Israel’s nationwide campaign to provide its population with COVID-19 vaccine boosters appears to benefit recipients. A third dose of the Pfizer-BioNTech vaccine significantly lowers the risk of infection, according to two new studies.
A report for the country’s Ministry of Health, posted Friday, showed a third dose reduced recipients’ risk of testing positive for SARS-CoV-2 by more than 10-fold 2 weeks later. And in a preprint posted yesterday, researchers used data from a health maintenance organization (HMO) to calculate that a third dose roughly halves a person’s chances of testing positive for the virus starting 1 week after the shot and further reduces it after the second week.
Israel’s case numbers and hospitalizations continue to climb as the Delta variant spreads. The country recorded 10,947 new cases on Monday, more than on any other day since the start of the pandemic. But the number of cases in older people began to slow in the weeks after 31 July, when third doses of the messenger RNA vaccine were offered to people ages 60 and older—a sign that boosters may be working. On 29 August, Israel announced it would expand the booster program to everyone over the age of 12 whose second dose was at least 5 months earlier. More than 2.1 million people have already received a third dose, the government said yesterday.
That boosters can reduce infections is not a surprise, says David Dowdy, an epidemiologist at Johns Hopkins University. “If your goal is to provide someone with high levels of short-term immunity, there’s no question that a good way to do this is … through a booster shot,” he says. The findings also add to evidence that the current vaccines are still effective against the Delta variant. But Dowdy warns that because the studies only cover a short period after the booster shot, it remains unclear how long the increase in protection will last.
Researchers from Israel’s Ministry of Health and several universities analyzed information about more than 1.1 million Israelis over the age of 60 in the ministry’s database, correlating COVID-19 diagnoses between 30 July and 22 August with whether and when people had received a booster. Twelve days after people received a third dose, they found, the risk of infection was reduced more than 10-fold. That brings protection back up to the 95% range seen shortly after the second dose. The effect against severe disease was even larger, reducing the risk 15 times, but the authors caution that small numbers of patients with severe disease and the study’s short time frame mean the result has a large uncertainty.
The other study comes from researchers at KSM Research and Innovation at Maccabi Healthcare Services (MHS), Israel’s second largest HMO. They teamed up with researchers at Yale School of Public Health to see whether they could tease out an early effect from the booster in health records from MHS’s 2.5 million members, just more than one-quarter of the Israeli population.
The team analyzed results from 182,076 polymerase chain reaction tests performed on 153,753 MHS members over the age of 40 during the first 3 weeks of August, comparing those who tested negative with those who tested positive. Between 7 and 13 days after a booster, a person’s chance of testing positive fell by 48% compared with someone who had received only two doses, the analysis showed; from 14 to 21 days after the shot, the chance fell by 70%. The study did not look at severe disease, only at new infections.
Dowdy says the result are good news, but don’t prove that making boosters widely available is wise. “The question is not, ‘Does a booster shot ramp up your immune system in the short term?’” he says. “But rather ‘Does a booster shot provide a meaningful increase in longer term immunity over months? And if so, what is the right interval for providing booster shots?’” The answers to those crucial questions, he says, are still “completely unknown.”
Yale’s Daniel Weinberger, who helped lead the study, agrees. “Our study looked at a very narrow question,” he says. Short-term protection “is really only one piece of the puzzle.”
If the booster’s additional immunity fades quickly, or if the booster campaign distracts from surveillance efforts or from reaching people who have not been vaccinated at all, Dowdy says, the effort will have little long-term impact: “We need longer term data before we can say that giving people boosters at any given interval is the right strategy.”
Source: Science Mag