Covid-19 antibody study shows downside of not receiving second vaccine shot

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  • A new study found that after three months following the second mRNA shot, antibody response decreased by 20%.
  • The study, however, showed that antibodies increased fivefold after the second dose of the vaccine.
  • Additionally, it was proved that natural antibodies post-infection are not as effective against breakthrough infections as vaccine antibodies.

A new study shows that three months after the second Pfizer or Moderna vaccination, antibody response decreased by 20% in adults with prior cases of Covid-19.

The study published in Scientific Reports investigated antibody responses following the second vaccine dose.

Testing the vaccine response 

The study enrolled 27 participants, 13 of whom had previously had Covid-19 and 14 who hadn't contracted the virus.

Participants provided online consent and completed a survey about their Covid-19 status and symptoms. They received finger-stick dried blood spot (DBS) tests from April 2020 through May 2021. 

The blood samples were collected 18 days after the first dose of either the Pfizer or Moderna vaccine and twice after the second dose – after 20 days and 56 days respectively.

The scientists then used the blood samples to track antibodies after each dose and also tested for the Alpha, Beta and Gamma variants.  

Antibody response

The study findings show prior Covid-19 infection does not provide an antibody response as robust as that of vaccination.

This means it's easier for breakthrough infections to happen if the body only relies on natural post-infection antibodies.

The study also found that the level of antibodies increased fivefold after the second vaccine dose compared to after the first dose.

"Our study shows that prior exposure to SARS-CoV-2 does not guarantee a high level of antibodies, nor does it guarantee a robust antibody response to the first vaccine dose.

"For people who had mild or asymptomatic infections, their antibody response to vaccination is essentially the same as it is for people who have not been previously exposed," says co-author Thomas McDade in a press statement.

The research additionally shows that neutralisation of all variants was significantly lower at three months after the second dose compared to immediately afterwards.

The scientists found that three months after the second dose, antibody responses had declined by about 20%.

They also found people who had Covid-19 with multiple symptoms had a higher level of response than those who tested positive but had mild symptoms or were asymptomatic.

"As far as protection goes after vaccination, the story is the same for all the variants, including Delta.

"The vaccine provides good protection, but not as good protection as the original version of the virus for which the vaccine was designed. Combine that with the fact that immunity wanes over time, you get increased vulnerability to breakthrough infection.

"So, it's two strikes right now – Delta plus waning immunity among the first wave of the vaccinated," said McDade.

*For more Covid-19 research, science and news, click here. You can also sign up for our Daily Dose newsletter here.

READ | C.1.2 Covid-19 variant: Scientists 'fairly confident' vaccines will continue to provide protection

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