Study shows 80% COVID-19 antibodies lost six months after second Pfizer vaccine dose; what this means

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COVID-19 antibodies produced by the Pfizer vaccine decreased more than 80 percent in senior nursing home residents and their caregivers six months after receiving their second dose, a US study has found.

The research led by Case Western Reserve University and Brown University in the US studied blood samples of 120 nursing home residents and 92 health care workers.

The researchers particularly looked at humoral immunity, also called antibody-mediated immunity, to measure the body's defences against the SARS-CoV-2 virus, which causes COVID-19.

What does the study say?

The yet-to-be-published study, posted on the preprint server medRxiv, found that individuals' antibody levels decreased more than 80 percent after six months. The results were the same in seniors, with a median age of 76, and caregivers, with a median age of 48, and old alike, according to the researchers.

Earlier research by the team found that within two weeks of receiving the second dose of vaccine, seniors who had not previously contracted COVID-19 already showed a reduced response in antibodies that was substantially lower than the younger caregivers' experience.

By six months after vaccination, the blood of 70 percent of these nursing home residents had "very poor ability to neutralise the coronavirus infection in laboratory experiments," said David Canaday, a professor at the Case Western Reserve University.

Early in the pandemic, higher COVID-19 mortality among nursing home residents in the US-led to making them a priority for vaccination, the researchers said.

Most nursing home residents received the Pfizer vaccine under the emergency use authorisations because it was the first available vaccine on the market, they said.

"With nursing home residents' poor initial vaccine response, the rise of breakthrough infections and outbreaks, characterisation of the durability of immunity to inform public health policy on the need for boosting is needed," the authors of the study added.

Are there any other studies to support this?

The results support the Centers for Disease Control and Prevention's (CDC), recommendation for booster shots especially for the elderly due to fading immunity. The study noted that the boosters are even more important as the Delta variant spreads.

CDC released a number of studies conducted during the delta surge that suggest that the vaccines remain highly effective at keeping Americans out of the hospital but that their ability to prevent infection is dropping markedly.

A separate study looked at reported COVID-19 infections in residents of nearly 15,000 nursing homes and other long-term care facilities. It found that the effectiveness of the Pfizer and Moderna vaccines against infection fell from about 74 percent in March, April and early May to 53 percent in June and July.

Another study was a look at 21 hospitals. It found that the vaccine's effectiveness in preventing COVID-19-associated hospitalizations was 86 percent at two to 12 weeks after the second dose, and 84 percent at 13 to 24 weeks after. The difference was not considered significant.

Also, the CDC released Mayo Clinic patient data from Minnesota that showed that in July, when the delta variant was prevalent, Moderna's vaccine was 76 percent effective against infection and Pfizer's 42 percent.

US health officials were already talking about the waning immune response at least since a month ago.

Health officials told The Associated Press in August that it is "very clear" that the vaccines' protection against infections wanes over time, and they noted the worsening picture in Israel, which has seen a rise in severe cases despite an impressive vaccine coverage, should ring alarm bells.

As for why the vaccines appear to be less effective over time at stopping infections, there are indications that the body's immune response to the shots fades, as it does with other inoculations. But also, the vaccines simply may not protect against the delta variant as well as they do against the original virus. Scientists are still trying to answer the question.

Officials said the eight-month timeframe was a judgment call about when vaccine protection against severe illness might fall, based on the direction of the current data. "There's nothing magical about this number," the surgeon general said.

In fact, Pfizer CEO Albert Bourla himself said that people will "likely" need a booster dose of a Covid-19 vaccine within 12 months of getting fully vaccinated. Bourla said its possible people will need to get vaccinated against the coronavirus annually.

Pfizer has already submitted an application to the US Food and Drug Administer for authorization of a third dose and the US government said last month that boosters would likely be available in late September. Israel has already started administering booster doses and similar plans are under consideration in other countries for vulnerable populations, including Britain, France and Germany.

Who's the most vulnerable?

Almost all studies unanimously point that the elderly and those with lower immunity are at the highest risk and hence the most in need for a booster shot.

About three percent of US adults are immunocompromised, according to the CDC, but research suggests they account for about 44 percent of hospitalised breakthrough cases of COVID-19. Not only are they more likely to get very ill from COVID-19, they also have a lower antibody response to vaccines and are at a higher risk of transmitting the virus.

What about the vaccine candidates available in India?

Unfortunately, a similar study analysing long-term immunity in the Indian population is yet to come out. The only efficacy data that we have on Indian vaccine candidates are based on the initial clinical trials and what the vaccine manufacturers claim.

However, a recent study by genome sequencing government consortium INSACOG on the number of breakthrough infections can shed some light on the long-term immunity response. The study, that was conducted on a small sample group of healthcare workers in Delhi found that 25.3 percent of previously uninfected, Covishield double vaccinated, healthcare workers were infected within a period of fewer than two months.

However, the study warned that this should not encourage people to skip vaccination because scientists still believe that inoculation protects people against severe disease.

COVID-19 infection gives strongest form of immunity

Researchers at Maccabi Healthcare Services in Tel Aviv released a preprint (a study that is yet to be reviewed by other experts) suggesting people who had been infected with COVID had greater protection than vaccinated people against becoming reinfected with the delta variant.

Infection exposes our immune system to several viral proteins, whereas the most commonly used COVID vaccines introduce a single antigen: the spike protein. This results in a more directed but also a more restricted immune response than after infection.

Although people who have had COVID can get reinfected, naturally acquired immunity continues to evolve over time and antibodies remain detectable for longer than was first anticipated. New evidence suggests that immunity following both severe and mild infection protects against both symptomatic and asymptomatic reinfection.

But this does not discount the risks associated with contracting the infection the first time, given that disease progression is unpredictable and much faster with new virulent strains.

Indeed, apart from the overt risks of severe illness or death, several recent studies show that otherwise healthy people who have recovered from COVID have a substantially increased risk of longer-term serious health problems, including myocarditis (inflammation of the heart muscle), blood clots and stroke, compared to vaccinated people. And the most rigorous safety monitoring in US history has shown that COVID vaccines are safe and effective.

With cases surging globally and deaths driven by the delta variant, waiting for infection €" and risking long-term health problems, severe illness and death €" to achieve immunity to the very same infection is as fruitless as it is dangerous.

With inputs from agencies

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