wednesday that he would not consider lifting more lockdown restrictions for at least two weeks.

“All Utahns should be concerned about the increasing infection rates,” Herbert said. “They should be concerned because of what it does to our hospital capacity.”

Herbert warned packed hospitals can quickly overwhelm health workers. “We have a limitation more on personnel than on bed space,” he said.

Louisiana’s Democratic governor, John Bel Edwards, is keeping occupancy limits in public spaces in place for at least another month, because the average number of new daily infections is up about 50 percent this month and hospitalizations are rising across several parts of his state.

“We simply are not ready to move to the next phase, and ease restrictions further as businesses open widely,” he said, adding that 90 percent of new cases are from community spread, not from congregate settings such as nursing homes or jails.

But other governors have maintained a focus on the mortality rate to justify forging ahead, even as infections spike.

“The most important data is the death rate,” said Tennessee Republican Gov. Bill Lee on Tuesday, after boasting that his state is tops when it comes to hotel and restaurant recovery.

It’s not the first time lawmakers have shifted rationales to justify their actions. When lockdowns were first lifted in early May, some governors who ignored the White House’s criteria for safely reopening pointed to declining cases in their states. When new infections started rising, they said it was safe to proceed because hospitals had plenty of room to treat patients.

The shift to the death rate most alarms public health officials who fear it is distracting the public from taking necessary precautions and allowing elected officials to punt on tough decisions.

“They are grasping at straws to try and explain this away,” said Jeffrey Shaman, an infectious disease researcher at the Columbia University School of Public Health. “We’re looking at people picking at the margins for explanations to deny that we are seeing a surge.”

The Trump administration always expected cases to rise as testing improved and economic activity resumed, and gambled that Americans would trade a certain number of deaths if it meant getting back to work. Trump touted higher stock prices and a better than expected jobs report while 20,000 new infections a day became commonplace.

But the new threat in places like Arizona and Texas has changed the calculus, said Catherine Lutz, an anthropology professor at Brown University.

“The stress on the health care system has de-normalized it again,” she said. “I don’t know if [governors] would have tapped the brakes if we’d been able to handle it in our health care system.”

The exponential spread in the virus, particularly across the Sun Belt, has also scrambled perceptions about what the nation is prepared to accept.

“It doesn’t have to be a huge number for people to say this isn’t right,” Lutz said. “People interpret the number is too much if there is something that can be done to prevent it.”