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.
More than 125 children and adults who attended a religious camp in Texas last month have now tested positive for Covid-19, camp officials said this week in a statement that also warned that many more people may have been exposed to the coronavirus.
In addition to the 125 people who tested positive, “hundreds more were exposed to Covid-19 at camp,” Bruce Wesley, senior pastor for Clear Creek Community Church, wrote on the church’s website. The church is in League City, about 30 miles southeast of Houston. “And hundreds of others were likely exposed when infected people returned home from camp.”
As of early May, masks were “optional in all areas,” according to the camp’s website. Telephone and email messages sent to the camp on Tuesday evening were not immediately returned.
“From the beginning of the pandemic, we have sought to love our neighbors by practicing strict safety protocols,” Mr. Wesley said in the statement. “We are surprised and saddened by this turn of events. Our hearts break for those infected with the virus.”
More than 400 people participated in the student ministry camp, according to the statement. The camp also said it had consulted with the Galveston County Health District and canceled services for now, but will resume activities on Sunday.
In a statement on Tuesday, Galveston health officials said the Delta variant of the virus had been detected in three test samples linked to “a church camp.” Dr. Philip Keiser, interim head of the Galveston County Local Health Authority, said, “In this outbreak, at least as of now, it appears most of the people who have tested positive are old enough to be vaccinated.” The camp served children in grades six through 12, it said.
News of the outbreak in Texas comes during the return of the traditional summer camp season, when day and sleep-away camps are about to welcome children who just completed a school year dramatically altered by Covid-19 health restrictions, and many children are looking for relief from the soaring summer temperatures.
In Illinois, 85 teenagers and adults tested positive for Covid-19 after attending a camp that did not check the vaccination records of participants or require masks indoors, the Illinois Department of Public Health said last month. At least 25 workers at a Christian summer camp in Oklahoma tested positive for Covid-19 in June, Public Radio Tulsa reported.
Officials across the country have rolled back face-covering and social distancing rules that were put in place more than a year ago, even as new variants of the virus have quickly spread in areas with low vaccination rates. In Galveston, 44 percent of residents have been vaccinated, slightly above the statewide vaccination rate of 41 percent.
In guidance for people attending or operating youth camps, the Centers for Disease Control said in late May that “everyone” aged 12 or older should get vaccinated and that camps “should be supportive of campers or staff who choose to wear a mask.”
Fiji, which got through the first year of the pandemic almost untouched, is now battling one of the fastest-growing Covid-19 outbreaks in the world.
The number of new coronavirus cases reported daily in the Pacific island nation of 900,000 people has soared into the hundreds over the past month, after never exceeding single digits before late May.
The surge is swamping the country’s ability to cope. Fiji’s largest hospital is now exclusively treating Covid-19 patients, and its mortuary is filled to capacity, the health ministry said on Monday. More than 1,000 Covid patients have been sent home from medical facilities to isolate themselves because the facilities had no space. The government is working to turn a sports arena outside Suva, the capital, into a makeshift clinic.
The country, which is using the AstraZeneca vaccine, depends on Australia and New Zealand to supply it with doses, but New Zealand’s medical regulatory body has not yet authorized the AstraZeneca vaccine, complicating the rollout. About 31 percent of Fijians have had at least one dose of a coronavirus vaccine, but fewer than 5 percent are fully vaccinated, according to a New York Times database.
Instead, New Zealand has provided the country with 40 million New Zealand dollars, or $28 million, worth of aid and support. “We have provided support in the form of PPE and of course the commitment we’ve made around AstraZeneca vaccines, which is what Fiji are using for their roll-out,” Prime Minister Jacinda Ardern said.
James Fong, Fiji’s health secretary, said that some in the country were putting off seeking treatment for Covid symptoms, sometimes with deadly results.
“We are also sadly seeing people with severe disease die at home, or on the way to hospital, before our medical teams have a chance to administer what could potentially be lifesaving treatment,” Mr. Fong said.
Thirty-seven of the 39 Covid deaths reported in Fiji throughout the pandemic have occurred since the latest outbreak began.
Officials say the outbreak appeared to be driven by one case of the highly contagious Delta variant that escaped the country’s isolation facilities and spread rapidly in the community.
Repeated breaches of local health restrictions have further increased the spread. More than 1,000 people have been arrested over breaches of a national curfew, and 48 people were arrested in a 24-hour period this week over breaches of mask requirements, according to the police. The government has declined to impose a lockdown to contain the outbreak.