Do people who’ve already had COVID-19 need BOTH doses of the vaccine?

Biology/Immunity Vaccines

A: Possibly not. One shot may work as an effective booster in those previously infected.

Given the large number of people who have been infected by SARS-COV-2 in many countries and the continued scarcity of vaccine doses, understanding the impact of the vaccines on the immunity of those previously infected is an important question.

Several new studies have found that one dose of vaccine for those previously infected not just boosts, but SUPER boosts antibodies and overall immune response to SARS-CoV-2.

Chalk this up to more impressive news about the effectiveness of these vaccines.

➡️ Why do previously infected people need vaccines at all? Aren’t they protected by natural immunity?

There are still many unknowns about natural immunity to SARS-CoV-2 including how long it lasts. We do know that natural immunity is highly variable among people-for many it is high and durable but some people produce low levels of antibodies that quickly fall below detectable levels. COVID-19 vaccines are producing stronger and more consistent antibody responses, which is why vaccination is still recommended for those with previous infection.

Previous infection may also protect less well against the new variants. One of the new studies found that blood from previous COVID-19 patients was less effective at neutralizing the new South African B.1.351 variant. After one dose of vaccination with Pfizer or Moderna shot however, those antibodies rose a THOUSAND-fold, and could neutralize the new variant…. as well as the original SARS-CoV-1 virus from 2003 (WOW!).

Another recent study found that antibody levels in those previously infected after one dose are as high or HIGHER than in people who were never infected after two doses. This study also found that “reactogenicity,” or side effects to the vaccine due to the body’s immune response were higher in those previously infected, consistent with a strong response.

➡️ Will the other vaccines produce the same turbo-boosting immune response?

While the current studies only looked at the mRNA vaccines, the other available vaccines target the same SARS-CoV-2 spike protein, just delivered in a different way. Given that the immune system is already primed to recognize the antigen from previous infection, it is likely all of the vaccines will provide this strong boost (but more data is likely forthcoming).

➡️ What does this mean practically?

If you have a confirmed previous COVID-19 infection, you should still get vaccinated when you have the opportunity, due to the known variability in antibody response. The vaccine will act as a huge booster and remind your immune system how to annihilate the SARS-CoV-2 virus if it sees it again (even as a different variant). The CDC currently states it’s OK to delay vaccination if you’ve had COVID-19 within the last 90 days, as immunity is unlikely to wane that quickly.

➡️ What about my 2nd dose?

This new research has yet to be incorporated into new vaccine guidelines in the US, but scientists conducting the research are in touch with the CDC in hopes of changing the recommendations. France’s highest health authority has already recommended that people who have had COVID-19 receive only one dose of the vaccine, and we should soon see if other countries follow suit. For now if you were previously infected and already had a first dose, we’d say watch for any recommendation changes but don’t be stressed about securing a second dose when they are still scarce.
One challenge to this policy is that many people do not know whether they had a previous infection, and screening people for antibodies prior to vaccination may not be practical on a mass scale. Nonetheless, given the millions of confirmed COVID-19 cases in many countries, using only one dose on these individuals would free up many doses during a time of serious vaccine supply constraints.

For now, the Nerdy Girls give another three cheers for science and the amazing ability of the vaccines to TURBOCHARGE immune response way beyond what is seen from natural infection. YAY SCIENCE!!

Those Nerdy Girls

Further reading:

“People Who Have Had Covid Should Get Single Vaccine Dose, Studies Suggest”

“France recommends 1-shot for people who had virus”

Recent scientific studies:

MedRxiv – Robust spike antibody responses and increased reactogenicity in seropositive individuals after a single dose of SARS-CoV-2 mRNA vaccine

MedRxiv – Antibodies elicited by SARS-CoV-2 infection and boosted by vaccination neutralize an emerging variant and SARS-CoV-1

Figure Legend (from 1st study above):

Immunogenicity and reactogenicity of SARS-CoV-2 RNA vaccines. A: Quantitative SARS-CoV-2 spike antibody titers (ELISA, expressed as area under the curve, AUC) for 109 individuals. “Pre” represents the antibody response prior to vaccination while “post 2nd dose” indicates the immune responses mounted after the second vaccine dose. Note that some of the individuals with pre-existing immunity had antibody titers below detection (AUC of 1) at the time point prior to vaccination.

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