Friday Update for 2021-02-12: Antiviral
Herewith three items of pandemic news you may have missed recently: A promising antiviral; a rare blood disorder perhaps related to vaccination; and the prospects for children getting vaccinated. Plus news briefs and a frippery.
When will kids get vaccinated?
The urgency to vaccinate children is plain enough. Besides increasing the safety of everyone involved in a return to in-person classes, vaccination would shrink a potential reservoir of the SARS-CoV-2 virus in which it can continue to mutate and spread.
Dr. Anthony Fauci said that vaccines may be approved by September for children as young as 6. But others interviewed by ProPublica believe that manufacturers are not moving fast enough with clinical trials for that to happen.
The way age de-escalation normally works in such trials, according to Fauci, is that vaccines are tested for safety and efficacy in (for example) people aged 12 to 16; then 9 to 12; then 6 to 9.
Pfizer is the only vaccine maker with studies in a young population that are far enough along to promise results by summer’s end. They have fully enrolled (n = 2,259) a trial for kids 12 to 15, and plan to start another for those 5-11 when the first one reads out.
Johnson & Johnson, whose vaccine candidate is being examined by the FDA for an emergency use authorization, has not yet begun any studies in younger cohorts.
Testing in younger people will have some differences from the large-scale Phase III trials the manufacturers have mounted in adults. They will be smaller, around 3,000 participants; doses will be smaller; and the researchers will be looking for different signals of both safety and efficacy. One adverse event they will be watching for is any sign of immune disorders, such as MIS-C, that may be related to vaccination. For efficacy, researchers won’t be looking for symptomatic Covid-19, which is rarer in children who get infected; rather they will be measuring antibody responses, even though no correlates of protection have been nailed down for this disease.
Read ProPublica’s extensive article, and the coverage at MPR News, for more detail on the planning for vaccine testing in children.
One-in-a-million blood disorder
By now most of us have heard about the rare instances of anaphylaxis following injection with either Moderna’s or Pfizer’s vaccine — fewer than one in 100,000 people have experienced this. An even rarer possible side effect of vaccination is now showing up: 36 people, out of 31 million vaccinated, have suffered the onset of a rare blood disorder called immune thrombocytopenia, in which the immune system destroys blood platelets. The reasons for its onset are unknown.
It is not certain that these incidents are related to the vaccine. Officials at the FDA and the CDC are looking into the reports. So far the condition is appearing at a rate roughly consistent with its incidence in the US population.The NY Times article linked above quotes two hematologists who believe that at least some of the reported cases of immune thrombocytopenia were probably brought on by the Covid-19 vaccines. The condition afflicts about 50,000 people in the US, and is sometimes triggered after a viral infection. It is generally treatable.
The risks of Covid-19 far outweigh the chances of running afoul of this blood disorder. The advice for people who have already experienced immune thrombocytopenia: talk it over with your hematologist, but getting vaccinated if you have the opportunity is probably your best bet.
A promising antiviral
Vincent Racaniello, host of This Week in Virology, has a post on his virology blog profiling an orally available antiviral called EIDD-2801 (also known as Molnupiravir). It has shown great promise in testing in ferrets and mice, for both prophylaxis and treatment.Specially engineered mice were infected with SARS-CoV-2 and then treated orally with EIDD-2801 at 24 and 48 hours following infection, then every 12 hours. For the mice first treated at 48 hours, viral load dropped 96%. For those dosed at 24 hours post-infection, the virus titer was reduced by a factor of 25,000. In a separate experiment where the first dose of EIDD-2801 was administered 12 hours before infection, viral load was reduced by 100,000 times. (On a human RT-PCR test for Covid-19, such a reduction would bump the Ct value by 16.6.)
Phase II and III human trials are underway now. Racaniello concludes, “One wonders how the trajectory of the COVID-19 pandemic might have been altered had EIDD-2801 been ready for efficacy trials against SARS-CoV-2 in early 2020.”
- Half of transmission comes from those without symptoms — The U of MN’s Center for Infectious Disease Research and Policy has a summary of research published in PNAS concluding that asymptomatic and pre-symptomatic carriers of SARS-CoV-2 are responsible for at least half of the virus’s spread. The consensus before this work pinned down the number was more like 40%.
- CDC says the vaccinated need not quarantine — New guidance from the Centers for Disease Control and Prevention gives a pass from quarantining to anyone two weeks past their second shot. It is not certain that the vaccinated cannot become infected and transmit disease, but the CDC judges that the risk is reduced enough that it is outweighed by the value of avoiding unneeded quarantines. Here is a summary from CNN.
- No vaccination card selfies please — You are excited to be fully vaccinated, finally. You’re tempted to take a selfie with your vaccination card and post it jubilantly to all your social media. Security experts say: Don’t do that.
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