Pandemic influenza viruses often cause severe disease in middle-aged adults without preexistent co-morbidities. The mechanism of illness associated with severe disease in this age group is not well understood1–10. Here, we demonstrate preexisting serum antibody that cross-reacts with, but does not protect against 2009 H1N1 influenza virus in middle-aged adults. Non-protective antibody is associated with immune complex(IC)-mediated disease after infection. High titers of serum antibody of low avidity for H1-2009 antigen, and low avidity pulmonary ICs against the same protein were detected in severely ill patients. Moreover, C4d deposition - a sensitive marker of complement activation mediated by ICs- was present in lung sections of fatal cases. Archived lung sections from adults with confirmed fatal influenza 1957 H2N2 infection revealed a similar mechanism of illness. These observations provide a novel biological mechanism for the unusual age distribution of severe cases during influenza pandemics.

The study aimed to determine the incubation period of Babesia sp. infection in naive cattle and to monitor the serological response once exposed to natural Boophilus microplus (Rhipicephalus microplus)-infested paddocks. The study was carried out on a farm located in Veracruz, Mexico. Five groups of five steers were relocated every 3 months from a tick-free area to a tick-infested paddock. Animals were introduced in October, January, April, July, and October. Blood samples were taken daily until day 21 to determine packed cell volume (PCV), percentage of parasitized erythrocytes (PPE), and antibody titers to Babesia bigemina and B. bovis by the indirect fluorescent antibody procedure. Detection of Babesia in blood was also performed by species-specific PCR. The estimated incubation period was 6-14 days post introduction to paddocks (PIP), with fever (41 degrees C) for at least 3 days. PCV decreased by >25% and Babesia parasites were observed during the clinical phase of the disease. The highest individual PPEs (0.44% and 0.22% for B. bovis and B. bigemina, respectively) were observed from animals introduced in October. The four other groups showed a mean PPE ranging from 0.002-0.146% at day 14 PIP. All animals were detected as PCR positive between 8-14 days PIP. The highest antibody titers were 1:3328. The environmental conditions were favorable throughout the year for tick reproduction as the farm showed enzootic stability and hyperendemic conditions for bovine babesiosis. In this type of farm, strategic tick control could be accompanied by babesiosis vaccination, particularly for cattle relocated from tick-free areas.

Liver transplantation (LT) recipients (LTRs) were not included in severe acute respiratory disease coronavirus 2 (SARS-CoV-2) vaccine registration trials, and therefore the clinical efficacy of the different vaccines for this group of patients who are immunosuppressed is not yet known. Recent work has demonstrated a reduced humoral immune response after administration of SARS-CoV-2 messenger RNA (mRNA)-based vaccines to solid organ transplantation recipients (SOTRs), (1)(2)(3) especially in kidney transplantation recipients. However, there is still not enough information regarding the use of different vaccine platforms in LTRs. Recently, Rabinowich et al. (4) reported that only 47.5% of LTRs vaccinated with BNT162b2 (Pfizer-BioNTech, New York, NY, USA) developed specific anti-SARS-CoV-2 antibodies 2 or 3 weeks after the second dose administration. However, Strauss et al. (5) reported that LTRs vaccinated with 2 doses of SARS-CoV-2 mRNA-based vaccines developed a much more robust humoral response compared with other SOTRs. Development of a robust humoral response against different vaccine platforms in LTRs remains an open question. In this work, we compared anti-SARS-CoV-2 antibody response in a study group of LTRs and a healthy control group after the 2-dose series of either inactivated virus CoronaVac (Sinovac Life Sciences Co., Beijing, China) or BNT162b2 vaccines. prieto et al.