Are Covid vaccines becoming less effective?

Covid-19 vaccines are still “stunningly effective” despite fears that immunity may dwindle over time, experts have said.

There have been some concerns about the efficacy of Covid-19 vaccines after a number of recent studies indicated a growing number of so-called “breakthrough” Covid cases among the fully vaccinated. The studies have, however, shown that the fully vaccinated are still highly protected against severe infection, hospitalization and death caused by the virus.

Preliminary data published by the Israeli government in July showed that the Pfizer vaccine was just 16% effective against symptomatic infection for people who had received two doses in January. For people who had been fully vaccinated by April, the vaccine was 79% effective against symptomatic infection, suggesting that immunity gained through immunization depletes over time.

A piece of research funded by Pfizer, published in July, showed that the efficacy of the Pfizer-BioNTech vaccine was strongest between one week and two months after receiving the second dose, coming in at 96.2%. It then, however, declined by an average of 6% every two months. Four to six months after a second dose, its effectiveness fell to around 84%.

In August, meanwhile, a U.K. study of more than one million fully vaccinated people found that protection from both the Oxford-AstraZeneca and the Pfizer-BioNTech vaccines faded over time. A month after receiving a second dose of the Pfizer vaccine, protection against the virus stood at 88%, the analysis showed. After five to six months, that protection fell to 74%.

Protection stood at 77% a month after being fully vaccinated with the Oxford-AstraZeneca vaccine, and fell to 67% after four to five months.

Israel’s vaccination rollout was one of the fastest in the world. But despite this, the number of Covid-19 cases in Israel have been rising sharply since July. 

In late July, Israel began offering everyone over the age of 60 a third vaccine dose. Its booster program has been rapidly expanded and third shots have been available to everyone over the age of 30 in the country since August.

Professor Eyal Leshem, an infectious disease specialist at Sheba Medical Center who has been treating Covid patients in Israel, told CNBC that while cases were rising despite a high vaccination rate, the rate of severe illness in the country remained “substantially lower.”

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

“The severe disease rates in the vaccinated are about one-tenth of those seen in the unvaccinated, which means the vaccine is still over 90% effective in preventing severe disease,” Leshem added. “People who received the booster dose are also at much, much lower risk of becoming infected, our short-term data shows.”

Richard Reithinger, an infectious disease expert and vice president of global health at U.S. based RTI International, told CNBC in an email that most of the developed vaccines for Covid-19 were “nothing short of stunningly effective, even with the newly emerging variants.”

“Irrefutable proof for that is how cases, severe disease requiring hospitalization and deaths dramatically dropped in countries that rapidly scaled-up vaccination coverage,” he said.

“In countries with very high vaccine coverage, such as Iceland with more than 90%, hardly any severe cases and deaths are being reported. Similarly, in countries with moderate to high vaccine coverage, like the U.S. and Canada, severe cases and deaths are almost exclusively seen in the unvaccinated.”

An earlier English study, published in May, found that the Pfizer-BioNTech vaccine was 88% effective at preventing symptomatic disease from the delta variant. Against the alpha variant, once the dominant strain in the U.K., the vaccine was 93% effective at preventing symptomatic disease.

Meanwhile, the research found that two doses of the Oxford-AstraZeneca vaccine were 60% effective at preventing symptomatic disease from the delta variant, compared to a 66% efficacy rate against the alpha variant.

The data showed the importance of having two doses of these vaccines as the efficacy of both shots against symptomatic infection from the delta variant stood at just 33% three weeks after the first dose, the study found.

Reithinger told CNBC that if the virus continued to mutate, it did not necessarily mean it would become more resistant to existing vaccines however.

“The delta variant has been shown to be more transmissible than other variants, and vaccine effectiveness is slightly lower than for the alpha and beta variants. The kappa variant, which emerged in India around the same time, however, is not as transmissible,” he highlighted.

Several more countries, including the U.S. and the U.K., are now offering — or planning to offer — third doses of Covid-19 vaccines to help boost immunity to the virus that may have depleted.

According to Gideon Schreiber, a professor at Israel’s Weizmann Institute of Science, booster shots may become a necessity.

“Unfortunately, it’s not even [going to be] annually, it will be twice annually,” he predicted. “The virus has a huge potential for new variants, many which will work to silence immunity — so there’s a chance that we’ll need further boosters in the future.”

Schreiber added that Israel’s booster program appeared, so far, to be a big success. After a second dose, he told CNBC, people were four or five times less likely to become severely ill with Covid. But after a third dose, they were more than ten times less likely to become severely ill with the virus.

However, Reithinger argued that booster shots were not necessarily a logical step at this point in time.

“There is only limited data available that an immune response that was primed by available vaccines is waning after six to eight months,” he told CNBC via email. “Most of the data is on infection, rather than hospitalization or death. The data also doesn’t account for the use of non-pharmaceutical interventions, such as masking and social distancing, that in many contexts should continue to be used and adhered to. The only population groups for which the case for booster shots can be made is the immunocompromised.”

However, he said that booster shots may eventually become necessary if data prove the vaccines’ efficacy against severe disease and death wanes over time.

Schreiber is currently supervising research on a therapeutic drug that would act as a “super-cork,” physically jamming itself into cell receptors that the virus attaches itself to. By working to block cells’ “entry ports” rather than attacking the virus itself, scientists are hoping to stay on top of any future mutations.

“It should work against future variants, because it’s not really going after the virus — the virus can change, but as long as the virus binds to it, it’s going to block it,” he told CNBC.

However, Schreiber said the drug wouldn’t be something that could be used on a wide scale.

“It’s too expensive, and there’s no need,” he said. “The way I see it is that it would be given to people who got Covid and were in a high-risk group. It also doesn’t have a long-term effect like a vaccine.”

The Sheba Medical Center’s Leshem argued that vaccinations were currently the best hope society had of finding a state of “equilibrium” with the virus, where the virus could circulate without severe repercussions.

“The best hope for people at risk is immunization, an effective vaccine, which we currently have, and may be improved through boosters, through mixing or through other methods,” he said.

“Despite very [intense] research, it’s very challenging to find effective treatments — viruses are not bacteria. So while we’ve developed good antibiotics that have dramatically changed the course of bacterial infection, we do not have such good antivirals for many of the viruses that infect humans.”

Pharmaceutical companies are also looking at new treatments to prevent Covid aside from vaccines.  In mid-August, AstraZeneca published results from a phase three trial of an antibody therapy which was found to reduce the risk of developing symptomatic Covid-19 by 77%. There were no deaths or cases of severe illness among the 25 participants who contracted symptomatic Covid during the trial.  A total of 5,172 people took part in the trial, 75% of whom had co-morbidities.

Reuters reported that AstraZeneca was seeking conditional approval for the therapy in major markets this year. The pharmaceutical giant would produce 1 to 2 million doses by the end of this year, the news agency said.

“What I really believe is that we really need a medicine,” Schreiber told CNBC. “There are many efforts in developing drugs, there is no reason not to believe it will not come in the near future. It will come and this basically, I think, will end the story.”

He added:”The virus keeps mutating — new variants will come, but the speed of technological advances is really amazing. So I say there’s no reason to despair.”