COVACPREG, a French prospective cohort study of women vaccinated against COVID-19 during pregnancy.

The objective of this cohort study was to describe the French population of pregnant women vaccinated against coronavirus disease 2019 (COVID-19), their pregnancy outcomes and the health status of their newborns (malformation rate, neonatal diseases, etc.), and to proactively collect and analyze reported adverse reactions over time. We conducted a prospective study using an online questionnaire. Women vaccinated during pregnancy who wanted to participate were asked to complete an inclusion questionnaire (dates of pregnancy and vaccination COVID-19, etc.), a questionnaire on the potential occurrence of adverse reactions (time of onset, type of adverse reaction, etc.) of the vaccination, sent 1 month after the injection, and a final questionnaire on the outcome of the pregnancy and the health status of the child. A total of 938 women were prospectively included in this first French study. A total of 132 women reported having had at least 1 adverse reaction following vaccination during pregnancy (14.1%), including few 'serious' adverse reaction (5.3%). There were no signals of adverse reactions during continuous monitoring. Among the 938 pregnant women, 22.4% received the vaccination COVID-19 during the first trimester, 64.2% during the second and 33.4% during the third trimester (some women have had several injections in different trimesters). Among the 938 women, 4.3% developed gestational hypertension and 13.9% diabetes; 3.3% had intrauterine growth restriction and 7.8% threatened preterm delivery. These rates are comparable to those observed in the French general population. Among live births, the rate of preterm birth was 5.1%. We reported a prevalence of major malformations of 3.9%, which is comparable to that reported by European Surveillance of Congenital Anomalies (EUROCAT), with a rate of 3.5% of major malformations in the general population of mainland France. In conclusion, our study did not demonstrate any particular safety signals in the event of vaccination with a Covid-19 vaccine during pregnancy.

Limited host availability disrupts the genetic correlation between virulence and transmission.

Virulence is expected to be linked to parasite fitness via transmission. However, it is not clear whether this relationship is genetically determined, nor if it differs when transmission occurs continuously during, or only at the end of, the infection period. Here, we used inbred lines of the macroparasitic spider mite Tetranychus urticae to disentangle genetic vs. nongenetic correlations among traits, while varying parasite density and opportunities for transmission. A positive genetic correlation between virulence and the number of transmitting stages produced was found under continuous transmission. However, if transmission occurred only at the end of the infection period, this genetic correlation disappeared. Instead, we observed a negative relationship between virulence and the number of transmitting stages, driven by density dependence. Thus, within-host density dependence caused by reduced opportunities for transmission may hamper selection for higher virulence, providing a novel explanation as to why limited host availability leads to lower virulence.