Interval of 6–7 weeks between vaccine doses may be better than a 3–4 weeks interval

Grunau et al. (2021). A higher antibody response is generated with a 6- to 7-week (vs standard) SARS-CoV-2 vaccine dosing interval. Clinical Infectious Diseases.

This study analyzed the immune response of paramedics who received the initial two mRNA COVID vaccines at different intervals. They found higher levels of COVID-19 antibodies in those who received the longer interval (42-49 days), compared to those who received the short interval (17-28 days). Spacing out the two vaccine doses by 6-7 weeks may offer improved immunity compared to 3-4 weeks.

Dosing interval of 5.5 weeks may be the shortest to achieve an enhanced immune response to vaccine

Asamoah-Boaheng et al. (2022). Determining the optimal SARS-CoV-2 mRNA vaccine dosing interval for maximum immunogenicity. Cureus.

Vaccinated participants provided a blood sample six months after the first dose. Compared to 30 days or less, waiting 39 days or more between doses increased antibodies against the original COVID-19 strain and Delta variants. Although waiting longer, from 74 to 123 days, enhanced the immune response further, 39 days is the shortest interval between doses that would achieve the highest long-term immune response.

Increased intervals between vaccines lead to increased antibody levels

Grunau et al. (2022). Immunogenicity of extended mRNA SARS-CoV-2 vaccine dosing intervals. Journal of the American Medical Association.

Researchers studied the antibody levels in paramedics who received mRNA vaccines at different intervals. Longer intervals between doses resulted in higher average antibody levels and increased ability to neutralize the virus. These results did not change based on when the blood test was conducted in relation to the first or second dose, confirming that delaying the second dose may offer faster partial protection to a large population when vaccine supplies are limited.

Long-term protection against COVID-19 is better with Moderna vaccines

Grunau et al. (2022). Comparative 6-month wild-type and delta-variant antibody levels and surrogate neutralization for adults vaccinated with BNT162b2 versus mRNA-1273. Microbiology Spectrum.

This study compared how effective the Pfizer and Moderna vaccines were in producing antibodies and preventing the virus from attaching to cells. Participants who were vaccinated with two doses of the Moderna vaccine had stronger protection six months after the first dose, against both the original strain and Delta variant of the virus, compared to those who received two doses of the Pfizer–BioNTech vaccine.

Pre-existing immunity to common cold may strengthen immune response to COVID-19 vaccines

Asamoah-Boaheng et al. (2022). Are higher antibody levels against seasonal human coronaviruses associated with a more robust humoral immune response after SARS-CoV-2 vaccination? Frontiers in Immunology.

In this study, people with higher levels of antibodies against certain common human coronaviruses, responsible for causing “the common cold," also exhibited a stronger immune response induced from COVID-19 vaccines. This suggests that having pre-existing immunity to common coronaviruses may enhance the effectiveness of COVID-19 vaccines in generating an immune response.

Measuring antibody levels is effective for measuring immune response to COVID-19 vaccines

Grunau et al. (2022). Correlation of SARS-CoV-2 viral neutralizing antibody titers with anti-spike antibodies and ACE-2 inhibition among vaccinated individuals. Microbiology Spectrum.

Live viral neutralizing antibody tests are expensive and time-consuming but are considered the gold standard for evaluating antibody effectiveness. In contrast, tests for COVID-19 antibodies and related enzyme activity are simpler and cheaper. Researchers compared these tests to live viral neutralizing antibody tests in vaccinated individuals and found a correlation, suggesting that these antibody tests can reliably assess post-vaccination immunity.


Evaluating the ability of a blood test to detect prior COVID-19 infections in a vaccinated population

Asamoah-Boaheng et al. (2022). Evaluation of the performance of a multiplexed serological assay in the detection of SARS-CoV-2 infections in a predominantly vaccinated population. Microbiology Spectrum.

This study investigated if blood antibody tests can detect a prior COVID-19 infection, and whether this was impacted by vaccination. Since many vaccines target the spike protein of the virus, spike antigen tests are unsuitable for detecting past infections. Instead, antibody measurements to detect a viral protein called nucleocapsid were used. Different criteria were needed for optimal test performance between vaccinated and unvaccinated groups, especially for recent COVID-19 infection. There were fewer false positives among unvaccinated compared to vaccinated individuals.

Existing tests to identify prior COVID-19 infection work in vaccinated and unvaccinated groups

Grunau et al. (2022). Sensitivity of the Elecsys nucleocapsid assay for the detection of preceding SARS-CoV-2 infections. Open Forum Infectious Diseases.

Tests for nucleocapsid antibodies are highly effective at detecting past COVID-19 infections in people who have not been vaccinated. This study found that a nucleocapsid test, different from the one assessed in the previous study, was just as good at detecting past infections in vaccinated individuals as it was in unvaccinated individuals.


Vaccinated paramedics are not at higher risk of COVID-19 infection than the general public

Grunau et al. (2022). A prospective observational cohort comparison of sars-cov-2 seroprevalence between paramedics and matched blood donors in Canada during the COVID-19 pandemic. Annals of Emergency Medicine.

Research on blood samples from paramedics and a control group of blood donors found the rates of prior COVID-19 infection were similar in both groups, suggesting that paramedics did not face a greater risk of infection. Among those who were not vaccinated, however, the proportion of paramedics with a previous COVID-19 infection was triple that of unvaccinated blood donors, suggesting that there is an occupational risk, but that the risk is mitigated with vaccination.

Higher antibody levels may reduce risk of breakthrough COVID-19 in vaccinated adults

Asamoah-Boaheng et al. (2022). The relationship between anti-spike SARS-CoV-2 antibody levels and risk of breakthrough COVID-19 among fully vaccinated adults. Journal of infectious Diseases.

This study examined the relationship between antibody levels in vaccinated paramedics without prior COVID-19 infection and their risk of future infection. Higher levels of antibodies against the original COVID-19 virus were linked to a significantly lower risk of subsequent infections. However, during the Omicron wave, the association between antibody levels and lower infection risk was weaker, likely due to the variant’s distinct characteristics.

Haig, Tom and Macdonald (2023). Data in the dark days: How paramedic-led research improved workplace safety. Canadian Paramedicine.