Are Covid vaccines becoming less effective?

Vaccines against Covid-19 are still “incredibly effective” despite fears that immunity may wane over time, experts have said.

The effectiveness of Covid-19 vaccines has raised some concern after a number of recent studies indicated a growing number of so-called “breakthrough” Covid cases among fully vaccinated people. However, studies have shown that people who are fully vaccinated are still highly protected against serious infections, hospitalizations and death caused by the virus.

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

Pfizer-funded research published in July showed that the effectiveness of the Pfizer-BioNTech vaccine was highest between one week and two months after receiving the second dose, reaching 96.2%. However, it then fell by 6% on average every two months. Four to six months after a second dose, its effectiveness has dropped to about 84%.

In August, meanwhile, a UK study of more than one million fully vaccinated people found that protection against the Oxford-AstraZeneca and Pfizer-BioNTech vaccines wore off over time. A month after receiving a second dose of the Pfizer vaccine, protection against the virus was 88%, according to the analysis. After five to six months, this protection fell to 74%.

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

At the end of July, Israel began offering anyone over the age of 60 a third dose of the vaccine. Its booster program quickly expanded and third injections have been available to everyone over 30 in the country since August.

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

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

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

Richard Reithinger, infectious disease expert and vice president of global health at US-based RTI International, told CNBC in an email that most of the vaccines developed for Covid-19 were “nothing. less than surprisingly effective, even with newer variants emerging “.

“The compelling evidence of this is that cases, serious illnesses requiring hospitalization and deaths have declined dramatically in countries that have rapidly increased immunization coverage,” he said.

“In countries with very high immunization coverage, such as Iceland with over 90%, virtually no serious cases and no deaths are reported. Likewise, in countries with moderate to high immunization coverage, such as the United States and Canada, severe cases and deaths are almost exclusively among the unvaccinated. “

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

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

The data showed the importance of having two doses of these vaccines because the effectiveness of the two injections against symptomatic delta variant infection was only 33% three weeks after the first dose, according to the study.

Reithinger told CNBC that if the virus continues to mutate, that doesn’t necessarily mean it will become more resistant to existing vaccines, however.

“The delta variant has been shown to be more transmissible than the other variants, and the vaccine’s efficacy is slightly lower than that of the alpha and beta variants. The kappa variant, which appeared in India around the same time, however, is not as transmissible, “he added. he stressed.

Several other countries, including the United States and the United Kingdom, are now offering – or planning to offer – third doses of Covid-19 vaccines to help build immunity against the virus that may have depleted.

Booster shots may become a necessity, according to Gideon Schreiber, a professor at the Weizmann Institute of Science in Israel.

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

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

However, Reithinger argued that the booster shots weren’t necessarily a logical step at this point.

“There is only limited data available indicating that an immune response initiated by available vaccines wanes after six to eight months,” he told CNBC by email. “Most of the data focuses on infection, rather than hospitalization or death. The data also does not account for the use of non-pharmaceutical interventions, such as masking and social distancing, which, in many contexts, should continue to be used and respected. The only population groups for which the case of booster injections can be advanced are the immunocompromised. “

However, he said booster shots may eventually become necessary if data shows that the effectiveness of vaccines against serious illness and death declines over time.

Schreiber is currently overseeing research into a therapeutic drug that would act as a “super plug”, physically blocking itself in the cell receptors to which the virus attaches. By striving to block the “entry ports” of cells rather than attacking the virus itself, scientists hope to stay abreast of any future mutations.

“It should work against future variants, because it doesn’t really attack the virus – the virus can change, but as long as the virus binds to it, it will block it,” he told CNBC.

However, Schreiber said the drug would not be something that could be used on a large scale.

“It’s too expensive and it’s not necessary,” he said. “The way I see it is that it would be given to people who contracted Covid and were in a high-risk group. It also does not have a long-term effect like a vaccine. “

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

“The best hope for those at risk is vaccination, an effective vaccine we have now and which can be improved by boosters, mixtures or other methods,” he said.

“Despite very [intense] research, it is very difficult to find effective treatments – viruses are not bacteria. So while we have developed good antibiotics that have drastically changed the course of bacterial infection, we do not have such good antivirals for many viruses that infect humans. “

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

Reuters reported that AstraZeneca is 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 the year, the news agency said.

“What I really believe is that we really need a drug,” Schreiber told CNBC. “There is a lot of effort to develop drugs, there is no reason not to believe that it will not come in the near future. It will come and that, I think, will end the story.”

He added: “The virus continues to mutate – new variants will come, but the speed of technological advancement is truly amazing. So I say there is no reason to despair.”