Is Israel or UK right about COVID-19 vaccine effectiveness? - The Jerusalem Post

Is the Pfizer coronavirus vaccine 88% or only 39% effective against preventing symptomatic infection?

Two separate studies, one published by the Israeli Health Ministry and the other published in the New England Journal of Medicine late Thursday showed striking differences.

“This discrepancy is kind of unsettling and needs to be further investigated,” said Prof. Cyrille Cohen, a member of the advisory committee for clinical trials on SARS-COV2 vaccines at the Health Ministry.

Specifically, the ministry's study found that the Pfizer coronavirus vaccine was only 40% effective against symptomatic cases of COVID-19 and 39% effective at stopping infection at all against the Delta variant.

It did, however, show that the vaccine remains 91% effective against developing serious cases of the disease and 88% effective against hospitalization. 

The British study, in contrast, found that two doses of the Pfizer vaccine was 88% effective against stopping symptomatic infection against the Delta variant. 

The Delta variant is currently responsible for more than 90% of cases in the country and has been found to be significantly more contagious.

According to Cohen, there are several possible answers to the data gap.

 
FIRST and critical is the difference in time between exposure to the Delta variant and vaccination. 

England vaccinated at a much slower pace than Israel, meaning that the majority of its population was only fully vaccinated by mid-April 2021. This is in contrast to Israel, where around 90% of the country’s most vulnerable population were jabbed by the end of January. 

It is beginning to become clear that vaccine immunity begins to wane after about six months. The Israeli study showed that for people vaccinated more than six months ago, the effectiveness of the vaccine at stopping coronavirus dropped to as low as 16%.

Among more than 1.8 million people who received two shots by January 31, some 5,770 contracted the virus – and 1,181 of them, or 20% of all new infections, were contracted during the week of July 11 to 17, the Health Ministry reported.

“If you take into account that they [the UK population] vaccinated later and were exposed to the Delta variant a month before us,” Cohen said, “it could make sense that at the point they checked, they had around 80% effectiveness. The question is what is going to happen in three months? Will they see the same efficacy that we are seeing?”

THE NEXT issue is age. 

Both Israel and the UK were careful to first vaccinate healthcare workers and the elderly. In England, however, the older population was largely administered the AstraZeneca vaccine, whereas people under 40 were offered Pfizer or Moderna as an alternative due to evidence linking AstraZeneca to rare blood clots. The same study showed that the AstraZeneca vaccine was only 67% effective against symptomatic disease after two doses. 

In Israel, everyone received Pfizer. Breakthrough infections were most prominent among people 60 and older, a cohort that already has a greater tendency to be immunocompromised and prone to developing symptomatic if not severe cases of COVID-19.

A third explanation relates to the level of PCR testing carried out in the two countries. Israel uses a more sensitive or stringent PCR testing regime than the UK.

Genetic matter from the virus is amplified in cycles by PCR tests. The more cycles that are run, the more likely the lab is to detect the virus. Israel uses 37 amplifying cycles, which means that you are positive for the coronavirus even if the test process required up to 37 cycles to detect the virus.

“If the PCR testing is less sensitive, England may miss some cases – or Israel may catch more cases – and that could play a role in the numbers,” Cohen said. 

FINALLY, a separate study that was published over the weekend by the UK’s Department of Health and Social Care found that an eight-week gap between the first and second doses of the Pfizer vaccine is a “sweet spot” when it comes to generating neutralizing antibodies. 

When England launched its vaccination campaign, it did not have enough doses to vaccinate the population according to Pfizer’s recommended regime of two doses three weeks apart. As such, it spread doses out to between four and 12 weeks to allow more people to get at least one jab. 

Specifically, the new research showed that neutralizing antibody levels, the level of those antibodies responsible for defending cells from pathogens, were higher after the extended dosing interval (six to 14 weeks) compared to the conventional three-to-four-week regime.

In contrast, the T cell response was of a marginally lower magnitude after the longer dosing interval. T cells provide longer-term immunity and scientists believe that they could provide some immunity to COVID-19, even when antibodies become less effective at fighting the disease.

“The question is would you wait eight weeks when there is a pandemic?” Cohen asked, noting that separate studies have shown that one dose of the Pfizer vaccine is only around 30% effective against the Delta variant, which would leave the population vulnerable for two months. “It’s a tough question.”

Cohen's solution is to provide a third shot to the most vulnerable people, which new research is starting to show does a good job in boosting antibody levels.

“We are still learning the best way to immunize people with these vaccines,” he said. “But we are still in the middle of the pandemic.”

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