The new report says the effectiveness of the third dose wanes after four months, with natural immune antibodies lasting longer

After about four months, a third dose of the coronavirus vaccine is much less likely to prevent serious illness, according to a new study released Friday by the CENTERS for Disease Control and Prevention.

The study looked at cases in 10 states from August 26, 2021, to January 22, 2022. CDC data showed that during the Omicron era, the effectiveness of the third booster for hospitalizations dropped from 91 percent in the first two months after the injection to 78 percent in about the fourth month. At the same time, the effectiveness of the emergency department went from 87 percent at two months to 66 percent at four months, and only 37 percent after about five months.

The new data support previous studies that showed that the Pfizer and Modena vaccines, with either two or three doses, were less effective when Omicron and Delta were dominant.

The new study has limitations, though — the data did not differentiate between why people who received the third booster shot were vaccinated, did not break down effectiveness by age group, or say whether the people being followed had underlying health conditions. The cases followed did not take into account no medically reported viral infections and did not identify which variants were present in the cases.

The debate over whether vaccines should be used has raged throughout the COVID-19 pandemic, and while the CDC reports that vaccines are starting to wane again, a new Israeli study reignites the debate over whether natural immunity or vaccine-induced protection is better.

Israel was one of the first countries in the world to launch a vaccine. A recent report from the Sheba Medical Center in Ramat Gan, The country, shows that COVID-19 survivors who have never been vaccinated have more lasting immunity than those who have been vaccinated twice but have never been infected.

The study followed more than 500 people who had been infected or vaccinated twice between 2020 and 2021. Of those, 130 were people who became infected without vaccination between March 2020 and November 2021. 402 people who received the second injection at the end of 2020 but never became infected.

Participants were observed for up to a year, with experts measuring antibody levels in patients’ blood immediately after they were infected or vaccinated, and follow-up tests six months later. The researchers also measured antibody affinity – how well the infection-fighting protein binds to the target virus.

While the vaccinated people initially had higher levels of antibodies, they dropped by much more than the naturally immunized group. The vaccinated people initially saw higher levels of antibodies and higher affinity. But after six months, both measures were lower than those in the naturally immunized group, while antibody levels dropped more and more slowly in those who recovered. After six months, affinity actually seemed to increase. Although researchers can’t explain why.

The graph shows two distinct downward trends in antibody affinity — the degree to which the infection-fighting protein binds to the target virus — among COVID-19 survivors (red) or vaccinators (blue).

“While antibody quantity decreases over time in all cases, the quality of antibody increases after infection in unvaccinated COVID-19 survivors but not in vaccinated COVID-19 survivors,” the researchers wrote in the study.

But the Israeli-led study only looked at antibodies. Immunity also involves T cells and other white blood cells that are harder to measure but can provide longer-lasting protection. At the same time, the study does not necessarily reflect immunity to later variants such as Omicron.

The findings will be presented at the European Congress of Clinical Microbiology and Infectious Diseases in Lisbon, Portugal, in April.

In addition, in January, the CDC reported that people who had previously been infected with COVID-19 were more resistant to the Delta variant than those who had only been vaccinated, according to data from health departments in California and New York, suggesting that natural immunity was more effective than the vaccine against the variant.

Health officials in California and New York collected data from May to November 2021, including a period when the Delta variant was dominant. The study showed that protection against Delta was highest among vaccinated convalesces, followed by unvaccinated convalesces, and lowest among never-infected or vaccinated convalesces.

People who were vaccinated but not infected in California and New York had a 6.2-fold and 4.5-fold reduction in COVID-19 rates, respectively, compared with the base population that was neither infected nor vaccinated. But among unvaccinated survivors, the rate was 29 times lower in California and 14.7 times lower in New York. Those who were best protected from infection were vaccinated survivors, whose infection rates were 32.5 times lower in California and 19.8 times lower in New York.

A Danish study published in December also confirmed that natural immunity protects against infection better than vaccines. It shows that vaccine-induced immunity begins to weaken rapidly a few weeks after vaccination. At the five-month mark, the protection rate was well below 50%. Natural immunity, by contrast, is strong: protection remains above 70 per cent for a full year after infection.

“After two years of accumulating data, it is clear that natural immunity is superior to vaccination,” said Dr. Marty Makary of Johns Hopkins University. Makary notes that the United States is one of the few countries that ignores natural immunity.

But many experts say the “jury is still out” on whether natural immunity provides better protection against the virus.

Professor Danny Altman, an immunologist at Imperial College London, said: “This study touches on some of the difficult questions we are all grappling with in human immunology at this stage of the pandemic, and there is more work to be done. There is consensus on the quality, quantity, and durability of protective immunity through infection, vaccination, and the jury is still out.”

Dr Julian Tang, a clinical virologist at the University of Leicester, said: “In general, natural infections produce a broader and longer-lasting immune response to all viral antigens – so this is not surprising. After all, our immune system has evolved over millions of years to deal with all types of pathogens — so I expect natural immunity to trump any vaccine-induced immunity in the long run.”

But one consensus is that all scientists agree that a combination of vaccines and natural immunity is best. The risk of severe illness, hospitalisation, long-term sequelae and death from initial infection among unvaccinated persons remains substantial. The CDC also advises all eligible people to “stay up-to-date on recommended COVID-19 vaccinations to best protect against covid-cov-related hospitalizations and emergency care.”