Vaccine and previous infection may provide enhanced protection against COVID-19

Two new studies in JAMA find that COVID-19 survivors who receive two doses of the Pfizer / BioNTech or Moderna mRNA vaccines may have stronger protection against coronavirus infection, one detailing much lower breakthrough infection rates among Qataris previously infected and the other describing higher peak antibody levels among recovered American healthcare workers (TS).

Revolutionary cases 65% to 82% lower in previously infected people

Led by researchers at Cornell University in Qatar, the first study consisted of following 1,531,736 Qataris from 14 days after receiving the second dose of Pfizer or Moderna COVID-19 vaccine from December 21, 2020 to September 19 2021.

The country resisted two outbreaks of COVID-19 with the Alpha (B117) and Beta (B1351) variants from January to June 2021. Community transmission of the SARS-CoV-2 Delta (B1617.2) variant was identified late March, and the strain became dominant in the summer.

The Pfizer group consisted of 99,226 COVID-19 survivors and 290,432 naive SARS-CoV-2 witnesses; the median age was 37 and 68% were males. The Moderna group consisted of 58,096 COVID-19 survivors and 169,514 never-infected witnesses; the median age was 36 and 73% were males.

Only 9% of Qatar’s residents are 50 or older, 89% are in the country with work visas from more than 150 counties, and most are men, the study’s authors said.

Within the Pfizer group, 159 (0.16%) COVID-19 infections were reported in COVID-19 survivors, of whom 1 was critically ill with the new infection, while 2,509 (0.86%) were are produced in those without previous infection. Of these, 26 had serious illness and 2 were in critical condition.

In the Moderna group, 43 breakthrough infections (0.07%) occurred in COVID-19 survivors, but none are serious, compared with 368 (0.22%) breakthrough infections in COVID-19 survivors. coronavirus naive participants, 1 of whom became seriously ill.

None of the Pfizer or Moderna vaccinees died.

The cumulative incidence of breakthrough infections in Pfizer vaccinees was estimated to be 0.15% (95% confidence interval [CI], 0.12% to 0.18%) in COVID-19 survivors and 0.83% (95% CI, 0.79% to 0.87%) in those without infection prior to 120 days of follow-up (adjusted risk ratio [aHR] for infection in naive coronavirus vaccinees, 0.18 [95% CI, 0.15 to 0.21]).

Among Moderna vaccinees, the cumulative incidence of infection was estimated to be 0.11% (95% CI, 0.08% to 0.15%) in those previously infected and 0.35% (95% CI, 0.32% to 0.40%) in those who had not been vaccinated at 120 days of follow-up. -up (aHR, 0.35 [95% CI, 0.25 to 0.48].

In other words, those who were infected with SARS-CoV-2 before being vaccinated had a breakthrough infection rate 65% to 82% lower than those who were vaccinated but never infected.

Timing of vaccination after infection seems important

COVID-19 survivors infected 6 months or more before their first vaccine dose had a significantly lower risk of reinfection than those infected less than 6 months before the first dose (aHR, 0.62 [95% CI, 0.42 to 0.92]) for Pfizer and 0.40 [95% CI, 0.18 to 0.91] for Moderna.

The study authors cautioned that, because the study was observational, they could not directly compare the risks of infection between the two vaccines, but that the combination of natural and vaccine-induced immunity appeared to be protective. .

“Although the 2 vaccines were shown earlier in Qatar to be very effective against the Alpha, Beta and Delta variants, a previous infection among those vaccinated – a hybrid of natural immunity and vaccine – appeared to be associated with a further reduction in the ‘revolutionary infection,’ he added. the researchers wrote.

COVID survivors have more antibodies

In the second study, researchers at Johns Hopkins University compared the durability of peak IgG antibodies to SARS-CoV-2 in fully vaccinated healthcare workers with and without previous COVID-19 infection from June 2020 to 3 September 2021. Participants provided serum samples 14 days after receiving the second dose of Pfizer or Moderna vaccine, and then again at least 90 days later.

Of the 1,960 healthcare workers who donated serum samples, 73 (3.7%) had evidence of a previous infection with SARS-CoV-2, of which 41 tested positive for COVID-19 in the 90 days before vaccination and 32 of them tested positive for more than 90 days. before vaccination. Of this group, 80% were female, 95% were non-Hispanic, and 80% were white; the median age was 40.4 years.

Among coronavirus-naive participants, the adjusted median antibody concentrations were 8.69 at 1 month, 7.28 at 3 months, and 4.55 at 6 months after vaccination (the possible range was 1.23 to 11 , 00).

Compared with never-infected participants, COVID-19 survivors maintained higher adjusted antibody levels after vaccination by an absolute difference of 1.25 (relative difference, 14%) at 1 month, 1.42 (19 %) at 3 months and 2.56 (56%) at 6 months.

Participants infected with COVID-19 more than 90 days before vaccination had higher adjusted antibody concentrations after vaccination than those infected within 90 days before vaccination, at 10.52 at 1 month (absolute difference, 0, 86; relative difference, 9%) and 9.31 at 3 months (absolute difference, 1.09; relative difference, 13%).

“Consistent with work comparing extended vaccine dosing intervals, the study showed that a longer interval between infection and the first vaccine dose may improve the antibody response,” the authors wrote.

In a Johns Hopkins press release, lead author Aaron Milstone, MD, MHS, said the findings helped elucidate the mechanisms of immunity against SARS-CoV-2.

“This finding adds to our understanding of how SARS-CoV-2 immunity works and builds on an earlier study by our team that showed mRNA vaccines produced a strong antibody response, even if a person did not develop significant symptoms after vaccination or had no previous infection with SARS-CoV-2, ”he said.

Researchers called for new studies to find out whether the increased durability of antibodies in COVID-19 survivors can be attributed to the number of exposures, the interval between exposures, or the interaction of natural and induced immunity. by the vaccine. “Studies are needed to elucidate how serological testing can inform the optimal timing of the vaccine and the need for booster doses,” they said.

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