In the latest volley of the debate over the origins of the coronavirus, a group of scientists this week presented a review of scientific findings that they argue shows a natural spillover from animal to human is a far more likely cause of the pandemic than a laboratory incident.

Among other things, the scientists point to a recent report showing that markets in Wuhan, China, had sold live animals susceptible to the virus, including palm civets and raccoon dogs, in the two years before the pandemic began. They observed the striking similarity that Covid-19’s emergence had to other viral diseases that arose through natural spillovers, and pointed to a variety of newly discovered viruses in animals that are closely related to the one that caused the new pandemic.

Continue reading “A Group of Scientists Presses a Case Against the Lab Leak Theory of Covid” →

As the Delta variant sweeps the world, researchers are tracking how well vaccines protect against it — and getting different answers.

In Britain, researchers reported in May that two doses of the Pfizer-BioNTech vaccine had an effectiveness of 88 percent protecting against symptomatic disease from Delta. A June study from Scotland concluded that the vaccine was 79 percent effective against the variant. On Saturday, a team of researchers in Canada pegged its effectiveness at 87 percent.

And on Monday, Israel’s Ministry of Health announced that the effectiveness of the Pfizer-BioNTech vaccine was 64 percent against all coronavirus infections, down from about 95 percent in May, before the Delta variant began its climb to near-total dominance in Israel.

Although the range of these numbers may seem confusing, vaccine experts say it should be expected, because it’s hard for a single study to accurately pinpoint the effectiveness of a vaccine.

“We just have to take everything together as little pieces of a puzzle, and not put too much weight on any one number,” said Natalie Dean, a biostatistician at Emory University.

In clinical trials, it’s (relatively) easy to measure how well vaccines work. Researchers randomly assign thousands of volunteers to get either a vaccine or a placebo. If the vaccinated group has a lower risk of getting sick, scientists can be confident that it’s the vaccine that protected them.

But once vaccines hit the real world, it becomes much harder to measure their effectiveness. Scientists can no longer control who receives a vaccine and who does not. If they compare a group of vaccinated people with a group of unvaccinated people, other differences between the groups could influence their risks of getting sick.

It’s possible, for example, that people who choose not to get vaccinated may be more likely to put themselves in situations where they could get exposed to the virus. On the other hand, older people may be more likely to be vaccinated but also have a harder time fending off an aggressive variant. Or an outbreak may hit part of a country where most people are vaccinated, leaving under-vaccinated regions unharmed.

One way to rule out these alternative explanations is to compare each vaccinated person in a study with a counterpart who did not get the vaccine. Researchers often go to great lengths to find an unvaccinated match, looking for people who are of a similar age and health. They can even match people within the same neighborhood.

“It takes a huge effort,” said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Health.

For its new study, Israel’s Ministry of Health did not go to such great lengths to rule out other factors. “I am afraid that the current Israeli MoH analysis cannot be used to safely assess it, one way or another,” Uri Shalit, a senior lecturer at the Technion — Israel Institute of Technology, wrote on Twitter.

Israel’s numbers could also be different because of who is getting tested. Much of the country is vaccinated. During local bursts of new infections, the government requires testing for anyone — symptoms or not — who came into contact with a person diagnosed with Covid-19. In other countries, it’s more common for people to get tested because they’re already feeling sick. This could mean that Israel is spotting more asymptomatic cases in vaccinated people than other places are, bringing their reported effectiveness rate down.

Fortunately, all the studies so far agree that most Covid-19 vaccines are very effective at keeping people out of the hospital and have generally protected against the Delta variant. Israel’s Ministry of Health estimated that the Pfizer-BioNTech vaccine is about 93 percent effective in preventing serious illness and hospitalization.

“Their overall implications are consistent: that protection against severe disease remains very high,” said Naor Bar-Zeev, an associate professor at the Johns Hopkins Bloomberg School of Public Health.

Because effectiveness studies are so tricky, it will take more work to determine how big a threat Delta poses to vaccines. Dr. Lipsitch said that studies from more countries would be required.

“If there are five studies with one outcome and one study with another, I think one can conclude that the five are probably more likely to be correct than the one,” Dr. Lipsitch said.

Copyright 2021 The New York Times Company. Reprinted with permission.

The German company CureVac announced on Wednesday the final results of its late-stage vaccine trial, confirming earlier data showing that its shot is far less protective than other vaccines.

Overall, the CureVac vaccine had an efficacy of just 48 percent against Covid-19. The Moderna and Pfizer-BioNTech vaccines, which use the same mRNA technology as CureVac’s, delivered efficacy rates around 95 percent in clinical trials.

CureVac’s vaccine proved somewhat better for younger volunteers: For those between the ages of 18 and 60, the efficacy rose to 53 percent. In that group, the researchers also found the vaccine provided 100 percent protection against hospitalization and death.

Forty thousand people participated in the company’s trial in Europe and Latin America. By the end of the study, 288 volunteers had gotten Covid-19.

CureVac had to contend with 15 different variants of the coronavirus. Genetic testing showed that only 3 percent of the cases were caused by the original version of the coronavirus. It’s possible that some of the variants were able to evade the immunity provoked by the CureVac vaccine. (No variants had become widespread in 2020 when Moderna and Pfizer-BioNTech ran their trials.)

But vaccine experts have also questioned whether part of CureVac’s problem was with the design of the vaccine itself. The precise recipe that CureVac used to build its vaccine may have blunted its effectiveness.

The European Medicines Agency opened a rolling review of CureVac’s vaccine in February, and the company said it would continue its submission with these data. The vaccine “will be an important contribution to help manage the Covid-19 pandemic and the dynamic variant spread,” Franz-Werner Haas, the chief executive of CureVac, said in the announcement.

Copyright 2021 The New York Times Company. Reprinted with permission.

Three scientific studies released on Monday offered fresh evidence that widely used vaccines will continue to protect people against the coronavirus for long periods, possibly for years, and can be adapted to fortify the immune system still further if needed.

Most people immunized with the mRNA vaccines may not need boosters, one study found, so long as the virus and its variants do not evolve much beyond their current forms — which is not guaranteed. Mix-and-match vaccination shows promise, a second study found, and booster shots of one widely used vaccine, if they are required, greatly enhance immunity, according to a third report.

Continue reading “Three Studies, One Result: Vaccines Point the Way Out of the Pandemic” →

Early results from a British vaccine study suggest that mixing different brands of vaccines can provoke a protective immune response against Covid-19. In the trial, volunteers produced high levels of antibodies and immune cells after getting one dose of the Pfizer-BioNTech vaccine and one dose of the AstraZeneca-Oxford shot.

Administering the vaccines in either order is likely to provide potent protection, Matthew Snape, a vaccine expert at the University of Oxford, said at a news conference on Monday. “Any of these schedules, I think could be argued, would be expected to be effective,” he said.

Continue reading “Mixing Pfizer and AstraZeneca vaccines provides strong protection, according to a preliminary study.” →