Pfizer reported on Wednesday that the power of its two-dose Covid vaccine wanes slightly over time, but nonetheless offers lasting and robust protection against serious disease. The company suggested that a third shot could improve immunity, but whether boosters will be widely needed is far from settled, the subject of heated debate among scientists.

So far, federal health officials have said boosters for the general population are unnecessary. And experts questioned whether vaccinated people should get more doses when so many people have yet to be immunized at all.

Continue reading “Citing New Data, Pfizer Outlines Case for Booster Shots” →

As Israel struggles with a new surge of coronavirus cases, its health ministry reported on Thursday that although effectiveness of the Pfizer-BioNTech vaccine remains high against severe illness, its protection against infection by the coronavirus may have diminished significantly compared with this winter and early spring.

Analyzing the government’s national health statistics, researchers estimated that the Pfizer shot was just 39 percent effective against preventing infection in the country in late June and early July, compared with 95 percent from January to early April. In both time periods, however, the shot was more than 90 percent effective in preventing severe disease.

Continue reading “Israeli Data Suggests Possible Waning in Effectiveness of Pfizer Vaccine” →

Two decades after the draft sequence of the human genome was unveiled to great fanfare, a team of 99 scientists has finally deciphered the entire thing. They have filled in vast gaps and corrected a long list of errors in previous versions, giving us a new view of our DNA.

The consortium has posted six papers online in recent weeks in which they describe the full genome. These hard-sought data, now under review by scientific journals, will give scientists a deeper understanding of how DNA influences risks of disease, the scientists say, and how cells keep it in neatly organized chromosomes instead of molecular tangles.

Continue reading “Scientists Finish the Human Genome at Last” →

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.