Have corona vaccines become less effective?

Experts said coronavirus vaccines remain “incredibly effective” despite fears that immunity may decline over time.

There have been some concerns about the effectiveness of COVID-19 vaccines after a number of recent studies pointed to a growing number of so-called “hacked” COVID cases among the fully vaccinated. However, studies have shown that fully vaccinated people are still highly protected against serious infections, hospitalization and death from viruses.

Preliminary data released by the Israeli government in July showed Pfizer vaccine efficacy dropped to just 16% against symptomatic infection for people who received two doses in January and for people who were fully vaccinated in April. , the vaccine was 79% effective against highly symptomatic infections, indicating that immunity acquired through immunization wears off over time.

Pfizer-funded research, published in July, showed the Pfizer-Biontech vaccine efficacy was strongest between a week and two months after receiving the second dose, reaching 96.2 percent. However, it decreased at a rate of 6% every two months. Four to six months after the second dose, its effectiveness was approximately 84%.

Meanwhile, one studio British published in August on over a million fully vaccinated people found that protection from Oxford-AstraZeneca and Pfizer vaccines waned over time. The analysis showed that one month after receiving a second dose of Pfizer vaccine, the protection against the virus was 88%. After five to six months, this protection was reduced to 74%.

While protection reached 77% per month after full vaccination with the AstraZeneca vaccine, it dropped to 67% after four to five months.


The launch of vaccination in Israel was one of the fastest in the world. But despite this, the number of COVID-19 cases in Israel has risen sharply since July.

In late July, Israel began offering a third dose of the vaccine to all people over the age of 60. Its recall program was quickly expanded, and the third shot has been available to anyone over 30 in the country since August.

A specialist in infectious diseases at Sheba Medical Center which has treated patients with COVID in Israel, the professor Eyal Leshem told CNBC that while cases increased despite a high vaccination rate, the rate of serious illness in the country remained “much lower”.

“We attribute this to the fact that most of our adult population is vaccinated with two doses and more than a million people have received the third booster dose,” he added.

He explained that rates of serious illness in vaccinated people are about one-tenth of those seen in unvaccinated people, which means that the vaccine is still more than 90% effective in preventing serious illness, and short-term data shows that ” people who have also received a booster dose are much less likely to be infected.

In turn, American infectious disease expert Richard Reithinger and vice president of global health at RTI International said that most vaccines developed for Covid-19 “are no less surprisingly effective, even with new emerging variables” .

“The conclusive proof of this is that cases, serious illnesses that require hospitalization in hospital and deaths decreased in significantly in countries that have rapidly expanded vaccination coverage, “he said.

delta effect

One studio published in May found that the Pfizer vaccine was 88% effective in preventing symptomatic disease of the delta variant and 93% effective against the alpha variant. AstraZeneca was also 60% effective in preventing symptoms of the delta variant, compared with a 66% efficacy rate against the alpha variant.

Are recall shots the answer?

Several countries, including the United States and the United Kingdom, are now providing – or planning to introduce – third doses of COVID-19 vaccines to help boost immunity against a virus that may have been depleted.

According to Gideon Schreiber, a professor at the Israel Weizmann Institute of Science, booster injections could become a necessity.

“Unfortunately, this will not happen every year, but twice a year,” he predicted. “The virus has huge potential for new variants, many of which will silence immunity, so there’s a chance we’ll need more boosters. in future”.

Schreiber added that the third dose has so far been shown to work with great success. After the second dose, people were four to five times less likely to develop serious Covid disease. But after a third dose, they are more than ten times less likely to seriously contract the virus.

However, Reithinger argued that recall shots weren’t necessarily a logical move in this moment.

“There is limited data available that the immune response modeled by the available vaccines decreases after six to eight months,” he told CNBC. via e-mail. Most of the data is about infection, not hospitalization or death. The data also does not take into account the use of non-pharmacological interventions, such as masking and social distancing, which should continue to be used and respected. in many contexts.

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