For all the fear that the coronavirus has caused, one question that has caused fresh alarm is whether it’s possible to get Covid-19 more than once.
In countries including the United States, India, Israel, Iran and Bolivia, there have been reports of coronavirus reinfections — people who test positive for Covid-19, recover and test negative, then months later reportedly test positive again.
There is still much that is not understood about immunity to the novel coronavirus, and reinfections have not been studied much, which makes it challenging to definitively address the possibility of reinfection with Covid-19, experts say.
“Nobody really knows yet. So far there have only been individual reports,” said Brian DeHaven, assistant professor of biology at La Salle University.
Among the explanations for why some may test positive months after recovery: Some people with Covid-19, dubbed “long haulers” may suffer from long, persistent infections and symptoms. For other cases, the tests may not always be accurate.
“Based on what we know from other viruses, it’s possible these reports are misleading test results,” DeHaven said.
Viruses have a “limit of detection” — thresholds at which the amount of a virus can be detected. For instance, a negative coronavirus test result doesn’t necessarily mean no infection. Rather, it suggests there is no detectable infection, and it’s possible for levels of infection to hover around the limit and be detectable, non-detectable, and then detectable again in the same person.
In Korea, it’s been suggested that some false-positive test results may be caused by material from dead viruses — as fragments of these dead cells require a longer time to be cleared from the body.
Some viruses, such as herpes, can also be latent — which means they stay dormant within cells, and reactivate later, causing disease. There is currently no evidence to suggest this might be the case for Covid-19.
What has fuelled some of the alarm surrounding reinfections concerns antibodies — specific molecules naturally produced by the body’s immune system following infections to protect against re-infections. Several recently published studies suggest that antibodies to Covid-19 decline substantially within months after infections, which might bolster the possibility of reinfection.
These findings may not be as discouraging as they’ve been made out to be.
“One big caveat is whether antibodies are the full story in protecting against Covid-19,” said Otto Yang, professor of medicine and infectious diseases at University of California, Los Angeles. “Another caveat is whether the antibody testing we are doing reflects those (antibodies) that are useful for protection.”
Antibodies may be a good marker of immunity, but it’s not always the case, and they’re expected to decline over time.
“After all infections, your antibody levels go down,” DeHaven said. “You would expect that to happen. For coronaviruses in general, the (antibody) levels go down relatively quickly for reasons we don’t understand very well.”
Still, experts offer hope against coronavirus re-infections: antibodies are not the only tool the body uses to protect itself.
“Protection against an infection is mediated by other arms of the immune system,” Yang said.
One such arm is T cells, which among many functions, directly kill infected cells in the body.
“T-cell responses tend to be very involved in controlling the severity of infections in general,” Yang said. “It’s possible that if someone gets reinfected with Covid-19, any reinfection could be much milder than the first.”
In one study of a different coronavirus published in 1990, antibodies in volunteers who had been infected with the virus declined over a year. When the volunteers were re-infected with the same virus, they all developed some symptoms, but the infection was less severe. For the novel coronavirus, studies in monkeys have also shown that there is protection from reinfections up to 28 days after the first infection.
Yang added that so far, the reports of people getting reinfected aren’t well-documented and verified.
Even if immunity to the novel coronavirus doesn’t last for years, it doesn’t spell the end of hope for immunity.
“That’s why some vaccines have to be given as boosters,” Yang said. “People with severe disease may have much higher levels of antibodies that last longer. Maybe immunity is a dose-related thing and a vaccine can compensate from that. It’s an open question right now.” 
— The Philadelphia Inquirer/TNS


Public health experts fear hasty FDA signoff over possible vaccine 


The vaccine trial that Vice President Mike Pence kicked off in Miami last Monday gives the United States the tiniest chance of being ready to vaccinate millions of Americans just before Election Day.
It’s a possibility that fills many public health experts with dread.
Among their concerns: Early evidence that any vaccine works would lead to political pressure from the administration for emergency approval by the Food and Drug Administration. That conflict between science and politics might cause some people to not trust the vaccine and refuse to take it, which would undermine the global campaign to stop the pandemic. Or it could lead to a product that is not fully protective. Confidence in routine childhood vaccinations, already shaken, could decline further.
“The fear is that you wind up doing to a vaccine what (Trump has) already done with (opening) school,” said Dr Joshua Sharfstein, a former FDA deputy commissioner and a professor at Johns Hopkins University in Baltimore. “Take an important, difficult question and politicise it. That’s what you want to avoid.”
Last Monday at 6:45am, the first volunteer in the landmark phase 3 trial for the Moderna Therapeutics vaccine received a shot at a clinic in Savannah, Georgia. Clinicians at 88 other sites, stretching from Miami to Seattle, were also preparing to deliver the experimental shot in a trial that aims to enrol 30,000 people.
Dr Anthony Fauci, the country’s leading infectious disease expert, told reporters he hoped 15,000 could be vaccinated by the end of the week, although he provided no information about progress toward that goal. All volunteers would receive a second shot 29 days after their first inoculation. (Half will receive a placebo containing saline solution.)
Another vaccine, produced by Pfizer with the German company BioNTech, also entered a large phase 3 US trial this week. It’s being tested independently of the National Institutes of Health, which is partially funding the Moderna trial as well as tests for an Oxford University/AstraZeneca vaccine trial, and others in the future. AstraZeneca has said some doses of its vaccine might be ready as early as September.
Fauci said he expects the Moderna trial to provide an answer about whether that vaccine works by the end of the year — and it’s “conceivable” an answer could come in October. “I doubt that, but we are leaving an open mind that it is a possibility.”
Such a fast pace worries some experts.
“I don’t see how that’s remotely possible unless the thing I most fear happens, a truncated phase 3 trial with just an idea of efficacy, an idea of common side effects, and then it rolls out,” said Dr Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia.
Pence downplayed such fears, telling reporters: “There will be no shortcuts. There will be no cutting corners.”
Officials are pressing for an open and transparent process.
Rep. Raja Krishnamoorthi, D-Illinois, chairman of the House Oversight and Reform Subcommittee on Economic and Consumer Policy, is preparing to release a bill requiring the FDA to have an expert panel review any Covid-19 vaccine and issue a recommendation before FDA Commissioner Stephen Hahn makes a decision.
With past vaccines, the FDA has generally relied on such a committee, made up mostly of vaccine experts and appointed by the FDA commissioner. They typically conduct a painstaking examination of all evidence before voting on whether the FDA should approve a vaccine. The commissioner has rarely, if ever, gone against the committee’s decisions.
Hahn undercut confidence in the FDA’s independence earlier in the year, many observers felt, when he issued an Emergency Authorization Use declaration for hydroxychloroquine, a drug used to treat malaria that President Donald Trump and members of his administration have continued to tout, erroneously, as a cure for Covid-19. 
The FDA later revoked the authorisation, which was made without consulting an independent committee.
“FDA’s independence has been threatened, no question, by the hydroxychloroquine issue,” said Dr Jesse Goodman, a Georgetown University professor who led the FDA’s biologics division and later was chief scientific officer.
The agency must give outside scientists and the public the opportunity to see the data and the FDA’s reasoning before coming to such a decision, he said. 
                     — Kaiser Health News